Effectiveness of Covid-19 vaccines against symptomatic and asymptomatic SARS-CoV-2 infections in an urgent care setting
Abstract
Background
It is critical to monitor changes in vaccine effectiveness against COVID-19 outcomes for various vaccine products in different population subgroups.
Methods
We 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.
Results
VE 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 (<65% for all other age groups). VE estimates did not differ by sex, race/ethnicity, and comorbidity. VE against symptomatic infection was the highest for individuals with a prior infection followed by full vaccination. VE against symptomatic infection after the mRNA-1273 vaccine (83% [95% CI: 81%, 84%]) was higher compared to the BNT162b2 vaccine (76% [95% CI: 74%, 78%]) in the delta period. VE after the single-dose Ad26.COV2.S vaccine was the lowest compared to other vaccines (29% [95% CI: 26%, 32%]) in the delta period.
Conclusions
VE 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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