An HHS spokesperson said Dr. Jay Bhattacharya had concerns about the paper’s methodology. Some current or former CDC employees worry about political interference

The CDC was expected last month to publish a study showing that Covid vaccines reduced the likelihood of severe illness, but the agency’s acting director, Dr. Jay Bhattacharya, delayed its release due to concerns about the methodology.

The study was scheduled to come out in the Centers for Disease Control and Prevention’s flagship scientific publication, the Morbidity and Mortality Weekly Report (MMWR). But Andrew Nixon, a spokesperson for the Department of Health and Human Services, said in an email that Bhattacharya “expressed concerns about the observational method used in this study to calculate vaccine effectiveness.”

“It’s routine for CDC leadership to review and flag concerns about MMWR papers, especially relating to their methodology, leading up to planned publication,” Nixon said. “Dr. Bhattacharya wants to make sure that the paper uses the most appropriate methodology for such a study.”