This is a summary, written by members of the CITF Secretariat, of:

Kabbani D, Yotis DM, Ferreira VH, Shalhoub S, Belga S, Tyagi V, Ierullo M, Kulasingam V, Hébert MJ, West L, Delisle JS, Racine N, De Serres SA, Cardinal H, Dieudé M, Humar A, Kumar D. Immunogenicity, Safety, and Breakthrough Severe Acute Respiratory Syndrome Coronavirus 2 Infections After Coronavirus Disease 2019 Vaccination in Organ Transplant Recipients: A Prospective Multicenter Canadian Study. Open Forum Infect Dis. 2023 Apr 13;10(5):ofad200. doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, published in Open Forum Infectious Diseases, found that for solid organ transplant recipients (SOTRs), COVID-19 vaccines are safe, induce high levels of SARS-CoV-2 receptor binding domain (RBD) following a third dose (in most SOTRs), and offer protection from hospitalization. Recipients of solid organ transplants who experienced a breakthrough infection following three COVID-19 vaccine doses had increased levels of SARS-CoV-2 anti-RBD antibodies compared to those with three vaccine doses and no infection. This study was led by Dr. Deepali Kumar (University Health Network).

Key findings:

  • COVID-19 vaccines were found to be safe in SOTRs with low rates of rejection requiring therapy (0.7%).
  • After the third vaccine dose, immunogenicityThe ability to induce an antibody and/or cell-mediated immune response. improved in most recipients generating high anti-receptor binding domain (RBD) responses. However, 21% of participants did not develop a SARS-CoV-2 RBD response.
  • Recipients who were older, had a lung transplant or chronic kidney disease, or who had more recently received their transplant, were more likely to have low anti-RBD responses.
  • Recipients with at least three COVID-19 vaccine doses were protected from hospitalization when experiencing SARS-CoV-2 breakthrough infections. Those who were hospitalized had two or fewer doses of vaccine.
  • Recipients with three COVID-19 vaccine doses and a breakthrough infection had significantly higher levels of SARS-CoV-2 anti-RBD levels compared to those with three vaccine doses and no infection.

Although protective immune responses were found following COVID-19 vaccination in SOTRs, as they are for everyone, immunity wanes over time, requiring vaccine boosters for additional anti-RBD immunity. The authors also highlight the need for transplant recipients to continue practicing infection prevention measures, adding they should be prioritized for SARS-CoV-2 pre-exposure monoclonal antibodies and early therapeutics.

This was an observational study which included 539 solid organ transplant recipients aged 18 years and older recruited from seven Canadian transplant centers in April 2021 and observed until May 2022. The participants consisted of 48% kidney, 22.3% liver, 14.9% lung, 10.8% heart, and 3.9% multiorgan or other transplant recipients. Whole blood for anti-spike RBD testing was collected four to six weeks after each vaccination and each documented SARS-CoV-2 infection.