general adult inclusion criteria: 1. willing and able to sign informed consent 2. documented full covid-19 vaccination (cdc card or documentation in medical records) that was completed at least 4 weeks prior and no more than 52 weeks prior to the stage 1 screening visit, or if participating in stage 2, no more than 48 weeks prior to the stage 2 screening visit. general exclusion criteria 2. history of severe allergic reaction to the initial covid-19 vaccine regimen, to any component of any of the covid-19 vaccines, or to polyethylene glycol (peg). 3. new diagnosis of malignancy that will require chemotherapy or immunotherapy, or ongoing treatment for a malignancy with chemotherapy or immunotherapy. 4. active disease (per the investigator's decision) resulting in inability to hold the is therapy in the mmf/mpa or mtx arms of the study. a. the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered. 5. active disease during the screening period resulting in: 1. an increase/addition of any is medications, or 2. a suggestion of ms relapse per the investigator. 6. recent or current sars-cov-2 infection defined as: <!-- --> 1. documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening). 2. positive result on a molecular covid-19 test at screening. 8. inflammatory myocarditis/pericarditis within 6 weeks of any covid-19 vaccine doses. 9. participants with active, ongoing chronic infections. note: participants are permitted to be on chronic prophylactic antimicrobial therapy. adults with evidence of hiv, hepatitis b indicated by surface antigen, and hepatitis c indicated by anti-hepatitis c antibody positivity will be excluded. if an adult is negative for hepatitis c viral load at screening, he/she will be eligible to participate. 10. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy. note: pediatric participants on ivig therapeutically may enter the study provided they have sufficiently quiet disease that they can withhold their ivig from 8 weeks prior to the screening visit through 4 weeks after vaccination. 11. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening. 12. participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study. 13. currently pregnant or breastfeeding (for pediatric participants postmenarchal females must have a negative urine pregnancy test at screening). 15. hemoglobin (hgb) \<8.0 g/dl (80 g/l) 16. past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study. 17. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of screening. 18. concurrent treatment with cyclophosphamide. adult participants taking cladribine, alemtuzumab, or mitoxantrone will also be excluded. 19. participants currently on any type of dialysis, or who have received a solid organ transplant. 20. prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness. 21. taking both mmf/mpa and mtx. 22. receiving other investigational bcdt as part of a clinical trial within 18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. 23. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening. adult general criteria inclusion criteria: 1. individuals 18 years of age or older that meet classification criteria for systemic lupus erythematosus (sle), systemic sclerosis (ssc), rheumatoid arthritis (ra), multiple sclerosis (ms), or pemphigus 2. participants must meet the 2019 acr/eular or 2012 slicc classification criteria for sle, the 2010 acr/eular classification criteria for ra, the 2013 eular/acr classification criteria for ssc, the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus. <!-- --> 1. if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry 6. must be currently taking one of the following is medications with or without additional disease-related medications: mmf (minimum of 1000 mg per day)/mpa (minimum of 720 mg per day), mtx (minimum of 7.5mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, ofatumumab). <!-- --> 1. if taking mmf/mpa or mtx, the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen. note: participants who withheld their is medications around their initial vaccinations are eligible to participate. 2. if enrolling in the bcdt cohort, the participant must have received an anti-cd20 or an anti-cd19 bcdt in the past 18 months. 7. no changes in background is medications, including mmf/mpa or mtx, in the 4 weeks prior to screening, excluding the following: <!-- --> 1. hcq, 2. intraarticular steroids, 3. the addition of prednisone at ≤10mg per day or prednisone at any dose when given for ≤3 days, and 4. corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted. adult general exclusion criterion 1. inability or unwillingness of a participant to give written informed consent or comply with study protocol. 14. adult female participants who are planning a pregnancy during the course of the trial. adult stage 1-specific inclusion criterion 5. negative or suboptimal serologic response to initial covid-19 vaccine regimen, defined as an elecsys® anti-sars-cov-2 s result ≤200 u/ml, at screening visit. <!-- --> 1. initial covid-19 vaccine regimen is defined as either: i.2 doses of the pfizer-biontech covid-19 vaccine ii. 2 doses of the moderna covid-19 vaccine adult stage 1-specific exclusion criterion 7. receipt of a covid-19 vaccine booster prior to screening with the moderna covid-19 vaccine, pfizer-biontech covid-19 vaccine, or janssen covid-19 vaccine. adult stage 2 (newly recruited)-specific inclusion criteria 2. history of severe allergic reaction to the covid-19 vaccine, or to any component of the covid-19 vaccine, that is to be administered in stage 2, including polysorbate for participants receiving the sanofi-gsk covid-19 vaccine, or to peg. 5. negative or suboptimal serologic response to a previous covid 19 vaccine administration in one of the qualifying regimens, defined as an elecsys® anti-sars-cov-2 s (rbd) negative result or positive result of ≤200 u/ml, or a low immune response, defined as an elecsys® anti-sars-cov-2 s (rbd) result of ≤2500 u/ml, within 4 weeks of the stage 2 baseline/week 0 visit. the regimens of covid-19 vaccination that qualify are as follows: 1. 3 doses of the pfizer-biontech covid-19 vaccine 2. 3 doses of the moderna covid-19 vaccine 3. 2 doses of the janssen covid-19 vaccine 4. 4 or more doses of a single mrna vaccine (pfizer-biontech covid-19 vaccine or moderna covid-19 vaccine) 5. 3 or more doses of a mixture of mrna vaccines (pfizer-biontech covid-19 vaccine or moderna covid-19 vaccine) adult stage 2 (newly recruited)-specific

general adult inclusion criteria: 1. willing and able to sign informed consent 2. documented full covid-19 vaccination (cdc card or documentation in medical records) that was completed at least 4 weeks prior and no more than 52 weeks prior to the stage 1 screening visit, or if participating in stage 2, no more than 48 weeks prior to the stage 2 screening visit. general exclusion criteria 2. history of severe allergic reaction to the initial covid-19 vaccine regimen, to any component of any of the covid-19 vaccines, or to polyethylene glycol (peg). 3. new diagnosis of malignancy that will require chemotherapy or immunotherapy, or ongoing treatment for a malignancy with chemotherapy or immunotherapy. 4. active disease (per the investigator's decision) resulting in inability to hold the is therapy in the mmf/mpa or mtx arms of the study. a. the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered. 5. active disease during the screening period resulting in: 1. an increase/addition of any is medications, or 2. a suggestion of ms relapse per the investigator. 6. recent or current sars-cov-2 infection defined as: <!-- --> 1. documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening). 2. positive result on a molecular covid-19 test at screening. 8. inflammatory myocarditis/pericarditis within 6 weeks of any covid-19 vaccine doses. 9. participants with active, ongoing chronic infections. note: participants are permitted to be on chronic prophylactic antimicrobial therapy. adults with evidence of hiv, hepatitis b indicated by surface antigen, and hepatitis c indicated by anti-hepatitis c antibody positivity will be excluded. if an adult is negative for hepatitis c viral load at screening, he/she will be eligible to participate. 10. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy. note: pediatric participants on ivig therapeutically may enter the study provided they have sufficiently quiet disease that they can withhold their ivig from 8 weeks prior to the screening visit through 4 weeks after vaccination. 11. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening. 12. participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study. 13. currently pregnant or breastfeeding (for pediatric participants postmenarchal females must have a negative urine pregnancy test at screening). 15. hemoglobin (hgb) \<8.0 g/dl (80 g/l) 16. past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study. 17. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of screening. 