A study demonstrating that Covid-19 vaccines reduced the risk of severe illness by roughly 50% was published in JAMA Network Open on Tuesday, months after being blocked from the Centers for Disease Control and Prevention’s (CDC) own publication. The research, which analyzed data from seven states, found that vaccination lowered the odds of emergency department and urgent care visits by 50% and hospitalizations by 55% during the previous fall and winter. The study had been slated for the CDC’s Morbidity and Mortality Weekly Report (MMWR) in March before acting director Jay Bhattacharya intervened to halt its release.
Why was the study blocked from the CDC publication?
Acting CDC director Jay Bhattacharya blocked the study due to concerns regarding its methodology, specifically the use of a “test-negative design,” according to reporting by NBC News. This research model compares the vaccination status of patients who test positive for a disease against those who test negative. While the study had already cleared the MMWR’s internal scientific review process, Bhattacharya argued that longitudinal cohort studies—which track vaccinated and unvaccinated individuals over time—provide a more robust evidentiary standard. In an op-ed for The Washington Post, Bhattacharya stated that the test-negative design could result in overestimates or underestimates of vaccine effectiveness, noting that the approach fails to account for individuals who were never hospitalized or those with prior infections.
How does the medical community view the test-negative design?
Many public health researchers defend the test-negative design as a practical and industry-standard tool for real-world vaccine evaluation. Natalie Dean, an associate professor of biostatistics at Emory University’s Rollins School of Public Health, noted that the methodology has been used for decades and that its limitations are well-understood by the scientific community. In an editorial published alongside the JAMA Network Open study, Dean characterized the approach as an “important and practical” method. She argued that while the design has limitations—such as the potential for bias if vaccinated individuals are more likely to seek medical care—it does not invalidate the study’s conclusions. Dean, who participated in the peer review for the JAMA publication, stated that the quality of the data remained consistent throughout the review process.
What are the implications for future public health reporting?
The delay of the study has sparked a debate over political influence in federal health agencies. Some public health experts expressed concern that blocking peer-reviewed research could be viewed as an attempt to withhold evidence of vaccine safety, particularly given the administration’s stated skepticism toward vaccines. Emily Hilliard, a spokesperson for the Department of Health and Human Services, defended the agency’s actions, stating that the CDC must apply the “highest standards of scientific rigor” when findings might influence clinical decisions. The tension highlights a divide between those who prioritize rapid, real-world data and those who advocate for longer-term, longitudinal studies as the only acceptable standard for public guidance.
The test-negative design is frequently used for influenza vaccine studies because it effectively controls for “health-seeking behavior”—the tendency for vaccinated people to visit doctors more often than the unvaccinated.
Frequently Asked Questions
- What did the JAMA study conclude about Covid vaccines? The study found that the 2025-26 vaccine formulation reduced the likelihood of Covid-related urgent care or ER visits by 50% and hospitalizations by 55%.
- Why was the study initially pulled from the CDC’s MMWR? Acting director Jay Bhattacharya cited concerns over the “test-negative” methodology, preferring longitudinal studies instead.
- Is the test-negative design considered reliable? Most experts, including those at Emory University, view it as a valid, cost-effective tool for timely real-world analysis, provided its limitations are acknowledged.
- Where can I find the full study? The peer-reviewed paper was published in the journal JAMA Network Open.
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