Vaccine efficacy diminished as Delta arose, CDC report shows

The effectiveness of Covid-19 vaccines among front-line workers declined to 66% after the delta variant became dominant, compared with 91% before it arose, according to a report from the Centers for Disease Control and Prevention.

The vaccines are still protective, the CDC said. The finding must be interpreted with caution, as vaccine effectiveness might wane over time and the estimates of efficacy were imprecise. "Although these interim findings suggest a moderate reduction in the effectiveness of Covid-19 vaccines in preventing infection, the sustained two-thirds reduction in infection risk underscores the continued importance and benefits of Covid-19 vaccination,” researchers wrote in the CDC’s Morbidity and Mortality Weekly Report.