18. concurrent treatment with cyclophosphamide. adult participants taking cladribine, alemtuzumab, or mitoxantrone will also be excluded. 19. participants currently on any type of dialysis, or who have received a solid organ transplant. 20. prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness. 21. taking both mmf/mpa and mtx. 22. receiving other investigational bcdt as part of a clinical trial within 18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. 23. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening. adult general criteria inclusion criteria: 1. individuals 18 years of age or older that meet classification criteria for systemic lupus erythematosus (sle), systemic sclerosis (ssc), rheumatoid arthritis (ra), multiple sclerosis (ms), or pemphigus 2. participants must meet the 2019 acr/eular or 2012 slicc classification criteria for sle, the 2010 acr/eular classification criteria for ra, the 2013 eular/acr classification criteria for ssc, the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus. <!-- --> 1. if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry 6. must be currently taking one of the following is medications with or without additional disease-related medications: mmf (minimum of 1000 mg per day)/mpa (minimum of 720 mg per day), mtx (minimum of 7.5mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, ofatumumab). <!-- --> 1. if taking mmf/mpa or mtx, the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen. note: participants who withheld their is medications around their initial vaccinations are eligible to participate. 2. if enrolling in the bcdt cohort, the participant must have received an anti-cd20 or an anti-cd19 bcdt in the past 18 months. 7. no changes in background is medications, including mmf/mpa or mtx, in the 4 weeks prior to screening, excluding the following: <!-- --> 1. hcq, 2. intraarticular steroids, 3. the addition of prednisone at ≤10mg per day or prednisone at any dose when given for ≤3 days, and 4. corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted. adult general exclusion criterion 1. inability or unwillingness of a participant to give written informed consent or comply with study protocol. 14. adult female participants who are planning a pregnancy during the course of the trial. adult stage 1-specific inclusion criterion 5. negative or suboptimal serologic response to initial covid-19 vaccine regimen, defined as an elecsys® anti-sars-cov-2 s result ≤200 u/ml, at screening visit. <!-- --> 1. initial covid-19 vaccine regimen is defined as either: i.2 doses of the pfizer-biontech covid-19 vaccine ii. 2 doses of the moderna covid-19 vaccine adult stage 1-specific exclusion criterion 7. receipt of a covid-19 vaccine booster prior to screening with the moderna covid-19 vaccine, pfizer-biontech covid-19 vaccine, or janssen covid-19 vaccine. adult stage 2 (newly recruited)-specific inclusion criteria 2. history of severe allergic reaction to the covid-19 vaccine, or to any component of the covid-19 vaccine, that is to be administered in stage 2, including polysorbate for participants receiving the sanofi-gsk covid-19 vaccine, or to peg. 5. negative or suboptimal serologic response to a previous covid 19 vaccine administration in one of the qualifying regimens, defined as an elecsys® anti-sars-cov-2 s (rbd) negative result or positive result of ≤200 u/ml, or a low immune response, defined as an elecsys® anti-sars-cov-2 s (rbd) result of ≤2500 u/ml, within 4 weeks of the stage 2 baseline/week 0 visit. the regimens of covid-19 vaccination that qualify are as follows: 1. 3 doses of the pfizer-biontech covid-19 vaccine 2. 3 doses of the moderna covid-19 vaccine 3. 2 doses of the janssen covid-19 vaccine 4. 4 or more doses of a single mrna vaccine (pfizer-biontech covid-19 vaccine or moderna covid-19 vaccine) 5. 3 or more doses of a mixture of mrna vaccines (pfizer-biontech covid-19 vaccine or moderna covid-19 vaccine) adult stage 2 (newly recruited)-specific

general adult inclusion criteria: 1. willing and able to sign informed consent 2. documented full covid-19 vaccination (cdc card or documentation in medical records) that was completed at least 4 weeks prior and no more than 52 weeks prior to the stage 1 screening visit, or if participating in stage 2, no more than 48 weeks prior to the stage 2 screening visit. general exclusion criteria 2. history of severe allergic reaction to the initial covid-19 vaccine regimen, to any component of any of the covid-19 vaccines, or to polyethylene glycol (peg). 3. new diagnosis of malignancy that will require chemotherapy or immunotherapy, or ongoing treatment for a malignancy with chemotherapy or immunotherapy. 4. active disease (per the investigator's decision) resulting in inability to hold the is therapy in the mmf/mpa or mtx arms of the study. a. the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered. 5. active disease during the screening period resulting in: an increase/addition of any is medications, or a suggestion of ms relapse per the investigator. 6. recent or current sars-cov-2 infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening). positive result on a molecular covid-19 test at screening. 8. inflammatory myocarditis/pericarditis within 6 weeks of any covid-19 vaccine doses. 9. participants with active, ongoing chronic infections. note: participants are permitted to be on chronic prophylactic antimicrobial therapy. adults with evidence of hiv, hepatitis b indicated by surface antigen, and hepatitis c indicated by anti-hepatitis c antibody positivity will be excluded. if an adult is negative for hepatitis c viral load at screening, he/she will be eligible to participate. 10. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy. note: pediatric participants on ivig therapeutically may enter the study provided they have sufficiently quiet disease that they can withhold their ivig from 8 weeks prior to the screening visit through 4 weeks after vaccination. 11. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening. 12. participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study. 13. currently pregnant or breastfeeding (for pediatric participants postmenarchal females must have a negative urine pregnancy test at screening). 15. hemoglobin (hgb) <8.0 g/dl (80 g/l) 16. past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study. 17. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of screening. 18. concurrent treatment with cyclophosphamide. adult participants taking cladribine, alemtuzumab, or mitoxantrone will also be excluded. 19. participants currently on any type of dialysis, or who have received a solid organ transplant. 20. prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness. 21. taking both mmf/mpa and mtx. 22. receiving other investigational bcdt as part of a clinical trial within 18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. 23. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening. adult general criteria inclusion criteria: individuals 18 years of age or older that meet classification criteria for systemic lupus erythematosus (sle), systemic sclerosis (ssc), rheumatoid arthritis (ra), multiple sclerosis (ms), or pemphigus participants must meet the 2019 acr/eular or 2012 slicc classification criteria for sle, the 2010 acr/eular classification criteria for ra, the 2013 eular/acr classification criteria for ssc, the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus. if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry 6. must be currently taking one of the following is medications with or without additional disease-related medications: mmf (minimum of 1000 mg per day)/mpa (minimum of 720 mg per day), mtx (minimum of 7.5mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, ofatumumab). if taking mmf/mpa or mtx, the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen. note: participants who withheld their is medications around their initial vaccinations are eligible to participate. if enrolling in the bcdt cohort, the participant must have received an anti-cd20 or an anti-cd19 bcdt in the past 18 months. 7. no changes in background is medications, including mmf/mpa or mtx, in the 4 weeks prior to screening, excluding the following: hcq, intraarticular steroids, the addition of prednisone at ≤10mg per day or prednisone at any dose when given for ≤3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted. adult general exclusion criterion 1. inability or unwillingness of a participant to give written informed consent or comply with study protocol. 14. adult female participants who are planning a pregnancy during the course of the trial. adult stage 1-specific inclusion criterion 5. negative or suboptimal serologic response to initial covid-19 vaccine regimen, defined as an elecsys® anti-sars-cov-2 s result ≤200 u/ml, at screening visit. initial covid-19 vaccine regimen is defined as either: i.2 doses of the pfizer-biontech covid-19 vaccine ii. 2 doses of the moderna covid-19 vaccine adult stage 1-specific exclusion criterion 7. receipt of a covid-19 vaccine booster prior to screening with the moderna covid-19 vaccine, pfizer-biontech covid-19 vaccine, or janssen covid-19 vaccine. adult stage 2 (newly recruited)-specific inclusion criteria 2. history of severe allergic reaction to the covid-19 vaccine, or to any component of the covid-19 vaccine, that is to be administered in stage 2, including polysorbate for participants receiving the sanofi-gsk covid-19 vaccine, or to peg. 5. negative or suboptimal serologic response to a previous covid 19 vaccine administration in one of the qualifying regimens, defined as an elecsys® anti-sars-cov-2 s (rbd) negative result or positive result of ≤200 u/ml, or a low immune response, defined as an elecsys® anti-sars-cov-2 s (rbd) result of ≤2500 u/ml, within 4 weeks of the stage 2 baseline/week 0 visit. the regimens of covid-19 vaccination that qualify are as follows: 3 doses of the pfizer-biontech covid-19 vaccine 3 doses of the moderna covid-19 vaccine 2 doses of the janssen covid-19 vaccine 4 or more doses of a single mrna vaccine (pfizer-biontech covid-19 vaccine or moderna covid-19 vaccine) 3 or more doses of a mixture of mrna vaccines (pfizer-biontech covid-19 vaccine or moderna covid-19 vaccine) adult stage 2 (newly recruited)-specific

