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 to 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 to 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 mRNA1273 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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“…While vaccine effectiveness against different variants is still being evaluated, initial evidence suggested a decrease in protection against symptomatic infection after 6 months following vaccination [ 7 , 8 ]. In comparison, protection against severe disease and hospitalization remained relatively high against the Delta variant but may wane against the Omicron variant [ 9 – 14 ]. Together, the shifting dynamics created by ongoing vaccination, increased background immunity due to the surge of infections associated with the Delta variant, shifting characteristics of emerging viral variants and changes in social distancing and masking practices have created uncertainty around the future trajectory of epidemic in the U.S. and elsewhere.…”