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BackgroundIt is critical to monitor changes in vaccine effectiveness against COVID-19 outcomes for various vaccine products in different population subgroups.MethodsWe conducted a retrospective study in patients ≥12 years who underwent testing for the SARS-CoV-2 virus from April 1 - October 25, 2021 at urgent care centers in the New York City metropolitan area. Patients self-reported vaccination status at the time of testing. We used a test-negative design to estimate vaccine effectiveness (VE) by comparing odds of a positive test for SARS-CoV-2 infection among vaccinated (n=484,468), partially vaccinated (n=107,573), and unvaccinated (n=466,452) patients, adjusted for demographic factors and calendar time.ResultsVE against symptomatic infection after 2 doses of mRNA vaccines was 96% (95% Confidence Interval [CI]: 95%, 97%) in the pre-delta period and reduced to 79% (95% CI: 77%, 81%) in the delta period. In the delta period, VE for 12–15-year-olds (85%; [95% CI: 81%, 89%]) was higher compared to older age groups (ConclusionsVE against infection after two doses of the mRNA vaccine was high initially, but significantly reduced against the delta variant for all three FDA-approved vaccines. |
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