As Delta spread, Covid-19 vaccine effectiveness against infection fell from 90% to 66% in one key study
Source: Stat News
The effectiveness of Covid-19 vaccines at preventing infection fell in one study of U.S. frontline workers from roughly 90% to 66% as the Delta variant emerged and became dominant in the country, an updated report from the Centers for Disease Control and Prevention released Tuesday indicated.
The study, known as HEROES-RECOVER, includes more than 4,000 health care workers, first responders, and other frontline workers in eight locations across six states, all of whom have been tested weekly for infection with SARS-CoV-2. More than 4 in 5 were vaccinated, and the vast majority of them received the mRNA vaccines from either Pfizer-BioNTech or Moderna.
Researchers had previously reported that from Dec. 14, 2020, when the vaccines started rolling out, to April 10, 2021, the vaccines were approximately 91% effective at preventing both symptomatic and asymptomatic infection from SARS-2. The finding underlined the ability of the vaccines to halt infection entirely and slash transmission; the clinical trials that led to the authorization of the vaccines had generally focused on their effectiveness at preventing symptomatic Covid-19 cases.