Evaluating Clinical Effectiveness of SARS-CoV-2 Vaccine in Solid Organ Transplant Recipients: A Propensity Score Matched Analysis

Background: Solid organ transplant recipients (SOTRs) are at disproportionate risk for severe Coronavirus Disease 2019 (COVID-19). Vaccination is a key preventative strategy but is associated with decreased humoral responses among SOTR. Whether dampened immune responses correlate with reduced clinical effectiveness is unclear. Our study was designed to evaluate the clinical effectiveness of SARS-CoV-2 vaccination in the early vaccine era.

Methods: We conducted a retrospective cohort study comparing SARS-CoV-2 infection rates between SOTRs who received two doses of mRNA or one dose of Ad26.Cov2.S vaccine and those not fully vaccinated (partially vaccinated and unvaccinated). To evaluate clinical effectiveness of vaccine, cause-specific Cox regression model and modified Poisson regression model were built using the propensity score-matched cohort. Additionally, the clinical outcomes of COVID-19 of fully vaccinated and not fully vaccinated SOTR were compared.

Results: Of 2705 SOTRs, 1668 were included in our final matched analysis, which showed a 73% reduction of SARS-CoV-2 infection and 76% reduction of all-cause-mortality among fully vaccinated patients. Thirty-nine SOTRs developed SARS-CoV-2 infection, including nine fully vaccinated and 30 not fully vaccinated. Among fully vaccinated patients, 22% had severe/critical COVID-19 and 0% mortality versus not fully vaccinated SOTRs, of whom 37% had severe/critical COVID-19 and 6.67% COVID-19-related mortality.

Conclusion: In SOTRs, completion of primary vaccine series in the early vaccine era was associated with a significant reduction of COVID-19 and was protective against severe/critical disease and death. Further studies are needed to evaluate the clinical effectiveness of current vaccine recommendations for SOTR against emerging new variants.