Hybrid Immunization In COVID-19: Time Matters

Purpose: SARS-CoV-2 reinfections have been frequent, even among those vaccinated. The aim of this study is to know if hybrid immunity (infection+vaccination) is affected by the moment of vaccination and the number of doses received. Methods: We conducted a retrospective study in 745 patients with a history of COVID-19 reinfection and recovered the dates of infection and reinfection and vaccination status (date and number of doses). To assess differences in the time to reinfection(t RI ) between unvaccinated, vaccinated before 6 months and later, and comparing one, two or three doses(incomplete, complete and booster regime) we performed the log-rank test of the cumulative incidence calculated as 1 minus the Kaplan-Meier estimator. Results: The t RI was significantly higher in those vaccinated vs. non-vaccinated (q<0.001). However, an early incomplete regime(1 dose) protects similar time than not receiving a vaccine. Vaccination before 6 months after infection showed a lower t RI compared to those vaccinated later with the same regime(q<0.001). Actually, early vaccination with complete(2 doses) and booster regimes(3 doses) provided lower length of protection compared to vaccinating later with incomplete(1 dose) and complete regime(2 doses), respectively. Vaccination with complete and booster regimes significantly increases the t RI (q<0.001). Conclusion: Vaccination increases the time it takes for a person to become reinfected with SARS-CoV-2. Increasing the time from infection to vaccination increases the time in which a person could be reinfected. Booster doses increase the time to reinfection. Those results emphasize the role of vaccines and boosters during the pandemic and can guide strategies on future vaccination policy.