Protection and Waning of Natural and Hybrid Immunity to SARS-CoV-2
A lthough a decline in protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection after two doses of BNT162b2 vaccine (Pfizer–BioNTech) has been observed in several studies, the level of protection remains unclear, as does the presence or extent of waning of natural immunity. Several studies have shown that 6 or more months after infection, persons still have substantial natural immunity against SARS-CoV However, one recent study showed that messenger RNA (mRNA)–based vaccines confer a level of protection against
hospitalization that is five times as high as that provided by previous infection.
In this study, authors estimated the incidence of confirmed SARS-CoV-2 infection in the following cohorts: previously infected, unvaccinated persons; previously infected persons who had also received the BNT162b2 vaccine; and vaccinated persons who had not been previously infected. For each cohort, we quantified the association between the time that had passed since infection or vaccination and the rate of confirmed infection. By comparing the rates of infection among these groups, we were able to assess the level of protection afforded by hybrid immunity as compared with that afforded by natural immunity or immunity conferred by vaccination.