general adult inclusion criteria: 1. willing and able to sign informed consent 2. documented full covid-19 vaccination (cdc card or documentation in medical records) that was completed at least 4 weeks prior and no more than 52 weeks prior to the stage 1 screening visit, or if participating in stage 2, no more than 48 weeks prior to the stage 2 screening visit. general exclusion criteria 2. history of severe allergic reaction to the initial covid-19 vaccine regimen, to any component of any of the covid-19 vaccines, or to polyethylene glycol (peg). 3. new diagnosis of malignancy that will require chemotherapy or immunotherapy, or ongoing treatment for a malignancy with chemotherapy or immunotherapy. 4. active disease (per the investigator's decision) resulting in inability to hold the is therapy in the mmf/mpa or mtx arms of the study. a. the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered. 5. active disease during the screening period resulting in: an increase/addition of any is medications, or a suggestion of ms relapse per the investigator. 6. recent or current sars-cov-2 infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening). positive result on a molecular covid-19 test at screening. 8. inflammatory myocarditis/pericarditis within 6 weeks of any covid-19 vaccine doses. 9. participants with active, ongoing chronic infections. note: participants are permitted to be on chronic prophylactic antimicrobial therapy. adults with evidence of hiv, hepatitis b indicated by surface antigen, and hepatitis c indicated by anti-hepatitis c antibody positivity will be excluded. if an adult is negative for hepatitis c viral load at screening, he/she will be eligible to participate. 10. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy. note: pediatric participants on ivig therapeutically may enter the study provided they have sufficiently quiet disease that they can withhold their ivig from 8 weeks prior to the screening visit through 4 weeks after vaccination. 11. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening. 12. participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study. 13. currently pregnant or breastfeeding (for pediatric participants postmenarchal females must have a negative urine pregnancy test at screening). 15. hemoglobin (hgb) <8.0 g/dl (80 g/l) 16. past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study. 17. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of screening. 18. concurrent treatment with cyclophosphamide. adult participants taking cladribine, alemtuzumab, or mitoxantrone will also be excluded. 19. participants currently on any type of dialysis, or who have received a solid organ transplant. 20. prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness. 21. taking both mmf/mpa and mtx. 22. receiving other investigational bcdt as part of a clinical trial within 18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. 23. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening. adult general criteria inclusion criteria: individuals 18 years of age or older that meet classification criteria for systemic lupus erythematosus (sle), systemic sclerosis (ssc), rheumatoid arthritis (ra), multiple sclerosis (ms), or pemphigus participants must meet the 2019 acr/eular or 2012 slicc classification criteria for sle, the 2010 acr/eular classification criteria for ra, the 2013 eular/acr classification criteria for ssc, the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus. if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry 6. must be currently taking one of the following is medications with or without additional disease-related medications: mmf (minimum of 1000 mg per day)/mpa (minimum of 720 mg per day), mtx (minimum of 7.5mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, ofatumumab). if taking mmf/mpa or mtx, the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen. note: participants who withheld their is medications around their initial vaccinations are eligible to participate. if enrolling in the bcdt cohort, the participant must have received an anti-cd20 or an anti-cd19 bcdt in the past 18 months. 7. no changes in background is medications, including mmf/mpa or mtx, in the 4 weeks prior to screening, excluding the following: hcq, intraarticular steroids, the addition of prednisone at ≤10mg per day or prednisone at any dose when given for ≤3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted. adult general exclusion criterion 1. inability or unwillingness of a participant to give written informed consent or comply with study protocol. 14. adult female participants who are planning a pregnancy during the course of the trial. adult stage 1-specific inclusion criterion 5. negative or suboptimal serologic response to initial covid-19 vaccine regimen, defined as an elecsys® anti-sars-cov-2 s result ≤200 u/ml, at screening visit. initial covid-19 vaccine regimen is defined as either: i.2 doses of the pfizer-biontech covid-19 vaccine ii. 2 doses of the moderna covid-19 vaccine adult stage 1-specific exclusion criterion 7. receipt of a covid-19 vaccine booster prior to screening with the moderna covid-19 vaccine, pfizer-biontech covid-19 vaccine, or janssen covid-19 vaccine. adult stage 2 (newly recruited)-specific inclusion criteria 2. history of severe allergic reaction to the covid-19 vaccine, or to any component of the covid-19 vaccine, that is to be administered in stage 2, including polysorbate for participants receiving the sanofi-gsk covid-19 vaccine, or to peg. 5. negative or suboptimal serologic response to a previous covid 19 vaccine administration in one of the qualifying regimens, defined as an elecsys® anti-sars-cov-2 s (rbd) negative result or positive result of ≤200 u/ml, or a low immune response, defined as an elecsys® anti-sars-cov-2 s (rbd) result of ≤2500 u/ml, within 4 weeks of the stage 2 baseline/week 0 visit. the regimens of covid-19 vaccination that qualify are as follows: 3 doses of the pfizer-biontech covid-19 vaccine 3 doses of the moderna covid-19 vaccine 2 doses of the janssen covid-19 vaccine 4 or more doses of a single mrna vaccine (pfizer-biontech covid-19 vaccine or moderna covid-19 vaccine) 3 or more doses of a mixture of mrna vaccines (pfizer-biontech covid-19 vaccine or moderna covid-19 vaccine) adult stage 2 (newly recruited)-specific

inclusion criteria adults: individuals who meet all the following criteria are eligible for enrollment as study participants- individuals that meet classification criteria for: systemic lupus erythematosus (sle) systemic sclerosis (ssc) rheumatoid arthritis (ra) multiple sclerosis (ms), or pemphigus participants must meet: the 2019 american college of rheumatology/european league against rheumatism (acr/eular) or the 2012 systemic lupus international collaborating clinics classification criteria (slicc) classification criteria for sle the 2010 acr/eular classification criteria for ra the 2013 eular/acr classification criteria for ssc the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus note: if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry willing and able to sign informed consent documented full covid-19 vaccination (e.g., centers for disease control and prevention [cdc] vaccination card or documentation in medical records) that was completed ≥ 4 weeks prior and no more than 52 weeks prior to the screening visit negative serologic or suboptimal response to initial covid-19 vaccine regimen- defined as an elecsys® anti-severe acute respiratory syndrome coronavirus-2 (anti-sars-cov-2-spike (s) protein receptor binding domain (rbd)) result ≤ 200 u/ml at screening visit -initial covid-19 vaccine regimen is defined as either: 2 doses of the pfizer-biontech covid-19 vaccine 2 doses of the moderna covid-19 vaccine, or must