for people ages 18 years and up (full criteria)
at San Francisco, California and other locations
study started
estimated completion
Principal Investigator
by Monica Fung, MD
Headshot of Monica Fung
Monica Fung



This study will enroll individuals who have:

  • Completed a primary series of either the Moderna messenger RNA (mRNA) based coronavirus infectious disease 19 (COVID-19) vaccine or the Pfizer-BioNTech mRNA based COVID-19 vaccine, and
  • An antibody response ≤ 2500 U/mL measured at least 30 days after the last dose of vaccine.

This group of patients is at high risk for severe COVID-19 disease due to pharmacologic immunosuppression and a high prevalence of non-transplant risk factors such as obesity and diabetes.

Official Title

A Randomized Study to Evaluate Antibody Response to an Additional Dose of SARS-CoV-2 Vaccination With and Without Immunosuppression Reduction in Kidney and Liver Transplant Recipients


This study is a randomized, open-label multi-site trial designed to induce an enhanced antibody response to severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) in kidney and liver transplant recipients who have ≤ 2500 U/mL anti-spike antibody (as measured by the Roche Elecsys® anti-SARS-CoV-2 S assay) after a completed primary series (3 doses) of mRNA COVID-19 vaccines.

Participants will be randomized to either:

  1. Receive a study dose of mRNA based COVID-19 vaccine (booster) with no change in their immunosuppressive regimen, or
  2. Undergo a temporary, prescribed reduction in their maintenance immunosuppression (IS) regimen and receive a study dose (booster) of mRNA-based COVID-19 vaccine.

Protocol Version 6.0 will include a booster dose of either Pfizer Bivalent COVID-19 Vaccine or Moderna Bivalent COVID-19 Vaccine, with or without IS reduction.

Duration of study participation for interested and eligible individuals: 13 months.


Kidney Transplant Recipients, Liver Transplant Recipients, mRNA COVID-19 vaccines, SARS-CoV-2 antibody response, immunosuppression (IS), coronavirus infectious disease 19, COVID-19, severe acute respiratory syndrome coronavirus type 2, SARS-CoV-2 protection, Mycophenolic Acid, Vaccines, Tacrolimus, Pfizer-BioNTech Bivalent COVID-19 Vaccine, Moderna Bivalent COVID-19 Vaccine, SOC IS Regimen, SOC IS Reduction


You can join if…

Open to people ages 18 years and up

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 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.

You CAN'T join if...

Individuals who meet any of these criteria are not eligible for enrollment as study participants-

  1. Currently on an immunosuppressive regimen different from the three regimens described in the Inclusion Criteria, for example (but not limited to) those including sirolimus, everolimus, belatacept, or azathioprine
  2. Recipient of any allograft other than a kidney or liver
  3. Participant is pregnant
  4. Any past history of Donor Specific Antibody (DSA) using local site standards
  5. Prior receipt of the Moderna Bivalent COVID-19 Vaccine or Pfizer-BioNTech Bivalent COVID-19 Vaccine.
  6. Currently taking any systemic immunosuppressive agent, other than their prescribed transplant immunosuppression
  7. Known history of severe allergic reaction to any component of an authorized or licensed COVID-19 vaccine
  8. Thrombotic events, myocarditis, or pericarditis temporally associated with a prior dose of COVID-19 vaccine
  9. History of heparin-induced thrombocytopenia
  10. Any change in transplant immunosuppression regimen (drug or dose) in response to suspected or proven rejection within the last 6 months
  11. More than minimal graft dysfunction, in accordance with study definition
  12. Receipt of any cellular depleting agent (e.g. antithymocyte globulins (ATG), rituximab, alemtuzumab, Cyclophosphamide) within 12 months preceding enrollment
  13. Concurrent autoimmune disease at risk for exacerbation with immunosuppression reduction
  14. Any untreated active infection including BK viremia >104 copies
  15. Infection with human immunodeficiency virus (HIV)
  16. Recent (within one year) or ongoing treatment for malignancy with the exception of:
  17. Treatment or prophylaxis of COVID-19 with a monoclonal antibody product or convalescent plasma within 6 months preceding enrollment, or
  18. 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,
    • interfere with the candidate's ability to comply with study requirements, or
    • impact the quality or interpretation of the data obtained from the study.


  • UCSF Health accepting new patients
    San Francisco California 94143 United States
  • University of California, San Diego accepting new patients
    San Diego California 92093 United States

Lead Scientist at UCSF

  • Monica Fung, MD
    Monica Fung specializes in infectious diseases with a focus on patients with compromised immune systems, including those with solid organ or stem cell transplants. She attends on the Immunocompromised and General Infectious Diseases Consult Services, and has clinics in the 360 Wellness Center and Infectious Diseases Faculty Practice at UCSF-Parnassus.


accepting new patients
Start Date
Completion Date
National Institute of Allergy and Infectious Diseases (NIAID)
National Institute of Allergy and Infectious Diseases Division of Allergy, Immunology, and Transplantation
Phase 2 research study
Study Type
Expecting 400 study participants
Last Updated