• Posted April 10, 2026

CDC Pauses Release of COVID Vaccine Effectiveness Study

A health report on COVID-19 vaccines has been delayed after concerns about how the study was conducted.

The report, from the U.S. Centers for Disease Control and Prevention (CDC), found that COVID vaccines reduced emergency room visits and hospital stays last winter.

But release of the report was postponed by Dr. Jay Bhattacharya, who was serving as the agency’s acting director at the time.

A report summary obtained by The New York Times indicated that the study showed that vaccination:

• Reduced emergency visits by 50%

• Reduced hospitalizations by 55%

“Dr. Bhattacharya expressed concerns about the observational method used in this study to calculate vaccine effectiveness, and the scientific team is working to address these concerns,” Andrew Nixon, a spokesman for the U.S. Department of Health and Human Services (HHS), told The Times in an email.

He said the review was routine.

“Dr. Bhattacharya wants to make sure that the paper uses the most appropriate methodology for such a study," Nixon said.

The findings were slated for publication March 19 in the CDC’s Morbidity and Mortality Weekly Report (MMWR).

A few experts said the delay is unusual.

“A political appointee at CDC would be very rarely involved in a review or decision regarding MMWR,” Dr. Debra Houry told The Times. She served as the CDC’s chief medical officer before resigning in August.

“Previously this would have been reviewed by a career scientist who worked across administrations,” she added. 

Amid ongoing health threats like measles, staffing shortages and Bhattacharaya heading up the National Institutes of Health, this would be even more unusual, Houry said.

Observational studies are commonly used to measure vaccine effectiveness.

Bhattacharya has suggested using randomized clinical trials instead, where some participants receive the vaccine and others receive a placebo.

However, experts say those trials are often expensive and difficult to conduct quickly.

More information

The U.S. Centers for Disease Control and Prevention has more on vaccine effectiveness.

SOURCE: The New York Times, April 9, 2026