The Centers for Disease Control and Prevention has delayed publication of a report examining the effectiveness of the COVID-19 vaccine, according to scientists familiar with the matter, raising questions about internal review processes within the agency.

The report, which had been scheduled for release on March 19 in the CDC’s Morbidity and Mortality Weekly Report, found that healthy adults who received the 2025–2026 COVID vaccine were significantly less likely to require emergency or urgent care and hospitalization compared to those who were not vaccinated. According to a summary obtained by The Washington Post, the reduction was estimated at roughly 50% for emergency visits and 55% for hospitalizations.

Despite clearing the agency’s scientific review process, acting CDC Director Jay Bhattacharya reportedly delayed publication due to concerns about the study’s methodology. A spokesperson for the Department of Health and Human Services said it is routine for leadership to review such reports and flag potential issues before release, noting that questions were raised about the observational methods used to calculate effectiveness.

The study relied on a test-negative design, a method commonly used by the CDC and other researchers to evaluate vaccines for respiratory illnesses in real-world conditions. Former CDC official Dan Jernigan said the approach, while not without limitations, has been widely applied in past research.

The delay comes as federal health policy continues to evolve under Health and Human Services Secretary Robert F. Kennedy Jr., who has previously expressed skepticism about COVID vaccines and called for changes in how they are administered and recommended.

Officials said the scientific team is working to address the methodological concerns, though it remains unclear when or if the report will be published.