inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- 1. able to understand and provide informed consent 2. individual ≥18 years of age. 3. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment 4. negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). 5. currently taking one of the following tacrolimus-based immunosuppressive regimens: * tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid * tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent 6. received a minimum of 3 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine 7. participant must be ≥ 60 days after completion of primary vaccination or receipt of the most recent booster dose with any authorized or approved monovalent or bivalent covid-19 vaccine at the time of study vaccine. 8. serum antibody negative or low (titer ≤ 2500 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine and ≥ 30 days following receipt of a monoclonal antibody product or convalescent plasma for covid-19, measured using the roche elecsys® anti-sars-cov-2 s assay. 9. participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- 1. able to understand and provide informed consent 2. individual ≥18 years of age. 3. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment 4. negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). 5. currently taking one of the following tacrolimus-based immunosuppressive regimens: * tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid * tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent 6. received a minimum of 3 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine 7. participant must be ≥ 60 days after completion of primary vaccination or receipt of the most recent booster dose with any authorized or approved monovalent or bivalent covid-19 vaccine at the time of study vaccine. 8. serum antibody negative or low (titer ≤ 2500 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine and ≥ 30 days following receipt of a monoclonal antibody product or convalescent plasma for covid-19, measured using the roche elecsys® anti-sars-cov-2 s assay. 9. participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent individual ≥18 years of age. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following tacrolimus-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 3 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine participant must be ≥ 60 days after completion of primary vaccination or receipt of the most recent booster dose with any authorized or approved monovalent or bivalent covid-19 vaccine at the time of study vaccine. serum antibody negative or low (titer ≤ 2500 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine and ≥ 30 days following receipt of a monoclonal antibody product or convalescent plasma for covid-19, measured using the roche elecsys® anti-sars-cov-2 s assay. participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent individual ≥18 years of age. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following tacrolimus-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 3 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine participant must be ≥ 60 days after completion of primary vaccination or receipt of the most recent booster dose with any authorized or approved monovalent or bivalent covid-19 vaccine at the time of study vaccine. serum antibody negative or low (titer ≤ 2500 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine and ≥ 30 days following receipt of a monoclonal antibody product or convalescent plasma for covid-19, measured using the roche elecsys® anti-sars-cov-2 s assay. participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent individual ≥18 years of age. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following tacrolimus-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 3 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine participant must be ≥ 60 days after completion of primary vaccination or receipt of the most recent booster dose with any authorized or approved monovalent covid-19 vaccine at the time of study vaccine. serum antibody negative or low (titer ≤ 2500 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine and ≥ 30 days following receipt of a monoclonal antibody product or convalescent plasma for covid-19, measured using the roche elecsys® anti-sars-cov-2 s assay. participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent individual ≥18 years of age. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following tacrolimus-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 3 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine participant must be ≥ 60 days after completion of primary vaccination or receipt of the most recent booster dose with any authorized or approved monovalent covid-19 vaccine at the time of study vaccine. serum antibody negative or low (titer ≤ 2500 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine and ≥ 30 days following receipt of a monoclonal antibody product or convalescent plasma for covid-19, measured using the roche elecsys® anti-sars-cov-2 s assay. participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 2 and no more than 4 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine at least 30 days prior to study entry serum antibody negative or low (titer ≤ 250 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 2 and no more than 4 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine at least 30 days prior to study entry serum antibody negative or low (titer ≤ 250 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 2 and no more than 4 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine at least 30 days prior to study entry serum antibody negative or indeterminate (titer <0.8 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 2 and no more than 4 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine at least 30 days prior to study entry serum antibody negative or indeterminate (titer <0.8 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and participant's transplant physician or midlevel practitioner who is clinically licensed to prescribe and manage immunosuppression must confirm the participant's eligibility based on medical history.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 2 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine at least 30 days prior to study entry serum antibody negative or indeterminate (titer <0.8 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and participant's transplant physician must confirm the participant's eligibility based on medical history and concur with the plan for immunosuppression modification.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- able to understand and provide informed consent recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent received a minimum of 2 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine at least 30 days prior to study entry serum antibody negative or indeterminate (titer <0.8 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and participant's transplant physician must confirm the participant's eligibility based on medical history and concur with the plan for immunosuppression modification.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- 1. able to understand and provide informed consent 2. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment 3. negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). 4. currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: - tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid - tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent 5. received a minimum of 2 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine at least 30 days prior to study entry 6. serum antibody negative or indeterminate (titer <0.8 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and 7. participant's transplant physician must confirm the participant's eligibility based on medical history and concur with the plan for immunosuppression modification.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- 1. able to understand and provide informed consent 2. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment 3. negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). 4. currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: - tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid - tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent 5. received a minimum of 2 doses of either the moderna coronavirus infectious disease 19 (covid-19) vaccine or pfizer-biontech covid-19 vaccine at least 30 days prior to study entry 6. serum antibody negative or indeterminate (titer <0.8 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and 7. participant's transplant physician must confirm the participant's eligibility based on medical history and concur with the plan for immunosuppression modification.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- 1. able to understand and provide informed consent 2. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment 3. negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). 4. currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: - tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid - tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent 5. received a minimum of 2 doses of either the moderna coronavirus infectious disease 19 (covid-19)covid-19 vaccine or pfizer- biontech covid-19 vaccine at least 30 days prior to study entry 6. serum antibody negative or indeterminate (titer <0.8 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and 7. participant's transplant physician must confirm the participant's eligibility based on medical history and concur with the plan for immunosuppression modification.

inclusion criteria: individuals who meet all the following criteria are eligible for enrollment as study participants- 1. able to understand and provide informed consent 2. recipient of a kidney or liver transplant ≥12 months prior to enrollment, without allograft rejection in the 6 months preceding enrollment 3. negative for anti-donor human leukocyte antigens (hla) antibodies at screening (central lab test determination). 4. currently taking one of the following calcineurin inhibitors (cni)-based immunosuppressive regimens: - tacrolimus plus mycophenolate mofetil (mmf) or mycophenolic acid (mpa), with or without a corticosteroid - tacrolimus with trough ≥ 5ng/ml with or without ≤5 mg of prednisone or equivalent 5. received a minimum of 2 doses of either the moderna coronavirus infectious disease 19 (covid-19)covid-19 vaccine or pfizer- biontech covid-19 vaccine at least 30 days prior to study entry 6. serum antibody negative or indeterminate (titer <0.8 u/ml) at ≥ 30 days from the last dose of mrna covid-19 vaccine, measured using the roche elecsys®) severe acute respiratory syndrome coronavirus type 2 serological (anti-sars-cov-2) s assay, and 7. participant's transplant physician must confirm the participant's eligibility based on medical history and concur with the plan for immunosuppression modification.