7. receipt of a mixture of janssen covid-19 vaccines and mrna covid-19 vaccines (in any order or combination) prior to stage 2 screening. adult stage 2 (rollover)-specific inclusion criteria: individuals who were previously enrolled in adult stage 1 or adult stage 2 will have met some inclusion and exclusion criteria at that time. only a subset of the criteria for (re-)entering adult stage 2 will be assessed in rollover participants at the time of screening for stage 2. individuals who meet all of the following criteria are eligible to (re )enter adult stage 2: 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: a. 3 doses of the pfizer-biontech covid-19 vaccine b. 3 doses of the moderna covid-19 vaccine c. 2 doses of the janssen covid-19 vaccine d. 4 doses of a combination of mrna vaccines (i.e., pfizer-biontech covid-19 vaccine, moderna covid-19 vaccine) general pediatric inclusion criteria 1. individuals 2-17 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. 1. participants must meet the 2017 eular/acr classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups, the international league of associations for rheumatology (ilar) classification for jia, the 2017 mcdonald criteria for ms, or the bohan and peter criteria or the 2017 eular/acr classification criteria for jdm. 2. 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. 2. parents/guardians of all pediatric participants and participants ages 14 - 17 must be willing and able to sign informed consent. participants ages 7-13 must be willing and able to sign assent. 5. 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). 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, participant must have received an anti-cd20 or an anti-cd19 bcdt in the past 18 months. 6. no changes in background is medications, including mmf/mpa or mtx, in the 8 weeks prior to screening, excluding the following: a. hcq, b. intraarticular steroids, c. the addition of prednisone at \<0.15mg/kg/dose per day or prednisone at any dose when given for ≤3 days, and d. corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted general pediatric exclusion criteria 1. 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. pediatric stage 1-specific inclusion criteria: 4. negative or suboptimal serologic response to initial eua-authorized or fda-approved covid-19 vaccine doses, defined as an elecsys® anti-sars-cov-2 s result ≤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 1 baseline/week 0 visit initial covid-19 vaccine regimen is defined as: i. pfizer-biontech covid-19 vaccine (2 through 4 years of age): 3 age-appropriate doses ii. pfizer-biontech covid-19 vaccine (5 through 17 years of age): 2 age-appropriate doses iii. moderna covid-19 vaccine (2 through 17 years of age): 2 age-appropriate doses. pediatric stage 1-specific

7. receipt of a mixture of janssen covid-19 vaccines and mrna covid-19 vaccines (in any order or combination) prior to stage 2 screening. adult stage 2 (rollover)-specific inclusion criteria: individuals who were previously enrolled in adult stage 1 or adult stage 2 will have met some inclusion and exclusion criteria at that time. only a subset of the criteria for (re-)entering adult stage 2 will be assessed in rollover participants at the time of screening for stage 2. individuals who meet all of the following criteria are eligible to (re )enter adult stage 2: 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: a. 3 doses of the pfizer-biontech covid-19 vaccine b. 3 doses of the moderna covid-19 vaccine c. 2 doses of the janssen covid-19 vaccine d. 4 doses of a combination of mrna vaccines (i.e., pfizer-biontech covid-19 vaccine, moderna covid-19 vaccine) general pediatric inclusion criteria 1. individuals 2-17 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. 1. participants must meet the 2017 eular/acr classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups, the international league of associations for rheumatology (ilar) classification for jia, the 2017 mcdonald criteria for ms, or the bohan and peter criteria or the 2017 eular/acr classification criteria for jdm. 2. 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. 2. parents/guardians of all pediatric participants and participants ages 14 - 17 must be willing and able to sign informed consent. participants ages 7-13 must be willing and able to sign assent. 5. 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). 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, participant must have received an anti-cd20 or an anti-cd19 bcdt in the past 18 months. 6. no changes in background is medications, including mmf/mpa or mtx, in the 8 weeks prior to screening, excluding the following: a. hcq, b. intraarticular steroids, c. the addition of prednisone at \<0.15mg/kg/dose per day or prednisone at any dose when given for ≤3 days, and d. corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted general pediatric exclusion criteria 1. 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. pediatric stage 1-specific inclusion criteria: 4. negative or suboptimal serologic response to initial eua-authorized or fda-approved covid-19 vaccine doses, defined as an elecsys® anti-sars-cov-2 s result ≤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 1 baseline/week 0 visit initial covid-19 vaccine regimen is defined as: i. pfizer-biontech covid-19 vaccine (2 through 4 years of age): 3 age-appropriate doses ii. pfizer-biontech covid-19 vaccine (5 through 17 years of age): 2 age-appropriate doses iii. moderna covid-19 vaccine (2 through 17 years of age): 2 age-appropriate doses. pediatric stage 1-specific

