Subproject: Fixed Price

This is a randomized, open-label multi-site trial designed to induce an enhanced antibody response to SARS-CoV-2 in kidney and liver transplant recipients who have negative or indeterminate (<0.8 U/mL) anti-spike antibody after at least two mRNA COVID-19 vaccines. Participants will be randomized to two 2 groups: Group One will undergo a temporary, prescribed reduction in their maintenance immunosuppressive regimen (ISR) and receive an additional dose of mRNA-based COVID-19 vaccine while Group Two will receive an additional dose of mRNA-based COVID-19 vaccine with no change in their maintenance immunosuppressive regimen. The primary endpoint is the proportion of participants who achieve an antibody response >50 U/mL (using the Roche Elecsysâ anti-SARS-CoV-2 S assay) at 30 days after the study dose of vaccine. Liver and kidney transplant recipients who received transplants at least one year prior, have no evidence of allograft rejection in the last 6 months, no anti-donor HLA antibodies at screening, who have received a minimum of 2 doses of either the Moderna COVID-19 vaccine or Pfizer-BioNTech COVID-19 vaccine at least 30 days prior, with serum antibody negative or indeterminate (titer <0.8 U/mL) as measured by the Roche Elecsys® anti-SARS-CoV-2 S assay at >30 days from the last dose of mRNA COVID-19 vaccine, and are currently taking an approved tacrolimus based regimen will be eligible. Eligible subjects will be enrolled, randomized to the intervention and followed for 13 months. This study will utilize a central IRB. Sites will maintain updated subject logs and completed consent forms and other necessary regulatory documents including updated delegation of authority logs, current medical licenses, and human subject training certificates. The site principal investigator will remain responsible for the safe and effective conduct of the study at the site. In sum, sites are responsible for cooperating with the Coordinating Center to ensure the successful implementation and administration of the study. Sites will be responsible for: 1) Identifying and screening potential participants using clinical criteria 2) Consent and send eligible participants for antibody testing with the Roche Elecsys® anti-SARSCoV- 2 S assay 3) Review antibody results and if eligible, consent and enroll participants in the RCT phase 4) Randomize participants and implement immunosuppression reduction as indicated for Group One 5) Vaccinate individuals in both groups with an additional dose of mRNA-based COVID-19 vaccine 6) Register the participant in the REDCap database and complete case report forms 7) Collect research samples and clinical results listed in the protocol; 8) Actively follow the participant, completing follow-up visits according to the protocol; 9) Promptly report serious adverse events using the reporting forms 10) The principal investigator of the study will be responsible for determining the clinical assessments detailed in the protocol; 11) Study materials will be archived for at least three years after completion of subject participation. Data will be collected in online case report forms using the REDCap System for the following endpoints:  Primary endpoint: antibody response using the Roche Elecsys anti-SARS-CoV-2 S assay at 30 days  Local and systemic vaccine reactogenicity and/or allergy  Serious adverse events occurring during the 30 days following the additional dose of vaccine  Incidence of treated acute cell-mediated and/or antibody-mediated allograft rejection (clinical or biopsy-proven) w