CDC Halts Publication of COVID-19 Vaccine Effectiveness Study Over Methodological Concerns

On April 23, 2026, U.S. Health officials confirmed the decision to halt the publication of a study examining the effectiveness of COVID-19 vaccines in preventing hospitalizations among adults. The research, which had undergone scientific review and received editorial approval for publication in the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report (MMWR), was withdrawn due to concerns about its methodological approach.

A spokesperson for the U.S. Department of Health and Human Services stated that the MMWR’s editorial assessment identified issues with the study’s methodology for estimating vaccine effectiveness, leading to the decision not to proceed with publication. The report noted that scientific reports are routinely reviewed at multiple levels to ensure they meet the highest standards before release.

The delay and subsequent cancellation were initially reported by The Washington Post, following concerns raised by the CDC’s acting director, Dr. Jay Bhattacharya. According to officials, Dr. Bhattacharya expressed reservations about the method used to calculate vaccine effectiveness in the study. An HHS official confirmed that the study’s authors did not wish to revise their methodology in response to the feedback.

The study in question employed a test-negative case-control design, a method commonly used in observational research to evaluate vaccine effectiveness. This approach compares individuals who test positive for a disease (cases) with those who test negative (controls), assessing differences in vaccination status between the groups. Dr. Bhattacharya specifically criticized this design, stating it would not produce an unbiased estimate of vaccine efficacy.

This development occurred while Dr. Bhattacharya serves in an acting capacity as CDC director, pending Senate consideration of President Donald Trump’s nominee for the permanent role, Dr. Erica Schwartz. Her nomination has drawn attention due to her prior involvement in vaccine mandate discussions during her service at the U.S. Coast Guard.

The incident highlights the ongoing scrutiny surrounding vaccine research and the importance of methodological rigor in public health publications. As of the date of this report, no further details about the study’s findings or potential alternative publication avenues have been made available by the CDC or HHS.