CDC MMWR: during Delta, prior infection protected more than vaccination alone; hybrid protection highest

CDC and the California and New York health departments published an MMWR analysis of statewide case, hospitalization, and immunization data from May–November 2021 across four adult cohorts. Before Delta became predominant (June–July 2021), case rates were lowest among vaccinated people without a prior diagnosis; by the week of October 3, case rates were substantially lower in both cohorts with prior infection, and lowest among people with both vaccination and prior infection, while unvaccinated people without a prior diagnosis always had the highest case and hospitalization rates. In an accompanying statement, CDC stressed the analysis predated Omicron and widespread boosters, did not account for the risks of the initial infection, and maintained that vaccination remains the safest strategy.