be currently taking one of the following is medications with or without additional disease related medications: mycophenolate mofetil (minimum of 1,000 mg per day)/mycophenolic acid (minimum of 720 mg per day) methotrexate (minimum of 7.5mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, or ofatumumab) if taking mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx), the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen participants on b cell depleting therapy may enter the study if they are also taking mmf/mpa or mtx. in this case, the mmf/mpa or mtx would not be withheld for the vaccine booster dose(s) participants taking both mmf/mpa and mtx will be excluded from the study no changes in background is medications in the 8 weeks prior to screening, excluding the following: hydroxychloroquine (hcq) intraarticular steroids the addition of prednisone at ≤10 mg per day or prednisone at any dose when given for ≤ 3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or chronic obstructive pulmonary disease (copd), are permitted exclusion criteria adults: individuals who meet any of these criteria are not eligible for enrollment as study participants- inability or unwillingness of a participant to give written informed consent or comply with study protocol history of severe allergic reaction to the initial covid-19 vaccine regimen, or any component of any of the covid-19 vaccines, or to polyethylene glycol (peg) ongoing treatment for a malignancy with chemotherapy or immunotherapy active disease (per the investigator's decision) resulting in inability to hold the immunosuppressive therapy in the mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx) arms of the study the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered active disease during the screening period resulting in: an increase/addition of immunosuppressive medications, or a suggestion of multiple sclerosis (ms) relapse per the investigator recent or current severe acute respiratory syndrome coronavirus-2 (sars-cov-2) infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening), or a positive result on a molecular covid-19 test at screening receipt of a covid-19 vaccine booster prior to screening with the moderna covid-19 vaccine, pfizer-biontech covid-19 vaccine, or janssen covid-19 vaccine participants with: a history of autoimmune disease-related myocarditis within 3 years autoimmune disease-related pericarditis within the past year, or inflammatory myocarditis/pericarditis following initial covid-19 vaccine regimen participants with active bacterial or viral infections who have received antibiotics within the 14 days prior to screening, including participants with evidence of: human immunodeficiency virus (hiv) hepatitis b as indicated by surface antigen or hepatitis b core antibody positivity hepatitis c as indicated by anti-hepatitis c antibody positivity note: if a participant is hepatitis c antibody positive, they will be eligible to participate in the study if he/she is negative for viral load at screening participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study currently pregnant or breastfeeding participants who are planning a pregnancy during the course of the trial hemoglobin (hgb) < 8.0 g/dl (80 g/l) past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator: may pose additional risks from participation in the study may interfere with the participant's ability to comply with study requirements, or that may impact the quality or interpretation of the data obtained from the study other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of enrollment concurrent treatment with cyclophosphamide, cladribine, alemtuzumab, or mitoxantrone participants currently on any type of dialysis, or who have received a solid organ transplant prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be enrolled into this study taking both mmf/mpa and mtx. receiving other investigational b cell depleting therapy as part of a clinical trial within one year18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening. inclusion criteria pediatric: individuals 5-17 years of age that meet classification criteria for sle, jia, poms, or jdm. note: juvenile idiopathic arthritis includes the following conditions: polyarticular jia (both rf + and-), oligoarticular persistent and oligoarticular extended jia, psoriatic arthritis, and enthesitis related jia. participants must meet the 2017 eular/acr classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups [8], the international league of associations for rheumatology (ilar) classification for jia [4], the 2017 mcdonald [6] criteria for ms, or the bohan and peter criteria or the 2017 eular/acr classification criteria for jdm. if a participant has been diagnosed with more than one autoimmune disease, the participant will beassessed based on the disease that is selected for study entry. parents/guardians of pediatric participants must be willing and able to sign informed consent. participants, ages 7-17, must be willing and able to sign assent. documented full covid-19 vaccination (cdc card or documentation in medical records) that was completed at least 4 weeks prior and no more than 52 weeks prior to the screening visit. negative or suboptimal serologic response to initial covid-19 vaccine regimen, defined as an elecsys® anti-sars-cov-2 s result ≤200 u/ml at screening visit. initial covid-19 vaccine regimen is defined as: - 2 doses (as appropriate to age) of the pfizer-biontech covid-19 vaccine the following vaccines have yet to receive eua in pediatric populations. if eua occurs for younger ages, the participants receiving age-appropriate regimens of the following covid-19 vaccines may be enrolled into the study: - moderna covid-19 vaccine - janssen covid-19 vaccine must be currently taking one of the following is medications with or without additional disease-related medications: mmf (minimum of 250 mg per day)/mpa (minimum of 360 mg per day), mtx (minimum of 5 mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, or ofatumumab). if taking mmf/mpa or mtx, the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen. note: participants who withheld their is medications around their initial vaccinations are eligible to participate. if enrolling in the b cell depleting therapy cohort, participant must have received an anti-cd20 or an anti-cd19 b cell depleting therapy in the past 18 months. no changes in background is medications, including mmf/mpa or mtx, in the 8 weeks prior to screening, excluding the following: hcq, intraarticular steroids, the addition of prednisone at ≤10mg per day or prednisone at any dose when given for ≤3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted. exclusion criteria pediatric: inability or unwillingness of a participant to give assent or of a parent/guardian to give written informed consent, or of either to comply with study protocol. history of severe allergic reaction to the initial covid-19 vaccine regimen, or any component of any of the covid-19 vaccines, or to peg. new diagnosis of malignancy that will require chemotherapy or immunotherapy, or ongoing treatment for a malignancy with chemotherapy or immunotherapy. active disease (per the investigator's decision) resulting in inability to hold the is therapy in the mmf/mpa or mtx arms of the study. - the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered. active disease during the screening period resulting in: an increase/addition of any is medications, or a suggestion of ms relapse per the investigator recent or current sars-cov-2 infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening). positive result on a molecular covid-19 test at screening. receipt of a covid-19 vaccine booster prior to screening. inflammatory myocarditis/pericarditis following initial covid-19 vaccine regimen. participants with active, ongoing chronic infections, including participants with evidence of: hiv. hepatitis b as indicated by surface antigen. hepatitis c as indicated by anti-hepatitis c antibody positivity; if a participant is hepatitis c antibody positive, they will be eligible to participate in the study if he/she is negative for viral load at screening. note: participants are permitted to be on chronic prophylactic antimicrobial therapy. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening. participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study. currently pregnant or breastfeeding (postmenarchal females must have a negative urine pregnancy test at screening) hemoglobin (hgb) <8.0 g/dl (80 g/l) past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of screening. concurrent treatment with cyclophosphamide. participants currently on any type of dialysis, or who have received a solid organ transplant. prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be allowed to participant in this study. taking both mmf/mpa and mtx. other investigational b cell depleting therapy as part of a clinical trial within 18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening.

