CDC: Vaccine effectiveness declined amid Delta variant, still protected against severe illness

Exterior of the Centers for Disease Control and Prevention in Atlanta.
Exterior of the Centers for Disease Control and Prevention in Atlanta. Photo credit Jessica McGowan/Getty Images
By , KNX 1070

The Centers for Disease Control and Prevention released three studies Wednesday that show the overall protection against COVID-19 afforded by the vaccines dwindled this summer after the highly contagious Delta variant emerged.

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Even so, researchers found the immune defense provided by the vaccines remained high for months after a person was considered fully vaccinated.

The three studies -- published in the CDC’s weekly scientific digest -- reportedly reinforced the Biden administration’s decision to encourage booster shots for vaccinated people after eight months beginning September 20, the Washington Post reported.

The reports examined vaccine effectiveness, weighing transmission rates, hospitalizations, and deaths among the vaccinated and unvaccinated.

“Examining numerous cohorts through the end of July and early August, three points are now very clear,” said CDC Director Rochelle Walensky during a White House COVID briefing Wednesday. “First, vaccine-induced protection against SARS-CoV-2 infection begins to decrease over time. Second, vaccine effectiveness against severe disease, hospitalization and death remains relatively high. And third, vaccine effectiveness is generally decreased against the delta variant.”

The New York study used public health data and found a slight decrease in vaccine effectiveness, dipping from 92% in May to 80% in late July. In addition, researchers found vaccinated New Yorkers accounted for 20% of new infections and 15% of hospitalizations.

A second study surveying nursing homes nationwide found the vaccines lost some strength amid the delta variant’s surfacing, slipping from 75 percent from March to May to 53 percent in June and July. As a result, the study’s authors strongly recommended “additional doses” for facilities’ residents.

The third report analyzed hospitals from 21 states and concluded vaccines worked to ward of hospitalizations, claiming that for adults without severe underlying health conditions, the vaccine was 90 percent effective.

Decreases in vaccine efficacy “to about 10 percent lower, I would take with a grain of salt,” Maria Sundaram, an epidemiologist and infectious-disease specialist at the University of Toronto, told the Post.

“Vaccines are very, very helpful, but they’re not the end-all, be-all of COVID-19 prevention,” she added, encouraging mask-wearing and other precautions.

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