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U.S. health officials have halted the publication of a federal study examining whether COVID-19 vaccines continue to protect adults from severe illness requiring hospitalization, citing concerns over the research methodology.
A spokesperson for the U.S. Department of Health and Human Services confirmed the decision on Wednesday, noting that internal disagreements over how the data was analyzed led to the study being withheld. The report had been slated for release in the Morbidity and Mortality Weekly Report, the flagship journal of the Centers for Disease Control and Prevention.
The study relied on a widely used observational method in vaccine research, focusing on patients admitted to hospitals or treated in emergency departments. Researchers compare vaccination status among those who test positive for COVID-19 against those who do not, using the data to estimate vaccine effectiveness. This approach has been peer-reviewed and published extensively in leading journals such as Pediatrics and The New England Journal of Medicine.
According to reporting by The Washington Post, the now-shelved study found that COVID-19 vaccination reduced emergency room visits and hospitalizations among otherwise healthy adults by roughly 50% during the past winter.
Federal officials did not specify the exact flaws they identified but pointed to potential biases, including prior infection history, behavioral differences, and variations in who seeks medical care. However, some experts dispute those concerns. Fiona Havers, a physician and former CDC official based in Atlanta, noted that the methodology is specifically designed to account for such variables. She added that prior infection is unlikely to significantly skew results given the widespread exposure to the virus across the U.S. population.
Havers also emphasized that while no study design is without limitations, there are few practical and ethical alternatives capable of delivering real-time estimates of vaccine effectiveness on a national scale.
The decision has reignited longstanding concerns about political influence over public health communications. During the first administration of Donald Trump, public health advocates raised alarms about potential interference in the publication process of the MMWR. Similar concerns resurfaced last year when the report’s publication was temporarily suspended following Trump’s return to office, before resuming in a more limited format.
Critics argue that restricting such research could have serious consequences. Dick Durbin, a Democratic senator from Illinois, warned that limiting access to timely, evidence-based public health data undermines the ability of healthcare professionals to respond effectively.
“Health care professionals rely on the MMWR for timely, objective and fact-based information about the nation’s public health,” Durbin said in a statement. “Muzzling scientists and doctors on how to prevent Americans from being hospitalized can have deadly consequences.”