inclusion criteria adults: individuals who meet all the following criteria are eligible for enrollment as study participants- individuals that meet classification criteria for: systemic lupus erythematosus (sle) systemic sclerosis (ssc) rheumatoid arthritis (ra) multiple sclerosis (ms), or pemphigus participants must meet: the 2019 american college of rheumatology/european league against rheumatism (acr/eular) or the 2012 systemic lupus international collaborating clinics classification criteria (slicc) classification criteria for sle the 2010 acr/eular classification criteria for ra the 2013 eular/acr classification criteria for ssc the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus note: if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry willing and able to sign informed consent documented full covid-19 vaccination (e.g., centers for disease control and prevention [cdc] vaccination card or documentation in medical records) that was completed ≥ 4 weeks prior and no more than 52 weeks prior to the screening visit negative serologic or suboptimal response to initial covid-19 vaccine regimen- defined as an elecsys® anti-severe acute respiratory syndrome coronavirus-2 (anti-sars-cov-2-spike (s) protein receptor binding domain (rbd)) result ≤ 200 u/ml at screening visit -initial covid-19 vaccine regimen is defined as either: 2 doses of the pfizer-biontech covid-19 vaccine 2 doses of the moderna covid-19 vaccine, or must be currently taking one of the following is medications with or without additional disease related medications: mycophenolate mofetil (minimum of 1,000 mg per day)/mycophenolic acid (minimum of 720 mg per day) methotrexate (minimum of 7.5mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, or ofatumumab) if taking mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx), the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen participants on b cell depleting therapy may enter the study if they are also taking mmf/mpa or mtx. in this case, the mmf/mpa or mtx would not be withheld for the vaccine booster dose(s) participants taking both mmf/mpa and mtx will be excluded from the study no changes in background is medications in the 8 weeks prior to screening, excluding the following: hydroxychloroquine (hcq) intraarticular steroids the addition of prednisone at ≤10 mg per day or prednisone at any dose when given for ≤ 3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or chronic obstructive pulmonary disease (copd), are permitted exclusion criteria adults: individuals who meet any of these criteria are not eligible for enrollment as study participants- inability or unwillingness of a participant to give written informed consent or comply with study protocol history of severe allergic reaction to the initial covid-19 vaccine regimen, or any component of any of the covid-19 vaccines, or to polyethylene glycol (peg) ongoing treatment for a malignancy with chemotherapy or immunotherapy active disease (per the investigator's decision) resulting in inability to hold the immunosuppressive therapy in the mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx) arms of the study the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered active disease during the screening period resulting in: an increase/addition of immunosuppressive medications, or a suggestion of multiple sclerosis (ms) relapse per the investigator recent or current severe acute respiratory syndrome coronavirus-2 (sars-cov-2) infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening), or a positive result on a molecular covid-19 test at screening receipt of a covid-19 vaccine booster prior to screening with the moderna covid-19 vaccine, pfizer-biontech covid-19 vaccine, or janssen covid-19 vaccine participants with: a history of autoimmune disease-related myocarditis within 3 years autoimmune disease-related pericarditis within the past year, or inflammatory myocarditis/pericarditis following initial covid-19 vaccine regimen participants with active bacterial or viral infections who have received antibiotics within the 14 days prior to screening, including participants with evidence of: human immunodeficiency virus (hiv) hepatitis b as indicated by surface antigen or hepatitis b core antibody positivity hepatitis c as indicated by anti-hepatitis c antibody positivity note: if a participant is hepatitis c antibody positive, they will be eligible to participate in the study if he/she is negative for viral load at screening participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study currently pregnant or breastfeeding participants who are planning a pregnancy during the course of the trial hemoglobin (hgb) < 8.0 g/dl (80 g/l) past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator: may pose additional risks from participation in the study may interfere with the participant's ability to comply with study requirements, or that may impact the quality or interpretation of the data obtained from the study other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of enrollment concurrent treatment with cyclophosphamide, cladribine, alemtuzumab, or mitoxantrone participants currently on any type of dialysis, or who have received a solid organ transplant prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be enrolled into this study taking both mmf/mpa and mtx. receiving other investigational b cell depleting therapy as part of a clinical trial within one year18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening. inclusion criteria pediatric: individuals 5-17 years of age that meet classification criteria for sle, jia, poms, or jdm. note: juvenile idiopathic arthritis includes the following conditions: polyarticular jia (both rf + and-), oligoarticular persistent and oligoarticular extended jia, psoriatic arthritis, and enthesitis related jia. participants must meet the 2017 eular/acr classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups [8], the international league of associations for rheumatology (ilar) classification for jia [4], the 2017 mcdonald [6] criteria for ms, or the bohan and peter criteria or the 2017 eular/acr classification criteria for jdm. if a participant has been diagnosed with more than one autoimmune disease, the participant will beassessed based on the disease that is selected for study entry. parents/guardians of pediatric participants must be willing and able to sign informed consent. participants, ages 7-17, must be willing and able to sign assent. documented full covid-19 vaccination (cdc card or documentation in medical records) that was completed at least 4 weeks prior and no more than 52 weeks prior to the screening visit. negative or suboptimal serologic response to initial covid-19 vaccine regimen, defined as an elecsys® anti-sars-cov-2 s result ≤200 u/ml at screening visit. initial covid-19 vaccine regimen is defined as: - 2 doses (as appropriate to age) of the pfizer-biontech covid-19 vaccine the following vaccines have yet to receive eua in pediatric populations. if eua occurs for younger ages, the participants receiving age-appropriate regimens of the following covid-19 vaccines may be enrolled into the study: - moderna covid-19 vaccine - janssen covid-19 vaccine must be currently taking one of the following is medications with or without additional disease-related medications: mmf (minimum of 250 mg per day)/mpa (minimum of 360 mg per day), mtx (minimum of 5 mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, or ofatumumab). if taking mmf/mpa or mtx, the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen. note: participants who withheld their is medications around their initial vaccinations are eligible to participate. if enrolling in the b cell depleting therapy cohort, participant must have received an anti-cd20 or an anti-cd19 b cell depleting therapy in the past 18 months. no changes in background is medications, including mmf/mpa or mtx, in the 8 weeks prior to screening, excluding the following: hcq, intraarticular steroids, the addition of prednisone at ≤10mg per day or prednisone at any dose when given for ≤3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted. exclusion criteria pediatric: inability or unwillingness of a participant to give assent or of a parent/guardian to give written informed consent, or of either to comply with study protocol. history of severe allergic reaction to the initial covid-19 vaccine regimen, or any component of any of the covid-19 vaccines, or to peg. new diagnosis of malignancy that will require chemotherapy or immunotherapy, or ongoing treatment for a malignancy with chemotherapy or immunotherapy. active disease (per the investigator's decision) resulting in inability to hold the is therapy in the mmf/mpa or mtx arms of the study. - the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered. active disease during the screening period resulting in: an increase/addition of any is medications, or a suggestion of ms relapse per the investigator recent or current sars-cov-2 infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening). positive result on a molecular covid-19 test at screening. receipt of a covid-19 vaccine booster prior to screening. inflammatory myocarditis/pericarditis following initial covid-19 vaccine regimen. participants with active, ongoing chronic infections, including participants with evidence of: hiv. hepatitis b as indicated by surface antigen. hepatitis c as indicated by anti-hepatitis c antibody positivity; if a participant is hepatitis c antibody positive, they will be eligible to participate in the study if he/she is negative for viral load at screening. note: participants are permitted to be on chronic prophylactic antimicrobial therapy. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening. participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study. currently pregnant or breastfeeding (postmenarchal females must have a negative urine pregnancy test at screening) hemoglobin (hgb) <8.0 g/dl (80 g/l) past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of screening. concurrent treatment with cyclophosphamide. participants currently on any type of dialysis, or who have received a solid organ transplant. prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be allowed to participant in this study. taking both mmf/mpa and mtx. other investigational b cell depleting therapy as part of a clinical trial within 18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening.

