| Summary: | <h4>Background</h4>The CDC recently defined being "up-to-date" on COVID-19 vaccination as having received at least one dose of a COVID-19 bivalent vaccine. The purpose of this study was to compare the risk of COVID-19 among those "up-to-date" and "not up-to-date".<h4>Methods</h4>Employees of Cleveland Clinic in Ohio, USA, in employment when the COVID-19 bivalent vaccine first became available, and still employed when the XBB lineages became dominant, were included. Cumulative incidence of COVID-19 since the XBB lineages became dominant was compared across the"up-to-date" and "not up-to-date" states, by treating COVID-19 bivalent vaccination as a time-dependent covariate whose value changed on receipt of the vaccine. Risk of COVID-19 by vaccination status was also evaluated using multivariable Cox proportional hazards regression adjusting for propensity to get tested for COVID-19, age, sex, most recent prior SARS-CoV-2 infection, and number of prior vaccine doses.<h4>Results</h4>COVID-19 occurred in 1475 (3%) of 48 344 employees during the 100-day study period. The cumulative incidence of COVID-19 was lower in the "not up-to-date" than the "up-to-date" state. On multivariable analysis, being "up-to-date" was not associated with lower risk of COVID-19 (HR, 1.05; 95% C.I., 0.88-1.25; P-value, 0.58). Results were very similar when those 65 years and older were only considered "up-to-date" after 2 doses of the bivalent vaccine.<h4>Conclusions</h4>Since the XBB lineages became dominant, adults "up-to-date" on COVID-19 vaccination by the CDC definition do not have a lower risk of COVID-19 than those "not up-to-date", bringing into question the value of this risk classification definition.
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