September 28, 2022
Vaccination Against SARS-CoV-2 Protects Solid Organ Transplant Recipients From COVID-19By A. Krishna Rao, MD, MS
Patients with immunocompromising conditions, including solid organ transplant recipients (SOTRs), have been at increased risk of contracting SARS-CoV-2 and developing severe COVID-19. While vaccination is an effective public health strategy in the general population, its efficacy in SOTRs has not been well established. In this study by Tucker et al. published in Transplant Infectious Disease, the investigators assessed the protection afforded by SARS-CoV-2 vaccination against subsequent COVID-19 and severity/mortality.
Notably, the study included subjects ≥ 18 years of age with no prior SARS-CoV-2 infection and observed them from Jan. 1, 2021, to Aug. 6, 2021, since before this time frame, vaccines were not widely available, and after this time frame, the CDC guidelines on vaccination of immunocompromised individuals recommended a third dose. Because the investigators conducted a retrospective cohort study and subjects were not randomized to receive the vaccine, many potentially confounding factors could have influenced the vaccination status of subjects. To address this, they generated a propensity score for vaccination status using age, sex, race/ethnicity, comorbidities, mycophenolate use, type of transplanted organ, and years after transplant, from a starting cohort of 1,427 fully vaccinated (≥ 14 days from one dose of the Ad26.COV2.S vaccine or second dose of the mRNA-1273 or BNT162b2 vaccines as of Aug. 6, 2021) and 934 not fully vaccinated subjects (total N = 2,631). The propensity score was used to create a tightly matched cohort (matched subjects with scores of difference ≤ 1%) of 834 vaccinated/not-vaccinated subjects (total N = 1,668).
The final matched cohort was balanced across all covariates, and a Cox regression model found that fully vaccinated subjects had a 73% (94% confidence interval [CI], 42%-87%) reduction in the SARS-CoV-2 infection rate and a 76% (95% CI, 5%-94%) reduction in all-cause mortality. In addition to the usual concerns with retrospective studies over data reliability/availability and unmeasured confounders, there are additional limitations to the study including that many subjects could not be matched and were excluded, and that infection risk varies over time and space, but such variables were not included/modeled in the analyses. However, this was a large study that demonstrated a robust protective effect of vaccination against both SARS-CoV-2 infection and all-cause mortality.
Thus, this study provides strong evidence in favor of a protective effect of vaccines against SARS-CoV-2 even in SOTRs. However, its time frame of 2021 and the continued evolution of the virus and the pandemic warrant additional, contemporaneous studies revisiting this question to provide SOTRs and their clinical teams updated guidance on vaccine efficacy in this important population of patients.
