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 kidney transplant ≥12 months prior to enrollment, without treated allograft rejection in the 6 months preceding enrollment; Received 2 doses of either the Moderna COVID-19 vaccine or Pfizer-BioNTech COVID-19 vaccine as specified in the respective Food and Drug Administration Emergency Use Authorization (FDA EUAs), >30 days and <8 months prior to enrollment ; and, Negative (antibody titer < 0.8U/mL) or low (antibodies detected at titer ≤ 50 U/mL) response to the vaccine at > 30 days from dose 2 of the Moderna COVID-19 vaccine or the Pfizer BioNTech vaccine, using the Roche Elecsys® anti-Receptor Binding Domain (RBD) assay.  Exclusion Criteria:  Individuals who meet any of these criteria are not eligible for enrollment as study participants-  Recipient of any number of doses of any COVID vaccine product other than the Moderna COVID-19 vaccine or the Pfizer-BioNTech COVID-19 vaccine; Known history of severe allergic reaction to any component of either the Moderna COVID-19 vaccine or Pfizer-BioNTech COVID-19 vaccine; Thrombotic events, myocarditis, or pericarditis temporally associated with prior dose of COVID-19 vaccine; Any change in transplant immunosuppression regimen (drug or dose) in response to suspected or proven rejection within the last 6 months; Significant graft dysfunction; Receipt of any cellular depleting agent (e.g. ATG, Rituximab, Alemtuzumab, Cyclophosphamide) within 12 months preceding enrollment; Receiving systemic immunomodulatory medication(s) for any condition other than transplant; Any untreated active infection, including BK viremia >10^4 copies; Infection with human immunodeficiency virus (HIV); Maintenance immunosuppressive regimen that includes belatacept or abatacept; Recent (within one year) or ongoing treatment for malignancy; or Any past or current medical problems, treatments, or findings which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the candidate's ability to comply with study requirements or may impact the quality or interpretation of the data obtained from the study.