7. receipt of a mixture of janssen covid-19 vaccines and mrna covid-19 vaccines (in any order or combination) prior to stage 2 screening. adult stage 2 (rollover)-specific inclusion criteria: individuals who were previously enrolled in adult stage 1 or adult stage 2 will have met some inclusion and exclusion criteria at that time. only a subset of the criteria for (re-)entering adult stage 2 will be assessed in rollover participants at the time of screening for stage 2. individuals who meet all of the following criteria are eligible to (re )enter adult stage 2: 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: a. 3 doses of the pfizer-biontech covid-19 vaccine b. 3 doses of the moderna covid-19 vaccine c. 2 doses of the janssen covid-19 vaccine d. 4 doses of a combination of mrna vaccines (i.e., pfizer-biontech covid-19 vaccine, moderna covid-19 vaccine) general pediatric inclusion criteria individuals 2-17 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, the international league of associations for rheumatology (ilar) classification for jia, the 2017 mcdonald 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 be assessed based on the disease that is selected for study entry. parents/guardians of all pediatric participants and participants ages 14 - 17 must be willing and able to sign informed consent. participants ages 7-13 must be willing and able to sign assent. 5. 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 bcdt cohort, participant must have received an anti-cd20 or an anti-cd19 bcdt in the past 18 months. 6. no changes in background is medications, including mmf/mpa or mtx, in the 8 weeks prior to screening, excluding the following: a. hcq, b. intraarticular steroids, c. the addition of prednisone at <0.15mg/kg/dose per day or prednisone at any dose when given for ≤3 days, and d. corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted general pediatric exclusion criteria 1. 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. pediatric stage 1-specific inclusion criteria: 4. negative or suboptimal serologic response to initial eua-authorized or fda-approved covid-19 vaccine doses, defined as an elecsys® anti-sars-cov-2 s result ≤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 1 baseline/week 0 visit initial covid-19 vaccine regimen is defined as: i. pfizer-biontech covid-19 vaccine (2 through 4 years of age): 3 age-appropriate doses ii. pfizer-biontech covid-19 vaccine (5 through 17 years of age): 2 age-appropriate doses iii. moderna covid-19 vaccine (2 through 17 years of age): 2 age-appropriate doses. pediatric stage 1-specific

7. receipt of a mixture of janssen covid-19 vaccines and mrna covid-19 vaccines (in any order or combination) prior to stage 2 screening. adult stage 2 (rollover)-specific inclusion criteria: individuals who were previously enrolled in adult stage 1 or adult stage 2 will have met some inclusion and exclusion criteria at that time. only a subset of the criteria for (re-)entering adult stage 2 will be assessed in rollover participants at the time of screening for stage 2. individuals who meet all of the following criteria are eligible to (re )enter adult stage 2: 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: a. 3 doses of the pfizer-biontech covid-19 vaccine b. 3 doses of the moderna covid-19 vaccine c. 2 doses of the janssen covid-19 vaccine d. 4 doses of a combination of mrna vaccines (i.e., pfizer-biontech covid-19 vaccine, moderna covid-19 vaccine) general pediatric inclusion criteria individuals 2-17 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, the international league of associations for rheumatology (ilar) classification for jia, the 2017 mcdonald 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 be assessed based on the disease that is selected for study entry. parents/guardians of all pediatric participants and participants ages 14 - 17 must be willing and able to sign informed consent. participants ages 7-13 must be willing and able to sign assent. 5. 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 bcdt cohort, participant must have received an anti-cd20 or an anti-cd19 bcdt in the past 18 months. 6. no changes in background is medications, including mmf/mpa or mtx, in the 8 weeks prior to screening, excluding the following: a. hcq, b. intraarticular steroids, c. the addition of prednisone at <0.15mg/kg/dose per day or prednisone at any dose when given for ≤3 days, and d. corticosteroid bursts for non-autoimmune disease-related conditions, such as asthma or copd, are permitted general pediatric exclusion criteria 1. 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. pediatric stage 1-specific inclusion criteria: 4. negative or suboptimal serologic response to initial eua-authorized or fda-approved covid-19 vaccine doses, defined as an elecsys® anti-sars-cov-2 s result ≤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 1 baseline/week 0 visit initial covid-19 vaccine regimen is defined as: i. pfizer-biontech covid-19 vaccine (2 through 4 years of age): 3 age-appropriate doses ii. pfizer-biontech covid-19 vaccine (5 through 17 years of age): 2 age-appropriate doses iii. moderna covid-19 vaccine (2 through 17 years of age): 2 age-appropriate doses. pediatric stage 1-specific

