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People wait in line to receive the COVID-19 vaccine at a vaccination center in New York on Aug. 19. (Xinhua/Yonhap News)

The effectiveness of COVID-19 vaccines produced by Pfizer, Moderna, and Janssen fell collectively from 91% to 66% as the virus’ Delta variant became the predominant strain, study findings show.

The findings were shared by the US Centers for Disease Control and Prevention (CDC) based on a study tracking 4,217 early vaccine recipients and people working in essential workplaces, including medical staff, according to reports Tuesday in the UPI and other overseas news outlets.

A CDC researcher said that the “trend should be interpreted with caution because [vaccine effectiveness] might also be declining as time [passes].”

According to the study, the vaccines collectively showed 91% effectiveness in the initial post-inoculation period from Dec. 14, 2020, to April 10, 2021. But that rate had dropped to 66% by Aug. 14, at which point the Delta variant had become predominant.

“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,” the researchers stressed.

Other research findings released by the CDC that day showed that of the 43,000 people who tested positive for COVID-19 in Los Angeles County, California, between May 1 and July 25, 25% were fully vaccinated and 71% were unvaccinated. Among hospitalized patients, unvaccinated people accounted for 25 times as many cases as fully vaccinated people.

By Park Byong-su, senior staff writer

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