Reduced Odds of SARS-CoV-2 Reinfection after Vaccination among New York City Adults, July-November 2021.

BACKGROUND: Belief that vaccination is not needed for individuals with prior infection contributes to COVID-19 vaccine hesitancy. Among individuals infected with SARS-CoV-2 before vaccines became available, we assessed whether vaccinated individuals had reduced odds of reinfection. METHODS: We conducted a case-control study among adult New York City residents who tested positive for SARS-CoV-2 infection in 2020, did not test positive again >90 days after initial positive test through July 1, 2021, and did not die before July 1, 2021. Case-patients with reinfection during July-November 2021 and control subjects with no reinfection were matched (1:3) on age, sex, timing of initial positive test in 2020, and neighborhood poverty level. Matched odds ratios (mOR) and 95% confidence intervals (CI) were calculated using conditional logistic regression. RESULTS: Of 349,827 eligible adults, 2,583 were reinfected during July-November 2021. Of 2,401 with complete matching criteria data, 1,102 (45.9%) were known to be symptomatic for COVID-19-like-illness, and 96 (4.0%) were hospitalized. Unvaccinated individuals, compared with individuals fully vaccinated within the prior 90 days, had elevated odds of reinfection (mOR, 3.21; 95% CI, 2.70, 3.82), of symptomatic reinfection (mOR, 2.97; 95% CI, 2.31, 3.83), and of reinfection with hospitalization (mOR, 2.09; 95% CI, 0.91, 4.79). All three vaccines authorized or approved for use in the U.S. were similarly effective. CONCLUSION: Vaccination reduced odds of reinfections when the Delta variant predominated. Further studies should assess risk of severe outcomes among reinfected persons as new variants emerge, infection- and vaccine-induced immunity wanes, and booster doses are administered.