Association of COVID-19 Vaccination With Symptomatic SARS-CoV-2 Infection by Time Since Vaccination and Delta Variant Predominance

Abstract

Among adults, the OR for the association between symptomatic SARS-CoV-2 infection and COVID-19 vaccination (as an estimate of vaccine effectiveness) was higher during Delta variant predominance, suggesting lower protection. For mRNA vaccination, the steady increase in OR by month since vaccination was consistent with attenuation of estimated effectiveness over time; attenuation related to time was greater than that related to variant.