None

None

inclusion criteria adults: individuals who meet all the following criteria are eligible for enrollment as study participants- individuals that meet classification criteria for: systemic lupus erythematosus (sle) systemic sclerosis (ssc) rheumatoid arthritis (ra) multiple sclerosis (ms), or pemphigus participants must meet: the 2019 american college of rheumatology/european league against rheumatism (acr/eular) or the 2012 systemic lupus international collaborating clinics classification criteria (slicc) classification criteria for sle the 2010 acr/eular classification criteria for ra the 2013 eular/acr classification criteria for ssc the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus note: if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry willing and able to sign informed consent documented full covid-19 vaccination (e.g., centers for disease control and prevention [cdc] vaccination card or documentation in medical records) that was completed ≥ 4 weeks prior and no more than 52 weeks prior to the screening visit negative serologic or suboptimal response to initial covid-19 vaccine regimen- defined as an elecsys® anti-severe acute respiratory syndrome coronavirus-2 (anti-sars-cov-2-spike (s) protein receptor binding domain (rbd)) result ≤ 200 u/ml at screening visit -initial covid-19 vaccine regimen is defined as either: 2 doses of the pfizer-biontech covid-19 vaccine 2 doses of the moderna covid-19 vaccine, or must be currently taking one of the following is medications with or without additional disease related medications: mycophenolate mofetil (minimum of 1,000 mg per day)/mycophenolic acid (minimum of 720 mg per day) methotrexate (minimum of 7.5mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, or ofatumumab) if taking mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx), the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen participants on b cell depleting therapy may enter the study if they are also taking mmf/mpa or mtx. in this case, the mmf/mpa or mtx would not be withheld for the vaccine booster dose(s) participants taking both mmf/mpa and mtx will be excluded from the study no changes in background is medications in the 8 weeks prior to screening, excluding the following: hydroxychloroquine (hcq) intraarticular steroids the addition of prednisone at ≤10 mg per day or prednisone at any dose when given for ≤ 3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or chronic obstructive pulmonary disease (copd), are permitted exclusion criteria adults: individuals who meet any of these criteria are not eligible for enrollment as study participants- inability or unwillingness of a participant to give written informed consent or comply with study protocol history of severe allergic reaction to the initial covid-19 vaccine regimen, or any component of any of the covid-19 vaccines, or to polyethylene glycol (peg) ongoing treatment for a malignancy with chemotherapy or immunotherapy active disease (per the investigator's decision) resulting in inability to hold the immunosuppressive therapy in the mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx) arms of the study the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered active disease during the screening period resulting in: an increase/addition of immunosuppressive medications, or a suggestion of multiple sclerosis (ms) relapse per the investigator recent or current severe acute respiratory syndrome coronavirus-2 (sars-cov-2) infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening), or a positive result on a molecular covid-19 test at screening receipt of a covid-19 vaccine booster prior to screening with the moderna covid-19 vaccine, pfizer-biontech covid-19 vaccine, or janssen covid-19 vaccine participants with: a history of autoimmune disease-related myocarditis within 3 years autoimmune disease-related pericarditis within the past year, or inflammatory myocarditis/pericarditis following initial covid-19 vaccine regimen participants with active bacterial or viral infections who have received antibiotics within the 14 days prior to screening, including participants with evidence of: human immunodeficiency virus (hiv) hepatitis b as indicated by surface antigen or hepatitis b core antibody positivity hepatitis c as indicated by anti-hepatitis c antibody positivity note: if a participant is hepatitis c antibody positive, they will be eligible to participate in the study if he/she is negative for viral load at screening participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study currently pregnant or breastfeeding participants who are planning a pregnancy during the course of the trial hemoglobin (hgb) < 8.0 g/dl (80 g/l) past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator: may pose additional risks from participation in the study may interfere with the participant's ability to comply with study requirements, or that may impact the quality or interpretation of the data obtained from the study other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of enrollment concurrent treatment with cyclophosphamide, cladribine, alemtuzumab, or mitoxantrone participants currently on any type of dialysis, or who have received a solid organ transplant prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be enrolled into this study taking both mmf/mpa and mtx. receiving other investigational b cell depleting therapy as part of a clinical trial within one year18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening. inclusion criteria pediatric: individuals 5-17 years of age that meet classification criteria for sle, jia, poms, or jdm. note: juvenile idiopathic arthritis includes the following conditions: polyarticular jia (both rf + and-), oligoarticular persistent and oligoarticular extended jia, psoriatic arthritis, and enthesitis related jia. participants must meet the 2017 eular/acr classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups [8], the international league of associations for rheumatology (ilar) classification for jia [4], the 2017 mcdonald [6] criteria for ms, or the bohan and peter criteria or the 2017 eular/acr classification criteria for jdm. if a participant has been diagnosed with more than one autoimmune disease, the participant will beassessed based on the disease that is selected for study entry. parents/guardians of pediatric participants must be willing and able to sign informed consent. participants, ages 7-17, must be willing and able to sign assent. documented full covid-19 vaccination (cdc card or documentation in medical records) that was completed at least 4 weeks prior and no more than 52 weeks prior to the screening visit. negative or suboptimal serologic response to initial covid-19 vaccine regimen, defined as an elecsys® anti-sars-cov-2 s result ≤200 u/ml at screening visit. initial covid-19 vaccine regimen is defined as: - 2 doses (as appropriate to age) of the pfizer-biontech covid-19 vaccine the following vaccines have yet to receive eua in pediatric populations. if eua occurs for younger ages, the participants receiving age-appropriate regimens of the following covid-19 vaccines may be enrolled into the study: - moderna covid-19 vaccine - janssen covid-19 vaccine must be currently taking one of the following is medications with or without additional disease-related medications: mmf (minimum of 250 mg per day)/mpa (minimum of 360 mg per day), mtx (minimum of 5 mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, or ofatumumab). if taking mmf/mpa or mtx, the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen. note: participants who withheld their is medications around their initial vaccinations are eligible to participate. if enrolling in the b cell depleting therapy cohort, participant must have received an anti-cd20 or an anti-cd19 b cell depleting therapy in the past 18 months. no changes in background is medications, including mmf/mpa or mtx, in the 8 weeks prior to screening, excluding the following: hcq, intraarticular steroids, the addition of prednisone at ≤10mg per day or prednisone at any dose when given for ≤3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted. exclusion criteria pediatric: inability or unwillingness of a participant to give assent or of a parent/guardian to give written informed consent, or of either to comply with study protocol. history of severe allergic reaction to the initial covid-19 vaccine regimen, or any component of any of the covid-19 vaccines, or to peg. new diagnosis of malignancy that will require chemotherapy or immunotherapy, or ongoing treatment for a malignancy with chemotherapy or immunotherapy. active disease (per the investigator's decision) resulting in inability to hold the is therapy in the mmf/mpa or mtx arms of the study. - the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered. active disease during the screening period resulting in: an increase/addition of any is medications, or a suggestion of ms relapse per the investigator recent or current sars-cov-2 infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening). positive result on a molecular covid-19 test at screening. receipt of a covid-19 vaccine booster prior to screening. inflammatory myocarditis/pericarditis following initial covid-19 vaccine regimen. participants with active, ongoing chronic infections, including participants with evidence of: hiv. hepatitis b as indicated by surface antigen. hepatitis c as indicated by anti-hepatitis c antibody positivity; if a participant is hepatitis c antibody positive, they will be eligible to participate in the study if he/she is negative for viral load at screening. note: participants are permitted to be on chronic prophylactic antimicrobial therapy. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening. participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study. currently pregnant or breastfeeding (postmenarchal females must have a negative urine pregnancy test at screening) hemoglobin (hgb) <8.0 g/dl (80 g/l) past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of screening. concurrent treatment with cyclophosphamide. participants currently on any type of dialysis, or who have received a solid organ transplant. prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be allowed to participant in this study. taking both mmf/mpa and mtx. other investigational b cell depleting therapy as part of a clinical trial within 18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening.

