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CDC Study on 2025-26 Covid Vaccine Published in JAMA After Acting Director Blocked MMWR Appearance
A study originally slated for the CDC's MMWR appeared Tuesday in JAMA Network Open after Acting Director Jay Bhattacharya blocked it. The research examined adults across seven states from September to December 2025.
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A CDC study published Tuesday in JAMA Network Open found that the 2025-26 Covid vaccine formulation reduced the odds of a Covid-related emergency or urgent-care visit by 50% and the odds of hospitalization by 55%. The study examined adults who visited hospitals or urgent-care centers with Covid-like symptoms across seven states from September to December 2025.
The paper used a test-negative design that compared vaccination status between people who tested positive for Covid and those who tested negative.
NBC News reported that the study had passed scientific review and editorial approval for the CDC's Morbidity and Mortality Weekly Report before Acting Director Jay Bhattacharya blocked its appearance there. Bhattacharya stated he prefers longitudinal cohort studies over test-negative designs for assessing vaccine effectiveness.
In a Washington Post op-ed he wrote that the test-negative approach disregards data on people who were never hospitalized and that factors such as prior infections could skew results, making it "impossible to tell" whether estimates are over- or underestimates.
HHS spokesperson Emily Hilliard said the CDC requires the highest standards of scientific rigor when findings may influence clinical decisions such as immunization. "Taking time to ensure analyses are methodologically sound and clearly communicated is always preferable to risking error," she added.
The study authors described the test-negative design as "a convenient and efficient method" to evaluate vaccines quickly in real-world settings.
Natalie Dean, who participated in the peer-review process for the JAMA paper, said researchers have long been aware of the design's limitations but generally agree they do not undermine the conclusions. " The study's limitations include that participants seeking hospital or urgent care may be more likely to be vaccinated than the general population and that participants who tested negative had other respiratory illnesses.
