Abstract
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.
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