1. In a retrospective cohort study of individuals who recovered from SARS-CoV-2, BNT162b2 vaccination decreased the risk of recurrent infection.

Evidence Rating Level: 2 (Good)

Study Rundown: The long-term effectiveness and durability of immune protection provided after SARS-CoV-2 (Covid-19) infection are unclear. The purpose of this retrospective cohort study was to evaluate whether vaccination by the BNT162b2 Covid-19 (Pfizer-BioNTech) vaccine would protect against reinfection in individuals previously infected with Covid-19. In this retrospective cohort study, the electronic medical records of patients who had previously recovered from Covid-19 in Israel were reviewed for incidence of reinfection. Reinfection rates between individuals vaccinated with the BNT162b2 vaccine and unvaccinated individuals were compared to determine vaccine effectiveness. The study found that reinfection occurred in 2.46 cases per 100,000 persons per day in vaccinated individuals which were significantly lower compared to 10.21 cases per 100,000 persons per day amongst unvaccinated individuals, resulting in 82% vaccine effectiveness. Rates were similar between individuals vaccinated with one dose compared to those receiving two doses. Taken together, this study supports that previously infected individuals who also receive subsequent vaccination against Covid-19 are at lower risk for reinfection compared to those who are unvaccinated. The findings of this study are limited by the retrospective design of the study, reliance on irregular PCR testing, and analysis only of patients receiving the BNT162b2 vaccine.

Click to read the study in NEJM 

Relevant Reading: mRNA vaccination boosts cross-variant neutralizing antibodies elicited by SARS-CoV-2 infection

In-Depth [retrospective cohort]: In this retrospective cohort study, 149,032 electronic medical records of individuals previously infected with SARS-CoV-2 (Covid-19) in a single healthcare center in Israel were reviewed. Patients were eligible if they had recovered from documented Covid-19 infection 100 days before receipt of any vaccination and did not already experience Covid-19 reinfection. The study cohort was divided into those receiving at least one dose of BNT162b2 Covid-19 vaccine and unvaccinated with the primary outcome being the incidence of Covid-19 reinfection as determined by polymerase chain reaction (PCR) testing. The Cox proportional-hazards regression model was used to analyze statistical differences between the two groups. Reinfections were significantly lower in the vaccinated group where 354 of 83,356 individuals were reinfected (2.46 cases per 100,000 persons per day), compared to the unvaccinated group where 2,120 of 60,877 patients experienced reinfection (10.79 cases per 100,000 persons per day). The adjusted hazard ratio for protection against reinfection by vaccination was 0.18 (95% Confidence Interval [CI], 0.16-0.20) in patients between 16- 64 years old, and 0.40 (95% CI, 0.24-0.64) for those over 65. The vaccine effectiveness was estimated to be 82% (95% CI, 80-84). Reinfection rates were similar among individuals with a hazard ratio of 0.98 (95% CI, 0.64-1.5) for individuals receiving two doses compared to one dose. Overall, the study supports that vaccination with the BNT162b2 vaccine confers significant protection against Covid-19 reinfection in those already previously infected with Covid-19.

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