Impact on the time elapsed since SARS-CoV-2 infection, vaccination history, and number of doses, on protection against reinfection

Abstract

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 number of doses received. We conducted a retrospective study in 746 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. Also, an adjusted Cox-regression was performed to evaluate the risk of reinfection in all groups. The t_RI was significantly higher in those vaccinated vs. non-vaccinated (p < 0.001). However, an early incomplete regime 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 (adj-p < 0.001). Actually, early vaccination with complete and booster regimes provided lower length of protection compared to vaccinating later with incomplete and complete regime, respectively. Vaccination with complete and booster regimes significantly increases the t_RI (adj-p < 0.001). 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 and reduces the risk of reinfection, especially in complete and booster regimes. Those results emphasize the role of vaccines and boosters during the pandemic and can guide strategies on future vaccination policy.

Figure 1

Diagram of selection criteria for individuals in the study.

Figure 2

Diagram of the different time parameters analyzed in the study of reinfection.

Figure 3

Time of reinfection (t_RI). The time elapsed between first and second COVID-19 infection and the comparison between vaccinated (with either incomplete, complete or booster regime) and non-vaccinated is represented. The two-tailed p-value was calculated by applying Mann–Whitney U-test; ***p < 0.001.

Figure 4

(a) The Cumulative Incidence of time between both Covid-19 infections (t_RI) of different cohorts was represented as 1 minus the Kaplan–Meier estimator. Difference between cumulative incidence was assessed by log-rank test. (b) The Cumulative Incidence of time between last dose and reinfection (t₂) of different cohorts was represented as 1 minus the Kaplan–Meier estimator. Difference between cumulative incidence was assessed by log-rank test.