Effectiveness of the BNT162b2 Vaccine after Recovery from Covid-19

Abstract

Background: The risk of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) decreases substantially among patients who have recovered from coronavirus disease 2019 (Covid-19). However, it is unknown how long protective immunity lasts. Current guidelines recommend vaccination of recovered patients even though data regarding vaccine effectiveness in such cases are still limited.

Methods: In this retrospective cohort study, we reviewed electronic medical records from a large health care organization in Israel to assess reinfection rates in patients who had recovered from SARS-CoV-2 infection before any vaccination against Covid-19. We compared reinfection rates among patients who had subsequently received the BNT162b2 vaccine (Pfizer-BioNTech) and those who had not been vaccinated between March 1 and November 26, 2021. We used a Cox proportional-hazards regression model with time-dependent covariates to estimate the association between vaccination and reinfection after adjustment for demographic factors and coexisting illnesses. Vaccine effectiveness was estimated as 1 minus the hazard ratio. In a secondary analysis, we evaluated the vaccine effectiveness of one dose as compared with two doses.

Results: A total of 149,032 patients who had recovered from SARS-CoV-2 infection met the eligibility criteria. Of these patients, 83,356 (56%) received subsequent vaccination during the 270-day study period. Reinfection occurred in 354 of the vaccinated patients (2.46 cases per 100,000 persons per day) and in 2168 of 65,676 unvaccinated patients (10.21 cases per 100,000 persons per day). Vaccine effectiveness was estimated at 82% (95% confidence interval [CI], 80 to 84) among patients who were 16 to 64 years of age and 60% (95% CI, 36 to 76) among those 65 years of age or older. No significant difference in vaccine effectiveness was found for one dose as compared with two doses.

Conclusions: Among patients who had recovered from Covid-19, the receipt of at least one dose of the BNT162b2 vaccine was associated with a significantly lower risk of recurrent infection.

Figure 1. Assessment for Eligibility.

The study included members of the Israeli Clalit Health Services who had recovered from documented coronavirus disease 2019 (Covid-19) at least 100 days earlier and who had not received any vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the time of infection. Eligible patients had a primary infection that occurred between August 23, 2020 (190 days before study initiation), and May 31, 2021 (90 days after study initiation).

Figure 2. Cumulative Risk of Reinfection with SARS-CoV-2, According to Age and Subsequent Vaccination Status.

Shown is the cumulative risk of reinfection with SARS-CoV-2 among previously unvaccinated patients who had recovered from Covid-19 and who were between 16 and 64 years of age (Panel A) or were 65 years of age or older (Panel B). Shading indicates the 95% confidence interval, and hatch marks indicate data censoring.