After the Centers for Disease Control and Prevention (CDC) was expected to release a study showing that COVID-19 vaccines reduce the risk of severe illness, NBC News reports that acting director Dr. Jay Bhattacharya pushed the pause button, citing concerns about the methodology.
Scheduled for a March 2026 release, the study came from the CDC’s flagship scientific publication, the Morbidity and Mortality Weekly Report (MMWR). But spokesperson Andrew Nixon said 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.”
According to The Hill, the report focused on the vaccine’s effectiveness in reducing hospitalizations and emergency department visits among healthy adults during the 2025 winter season. However, the methodology being questioned by the agency’s director has been used for years to determine vaccine effectiveness against respiratory viruses and was also used by the New England Journal of Medicine in a 2021 study focusing on the same topics.
In what Bhattacharya labeled an “observational method,” the study uses a test-negative design that examines individuals who are sick enough to seek care, be tested and then give consent, with their vaccination rates compared to those who test positive versus those who do not.
Bhattacharya was appointed to run the CDC back in February until President Donald Trump nominates a permanent director. Leading health officials in the Trump administration have criticized how vaccine research is typically conducted, questioning methods that have long been used and are widely accepted among scientists.
Many public health experts, like Dr. Fiona Havers, a former medical epidemiologist who resigned from the CDC in protest after HHS Secretary Robert F. Kennedy Jr. fired the agency’s vaccine advisory committee and appointed a new group, see the delay as part of a broader effort to push narratives of doubt in vaccine safety and make them less available to those who need them. “I’m not saying that they haven’t stopped other publications or forced changes to them, but to wholesale stop this report from coming out, given that it is such a well-established platform and such a well-established methodology, does strike me as a new level of political interference into CDC’s scientific process,” Havers said.
The prospect of political interference could be supported by former Food and Drug Administration (FDA) regulator Vinay Prasad’s call for new restrictions on approved COVID-19 vaccines from Novavax and Moderna. The move caused controversy, which, as a result, pushed the announcement that guidelines on vaccine approval would become more stringent following the deaths of 10 children who allegedly died “after and because of a” COVID-19 vaccine.
However, Nixon insists the delay is simply because “Dr. Bhattacharya wants to make sure that the paper uses the most appropriate methodology for such a study” and the CDC “taking time to ensure analyses are methodologically sound and clearly communicated is always preferable to risking error.”
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