inclusion criteria adults: individuals who meet all the following criteria are eligible for enrollment as study participants- individuals that meet classification criteria for: systemic lupus erythematosus (sle) systemic sclerosis (ssc) rheumatoid arthritis (ra) multiple sclerosis (ms), or pemphigus participants must meet: the 2019 american college of rheumatology/european league against rheumatism (acr/eular) or the 2012 systemic lupus international collaborating clinics classification criteria (slicc) classification criteria for sle the 2010 acr/eular classification criteria for ra the 2013 eular/acr classification criteria for ssc the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus note: if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry willing and able to sign informed consent documented full covid-19 vaccination (e.g., centers for disease control and prevention [cdc] vaccination card or documentation in medical records) that was completed ≥ 4 weeks prior and no more than 52 weeks prior to the screening visit negative serologic or suboptimal response to initial covid-19 vaccine regimen- defined as an elecsys® anti-severe acute respiratory syndrome coronavirus-2 (anti-sars-cov-2-spike (s) protein receptor binding domain (rbd)) result ≤ 200 u/ml at screening visit -initial covid-19 vaccine regimen is defined as either: 2 doses of the pfizer-biontech covid-19 vaccine 2 doses of the moderna covid-19 vaccine, or must be currently taking one of the following is medications with or without additional disease related medications: mycophenolate mofetil (minimum of 1,000 mg per day)/mycophenolic acid (minimum of 720 mg per day) methotrexate (minimum of 7.5mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, or ofatumumab) if taking mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx), the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen participants on b cell depleting therapy may enter the study if they are also taking mmf/mpa or mtx. in this case, the mmf/mpa or mtx would not be withheld for the vaccine booster dose(s) participants taking both mmf/mpa and mtx will be excluded from the study no changes in background is medications in the 8 weeks prior to screening, excluding the following: hydroxychloroquine (hcq) intraarticular steroids the addition of prednisone at ≤10 mg per day or prednisone at any dose when given for ≤ 3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or chronic obstructive pulmonary disease (copd), are permitted exclusion criteria adults: individuals who meet any of these criteria are not eligible for enrollment as study participants- inability or unwillingness of a participant to give written informed consent or comply with study protocol history of severe allergic reaction to the initial covid-19 vaccine regimen, or any component of any of the covid-19 vaccines, or to polyethylene glycol (peg) ongoing treatment for a malignancy with chemotherapy or immunotherapy active disease (per the investigator's decision) resulting in inability to hold the immunosuppressive therapy in the mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx) arms of the study the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered active disease during the screening period resulting in: an increase/addition of immunosuppressive medications, or a suggestion of multiple sclerosis (ms) relapse per the investigator recent or current severe acute respiratory syndrome coronavirus-2 (sars-cov-2) infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening), or a positive result on a molecular covid-19 test at screening receipt of a covid-19 vaccine booster prior to screening with the moderna covid-19 vaccine, pfizer-biontech covid-19 vaccine, or janssen covid-19 vaccine participants with: a history of autoimmune disease-related myocarditis within 3 years autoimmune disease-related pericarditis within the past year, or inflammatory myocarditis/pericarditis following initial covid-19 vaccine regimen participants with active bacterial or viral infections who have received antibiotics within the 14 days prior to screening, including participants with evidence of: human immunodeficiency virus (hiv) hepatitis b as indicated by surface antigen or hepatitis b core antibody positivity hepatitis c as indicated by anti-hepatitis c antibody positivity note: if a participant is hepatitis c antibody positive, they will be eligible to participate in the study if he/she is negative for viral load at screening participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study currently pregnant or breastfeeding participants who are planning a pregnancy during the course of the trial hemoglobin (hgb) < 8.0 g/dl (80 g/l) past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator: may pose additional risks from participation in the study may interfere with the participant's ability to comply with study requirements, or that may impact the quality or interpretation of the data obtained from the study other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of enrollment concurrent treatment with cyclophosphamide, cladribine, alemtuzumab, or mitoxantrone participants currently on any type of dialysis, or who have received a solid organ transplant prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be enrolled into this study taking both mmf/mpa and mtx. receiving other investigational b cell depleting therapy as part of a clinical trial within one year18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening. inclusion criteria pediatric: individuals 5-17 years of age that meet classification criteria for sle, jia, poms, or jdm. note: juvenile idiopathic arthritis includes the following conditions: polyarticular jia (both rf + and-), oligoarticular persistent and oligoarticular extended jia, psoriatic arthritis, and enthesitis related jia. participants must meet the 2017 eular/acr classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups [8], the international league of associations for rheumatology (ilar) classification for jia [4], the 2017 mcdonald [6] criteria for ms, or the bohan and peter criteria or the 2017 eular/acr classification criteria for jdm. if a participant has been diagnosed with more than one autoimmune disease, the participant will beassessed based on the disease that is selected for study entry. parents/guardians of pediatric participants must be willing and able to sign informed consent. participants, ages 7-17, must be willing and able to sign assent. documented full covid-19 vaccination (cdc card or documentation in medical records) that was completed at least 4 weeks prior and no more than 52 weeks prior to the screening visit. negative or suboptimal serologic response to initial covid-19 vaccine regimen, defined as an elecsys® anti-sars-cov-2 s result ≤200 u/ml at screening visit. initial covid-19 vaccine regimen is defined as: - 2 doses (as appropriate to age) of the pfizer-biontech covid-19 vaccine the following vaccines have yet to receive eua in pediatric populations. if eua occurs for younger ages, the participants receiving age-appropriate regimens of the following covid-19 vaccines may be enrolled into the study: - moderna covid-19 vaccine - janssen covid-19 vaccine must be currently taking one of the following is medications with or without additional disease-related medications: mmf (minimum of 250 mg per day)/mpa (minimum of 360 mg per day), mtx (minimum of 5 mg per week), or b cell depleting agents within the past 18 months (such as rituximab, ocrelizumab, or ofatumumab). if taking mmf/mpa or mtx, the participant must have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen. note: participants who withheld their is medications around their initial vaccinations are eligible to participate. if enrolling in the b cell depleting therapy cohort, participant must have received an anti-cd20 or an anti-cd19 b cell depleting therapy in the past 18 months. no changes in background is medications, including mmf/mpa or mtx, in the 8 weeks prior to screening, excluding the following: hcq, intraarticular steroids, the addition of prednisone at ≤10mg per day or prednisone at any dose when given for ≤3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted. exclusion criteria pediatric: inability or unwillingness of a participant to give assent or of a parent/guardian to give written informed consent, or of either to comply with study protocol. history of severe allergic reaction to the initial covid-19 vaccine regimen, or any component of any of the covid-19 vaccines, or to peg. new diagnosis of malignancy that will require chemotherapy or immunotherapy, or ongoing treatment for a malignancy with chemotherapy or immunotherapy. active disease (per the investigator's decision) resulting in inability to hold the is therapy in the mmf/mpa or mtx arms of the study. - the potential impact of temporarily holding medication for participants with a recent mild disease flare within 4 weeks should be carefully considered. active disease during the screening period resulting in: an increase/addition of any is medications, or a suggestion of ms relapse per the investigator recent or current sars-cov-2 infection defined as: documented sars-cov-2 infection in the past 30 days (from the day the participant is diagnosed by positive test to screening). positive result on a molecular covid-19 test at screening. receipt of a covid-19 vaccine booster prior to screening. inflammatory myocarditis/pericarditis following initial covid-19 vaccine regimen. participants with active, ongoing chronic infections, including participants with evidence of: hiv. hepatitis b as indicated by surface antigen. hepatitis c as indicated by anti-hepatitis c antibody positivity; if a participant is hepatitis c antibody positive, they will be eligible to participate in the study if he/she is negative for viral load at screening. note: participants are permitted to be on chronic prophylactic antimicrobial therapy. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 30 days of screening. participants who have received any live vaccines within 2 months of the anticipated study vaccine dose or who will have need of a live vaccine at any time during the study. currently pregnant or breastfeeding (postmenarchal females must have a negative urine pregnancy test at screening) hemoglobin (hgb) <8.0 g/dl (80 g/l) past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of screening. concurrent treatment with cyclophosphamide. participants currently on any type of dialysis, or who have received a solid organ transplant. prisoners or participants who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be allowed to participant in this study. taking both mmf/mpa and mtx. other investigational b cell depleting therapy as part of a clinical trial within 18 months of screening, unless drug assignment is known and the participant received an anti-cd20 or cd19 drug. participants with active systemic infections who have received systemic antimicrobials within the 14 days prior to screening.