None

None

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 90 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 participants with history of arterial or venous thrombosis, and/or history of recurrent miscarriages associated with clotting antibodies (anticardiolipin antibodies, anti-beta-2 glycoprotein i antibodies, and positive lupus anticoagulant) participants with a history of heparin-induced thrombocytopenia (hit) or thrombotic thrombocytopenic purpura (ttp) 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 any increase in disease activity at screening that would necessitate a change in medications 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

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 90 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 participants with history of arterial or venous thrombosis, and/or history of recurrent miscarriages associated with clotting antibodies (anticardiolipin antibodies, anti-beta-2 glycoprotein i antibodies, and positive lupus anticoagulant) participants with a history of heparin-induced thrombocytopenia (hit) or thrombotic thrombocytopenic purpura (ttp) 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 any increase in disease activity at screening that would necessitate a change in medications 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

individuals who meet any of these criteria are not eligible for enrollment as study participants- 1. inability or unwillingness of a participant to give written informed consent or comply with study protocol 2. 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) 3. ongoing treatment for a malignancy with chemotherapy or immunotherapy 4. 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 5. 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 6. 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 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 8. 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 9. 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 10. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy 11. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 90 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. participants with history of arterial or venous thrombosis, and/or history of recurrent miscarriages associated with clotting antibodies (anticardiolipin antibodies, anti-beta-2 glycoprotein i antibodies, and positive lupus anticoagulant) 14. participants with a history of heparin-induced thrombocytopenia (hit) or thrombotic thrombocytopenic purpura (ttp) 15. currently pregnant or breastfeeding 16. participants who are planning a pregnancy during the course of the trial 17. hemoglobin (hgb) < 8.0 g/dl (80 g/l) 18. 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 19. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of enrollment 20. concurrent treatment with cyclophosphamide, cladribine, alemtuzumab, or mitoxantrone 21. any increase in disease activity at screening that would necessitate a change in medications 22. participants currently on any type of dialysis, or who have received a solid organ transplant 23. 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

individuals who meet any of these criteria are not eligible for enrollment as study participants- 1. inability or unwillingness of a participant to give written informed consent or comply with study protocol 2. 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) 3. ongoing treatment for a malignancy with chemotherapy or immunotherapy 4. 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 5. 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 6. 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 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 8. 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 9. 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 10. participants with common variable immunodeficiency disease, as well as any participants currently receiving immune globulin replacement therapy 11. participants who received licensed or investigational monoclonal antibodies or plasma products directed against sars-cov-2 within 90 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. participants with history of arterial or venous thrombosis, and/or history of recurrent miscarriages associated with clotting antibodies (anticardiolipin antibodies, anti-beta-2 glycoprotein i antibodies, and positive lupus anticoagulant) 14. participants with a history of heparin-induced thrombocytopenia (hit) or thrombotic thrombocytopenic purpura (ttp) 15. currently pregnant or breastfeeding 16. participants who are planning a pregnancy during the course of the trial 17. hemoglobin (hgb) < 8.0 g/dl (80 g/l) 18. 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 19. other investigational chemical agent within 30 days or other investigational biologic agent within 8 weeks or 5 half-lives (whichever is longer) of enrollment 20. concurrent treatment with cyclophosphamide, cladribine, alemtuzumab, or mitoxantrone 21. any increase in disease activity at screening that would necessitate a change in medications 22. participants currently on any type of dialysis, or who have received a solid organ transplant 23. 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