Hybrid immunity protection against SARS-CoV-2 and severe COVID-19 in kidney transplantation: a retrospective, comparative cohort study

Hybrid immunity, resulting from a combination of SARS-CoV-2 infection and vaccination, offers robust protection against COVID-19 in the general population. However, its impact on immunocompromised patients remains unexplored. We investigated the effect of hybrid immunity against the Omicron variant in a population of kidney transplant recipients receiving the fourth dose mRNA monovalent vaccination. By extracting data from the clinical records and performing individual interviews, participants were categorised into the hybrid cohort (previously infected and vaccinated individuals) and the vaccine cohort (vaccinated-only individuals). The study comprised 1,114 participants, 442 in the hybrid and 672 in the vaccine cohorts. From April 2022 to August 2023, 286 infections, 38 hospitalisations and 9 deaths were reported. The cumulative incidence of infection was 12.1% (95% CI 9.03-16.03) for the hybrid cohort and 36.54% (95% CI 32.81-40.54) for the vaccine cohort after 300 days of follow-up. Hybrid immunity was associated to a 72% lower risk of infection (adjusted hazard ratio [aHR] 0.28 [95% CI 0.21-0.38]) and a 96% lower risk of hospitalisation (aHR 0.04 [95% CI 0.01-0.32]). No deaths occurred in the hybrid cohort. Hybrid immunity was associated with a lower incidence of SARS-CoV-2 infection and severe COVID-19, underscoring its importance for risk stratification in this vulnerable patient population.