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Acting CDC Director Delays Publication of Study on Covid Vaccine Effectiveness
The acting director of the Centers for Disease Control and Prevention delayed the release of a study demonstrating that the 2025-26 Covid vaccine formulation reduced severe illness by about half among adults. The study, prepared for the agency's Morbidity and Mortality Weekly Report, employed a test-negative design methodology.
Apr 10, 6:31 PM·2m read3 sources
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The Centers for Disease Control and Prevention expected to publish a study in March 2025 showing that a Covid vaccine formulation reduced the likelihood of severe illness among adults. An acting CDC director delayed the release due to concerns about the study's methodology.
The study was scheduled for the agency's flagship publication, the Morbidity and Mortality Weekly Report. A spokesperson for the Department of Health and Human Services stated that the acting director expressed concerns about the observational method used to calculate vaccine effectiveness.
The spokesperson noted that it is routine for CDC leadership to review and flag concerns about Morbidity and Mortality Weekly Report papers, particularly regarding methodology, before planned publication.
The acting director sought to ensure the paper used the most appropriate methodology. The acting director, a political appointee, assumed the role until a permanent director is nominated. The study relied on a test-negative design, comparing vaccination status among people who tested positive for Covid with those who tested negative.
This approach showed that vaccinated individuals were less likely to be hospitalized or visit emergency departments.
Current and former CDC employees described the test-negative design as a common method for evaluating vaccine effectiveness.
Other Morbidity and Mortality Weekly Report papers, including a report on seasonal flu shots and a report on Covid vaccines in children, used the same methodology. An official indicated that the acting director would have raised similar concerns about the flu vaccine paper if reviewed in time.
Alternative methodologies, such as cohort studies tracking vaccinated and unvaccinated groups over time, require larger sample sizes, longer follow-up periods, and higher costs.
