ABSTRACT
BackgroundBelief in immunity from prior infection and concern that vaccines might not protect against new variants are contributors to vaccine hesitancy. We assessed effectiveness of full and partial COVID-19 vaccination against reinfection when Delta was the predominant variant in New York City. MethodsWe conducted a case-control study in which case-patients with reinfection during June 15- August 31, 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. Conditional logistic regression was used to calculate matched odds ratios (mOR) and 95% confidence intervals (CI). ResultsOf 349,598 adult residents who tested positive for SARS-CoV-2 infection in 2020, did not test positive again >90 days after initial positive test through June 15, 2021, and did not die before June 15, 2021, 1,067 were reinfected during June 15-August 31, 2021. Of 1,048 with complete matching criteria data, 499 (47.6%) were known to be symptomatic for COVID-19-like-illness, and 75 (7.2%) were hospitalized. Unvaccinated individuals, compared with fully vaccinated individuals, had elevated odds of reinfection (mOR, 2.23; 95% CI, 1.90, 2.61), of symptomatic reinfection (mOR, 2.17; 95% CI, 1.72, 2.74), and of reinfection with hospitalization (mOR, 2.59; 95% CI, 1.43, 4.69). Partially versus fully vaccinated individuals had 1.58 (95% CI: 1.22, 2.06) times the odds of reinfection. All three vaccines authorized or approved for use in the U.S. were similarly effective. ConclusionAmong adults with previous SARS-CoV-2 infection, vaccination reduced odds of reinfections when the Delta variant predominated.