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- individuals that meet classification criteria for: systemic lupus erythematosus (sle) systemic sclerosis (ssc) rheumatoid arthritis (ra) multiple sclerosis (ms), or pemphigus participants must meet: the 2019 american college of rheumatology/european league against rheumatism (acr/eular) or the 2012 systemic lupus international collaborating clinics classification criteria (slicc) classification criteria for sle the 2010 acr/eular classification criteria for ra the 2013 eular/acr classification criteria for ssc the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus note: if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry willing and able to sign informed consent documented full covid-19 vaccination (e.g., centers for disease control and prevention [cdc] vaccination card or documentation in medical records) that was completed ≥ 4 weeks prior and no more than 36 weeks prior to the screening visit negative serologic or suboptimal response to initial covid-19 vaccine regimen- defined as an elecsys® anti-severe acute respiratory syndrome coronavirus-2 (anti-sars-cov-2-spike (s) protein receptor binding domain (rbd)) result ≤ 50 u/ml at screening visit -initial covid-19 vaccine regimen is defined as either: 2 doses of the pfizer-biontech covid-19 vaccine 2 doses of the moderna covid-19 vaccine, or a single dose of the janssen covid-19 vaccine must be currently taking one of the following immunosuppressive medications with or without additional disease related medications: mycophenolate mofetil (minimum of 1,000 mg per day)/mycophenolic acid (minimum of 720 mg per day) methotrexate (minimum of 7.5mg per week), or b cell depleting agents within the past 12 months (such as rituximab, ocrelizumab, ofatumumab) if taking mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx), the participant should have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen participants on b cell depleting therapy may enter the study if they are also taking mmf/mpa or mtx. in this case, the mmf/mpa or mtx would not be withheld for the vaccine booster dose(s) participants taking both mmf/mpa and mtx will be excluded from the study no changes in background immunosuppressive medications in the 8 weeks prior to screening, excluding the following: hydroxychloroquine (hcq) intraarticular steroids the addition of prednisone at ≤10 mg per day or prednisone at any dose when given for ≤ 3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or chronic obstructive pulmonary disease (copd), are permitted

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- individuals that meet classification criteria for: systemic lupus erythematosus (sle) systemic sclerosis (ssc) rheumatoid arthritis (ra) multiple sclerosis (ms), or pemphigus participants must meet: the 2019 american college of rheumatology/european league against rheumatism (acr/eular) or the 2012 systemic lupus international collaborating clinics classification criteria (slicc) classification criteria for sle the 2010 acr/eular classification criteria for ra the 2013 eular/acr classification criteria for ssc the 2017 mcdonald criteria for ms, and the international consensus criteria for pemphigus note: if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry willing and able to sign informed consent documented full covid-19 vaccination (e.g., centers for disease control and prevention [cdc] vaccination card or documentation in medical records) that was completed ≥ 4 weeks prior and no more than 36 weeks prior to the screening visit negative serologic or suboptimal response to initial covid-19 vaccine regimen- defined as an elecsys® anti-severe acute respiratory syndrome coronavirus-2 (anti-sars-cov-2-spike (s) protein receptor binding domain (rbd)) result ≤ 50 u/ml at screening visit -initial covid-19 vaccine regimen is defined as either: 2 doses of the pfizer-biontech covid-19 vaccine 2 doses of the moderna covid-19 vaccine, or a single dose of the janssen covid-19 vaccine must be currently taking one of the following immunosuppressive medications with or without additional disease related medications: mycophenolate mofetil (minimum of 1,000 mg per day)/mycophenolic acid (minimum of 720 mg per day) methotrexate (minimum of 7.5mg per week), or b cell depleting agents within the past 12 months (such as rituximab, ocrelizumab, ofatumumab) if taking mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx), the participant should have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen participants on b cell depleting therapy may enter the study if they are also taking mmf/mpa or mtx. in this case, the mmf/mpa or mtx would not be withheld for the vaccine booster dose(s) participants taking both mmf/mpa and mtx will be excluded from the study no changes in background immunosuppressive medications in the 8 weeks prior to screening, excluding the following: hydroxychloroquine (hcq) intraarticular steroids the addition of prednisone at ≤10 mg per day or prednisone at any dose when given for ≤ 3 days, and corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or chronic obstructive pulmonary disease (copd), are permitted

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- 1. individuals that meet classification criteria for: - systemic lupus erythematosus (sle) - systemic sclerosis (ssc) - rheumatoid arthritis (ra) - multiple sclerosis (ms), or - pemphigus 2. participants must meet: - the 2019 american college of rheumatology/european league against rheumatism (acr/eular) or the 2012 systemic lupus international collaborating clinics classification criteria (slicc) classification criteria for sle - the 2010 acr/eular classification criteria for ra - the 2013 eular/acr classification criteria for ssc - the 2017 mcdonald criteria for ms, and - the international consensus criteria for pemphigus note: if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry 3. willing and able to sign informed consent 4. documented full covid-19 vaccination (e.g., centers for disease control and prevention [cdc] vaccination card or documentation in medical records) that was completed ≥ 4 weeks prior and no more than 36 weeks prior to the screening visit 5. negative serologic or suboptimal response to initial covid-19 vaccine regimen- defined as an elecsys® anti-severe acute respiratory syndrome coronavirus-2 (anti-sars-cov-2-spike (s) protein receptor binding domain (rbd)) result ≤ 50 u/ml at screening visit -initial covid-19 vaccine regimen is defined as either: - 2 doses of the pfizer-biontech covid-19 vaccine - 2 doses of the moderna covid-19 vaccine, or - a single dose of the janssen covid-19 vaccine 6. must be currently taking one of the following immunosuppressive medications with or without additional disease related medications: - mycophenolate mofetil (minimum of 1,000 mg per day)/mycophenolic acid (minimum of 720 mg per day) - methotrexate (minimum of 7.5mg per week), or - b cell depleting agents within the past 12 months (such as rituximab, ocrelizumab, ofatumumab) - if taking mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx), the participant should have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen - participants on b cell depleting therapy may enter the study if they are also taking mmf/mpa or mtx. in this case, the mmf/mpa or mtx would not be withheld for the vaccine booster dose(s) - participants taking both mmf/mpa and mtx will be excluded from the study 7. no changes in background immunosuppressive medications in the 8 weeks prior to screening, excluding the following: - hydroxychloroquine (hcq) - intraarticular steroids - the addition of prednisone at ≤10 mg per day or prednisone at any dose when given for ≤ 3 days, and - corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or chronic obstructive pulmonary disease (copd), are permitted

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- 1. individuals that meet classification criteria for: - systemic lupus erythematosus (sle) - systemic sclerosis (ssc) - rheumatoid arthritis (ra) - multiple sclerosis (ms), or - pemphigus 2. participants must meet: - the 2019 american college of rheumatology/european league against rheumatism (acr/eular) or the 2012 systemic lupus international collaborating clinics classification criteria (slicc) classification criteria for sle - the 2010 acr/eular classification criteria for ra - the 2013 eular/acr classification criteria for ssc - the 2017 mcdonald criteria for ms, and - the international consensus criteria for pemphigus note: if a participant has been diagnosed with more than one autoimmune disease, the participant will be assessed based on the disease that is selected for study entry 3. willing and able to sign informed consent 4. documented full covid-19 vaccination (e.g., centers for disease control and prevention [cdc] vaccination card or documentation in medical records) that was completed ≥ 4 weeks prior and no more than 36 weeks prior to the screening visit 5. negative serologic or suboptimal response to initial covid-19 vaccine regimen- defined as an elecsys® anti-severe acute respiratory syndrome coronavirus-2 (anti-sars-cov-2-spike (s) protein receptor binding domain (rbd)) result ≤ 50 u/ml at screening visit -initial covid-19 vaccine regimen is defined as either: - 2 doses of the pfizer-biontech covid-19 vaccine - 2 doses of the moderna covid-19 vaccine, or - a single dose of the janssen covid-19 vaccine 6. must be currently taking one of the following immunosuppressive medications with or without additional disease related medications: - mycophenolate mofetil (minimum of 1,000 mg per day)/mycophenolic acid (minimum of 720 mg per day) - methotrexate (minimum of 7.5mg per week), or - b cell depleting agents within the past 12 months (such as rituximab, ocrelizumab, ofatumumab) - if taking mycophenolate mofetil (mmf)/mycophenolic acid (mpa) or methotrexate (mtx), the participant should have initiated therapy at least 8 weeks prior to randomization and be taking the same medications (regardless of dose) as at the time of the initial covid-19 vaccine regimen - participants on b cell depleting therapy may enter the study if they are also taking mmf/mpa or mtx. in this case, the mmf/mpa or mtx would not be withheld for the vaccine booster dose(s) - participants taking both mmf/mpa and mtx will be excluded from the study 7. no changes in background immunosuppressive medications in the 8 weeks prior to screening, excluding the following: - hydroxychloroquine (hcq) - intraarticular steroids - the addition of prednisone at ≤10 mg per day or prednisone at any dose when given for ≤ 3 days, and - corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or chronic obstructive pulmonary disease (copd), are permitted