A COVID-19 vaccine study that the CDC's chief halted this spring was published in JAMA Network Open, a leading peer-reviewed medical journal, after being blocked from the CDC's own scientific report. The analysis found that the vaccine reduced the risk of emergency department visits and hospitalizations among healthy adults by about 50% during the 2025-26 winter season, consistent with findings from previous years.

What Happened to the Study?

The research was originally scheduled for publication in March in the CDC's Morbidity and Mortality Weekly Report (MMWR), the agency's official weekly scientific publication. However, Jay Bhattacharya, the CDC's interim director, delayed the study over concerns about the methodology used to calculate vaccine effectiveness. The paper was ultimately not published in the MMWR at all, according to reporting by The Washington Post.

The study's authors and independent experts have questioned whether the methodological concerns were the real reason for the block. Michelle Barron, one of the study's authors and senior medical director of infection prevention and control for UCHealth, a nonprofit health system in Colorado, stated that the decision appeared politically motivated rather than scientifically justified.

"Science was never the issue. Certainly it was within the CDC's purview to keep it out, for whatever reason, but it was clearly not for scientific reasons that the study was withheld from publication in the MMWR," said Michelle Barron.

Michelle Barron, Senior Medical Director of Infection Prevention and Control, UCHealth

Barron suggested the study was blocked because its findings did not align with Health Secretary Robert F. Kennedy Jr.'s agenda to limit COVID vaccine use. Kennedy, founder of a prominent anti-vaccine group, has been an outspoken critic of COVID shots, once calling them the "deadliest vaccine ever made".

Barron

What Did the Research Actually Show?

The study analyzed data from a CDC-funded surveillance network comparing outcomes between healthy adults who received the updated 2025-26 COVID-19 vaccine and those who did not. Between September and December of the previous year, vaccinated adults who sought medical care for COVID-like symptoms had significantly better outcomes than unvaccinated adults.

• Emergency Department Visits: Healthy adults who received the COVID-19 vaccine reduced their likelihood of emergency department and urgent care visits by 50% compared with those not receiving a 2025-26 vaccine dose.
• Hospitalizations: Vaccinated adults cut the likelihood of COVID-associated hospitalizations by 55% compared with unvaccinated adults.
• Study Population: Researchers compared data on adults who sought medical care for COVID-like symptoms, analyzing outcomes between vaccinated and unvaccinated groups.

Why the Methodology Matters

The study used a research approach called test negative design, which the CDC's interim director had criticized. However, independent experts say this methodology is well-established and appropriate for vaccine surveillance. Natalie Dean, associate professor of biostatistics and epidemiology at Emory University's Rollins School of Public Health, defended the approach in a commentary accompanying the journal publication.

"This is not a controversial study design. This is the same design that has been churning out vaccine results for a long time, and from a highly experienced group: CDC plus a network of top vaccine researchers across the country. They are a well-oiled machine," explained Natalie Dean.

Natalie Dean, Associate Professor of Biostatistics and Epidemiology, Emory University's Rollins School of Public Health

Dean emphasized that the methodology has known limitations, like any study design, but those shortcomings are well understood and actively studied. The practical benefits of the approach for routine vaccine-effectiveness monitoring outweigh its limitations, she noted.

What Are the Broader Implications?

The controversy highlights concerns about political interference in scientific research at federal health agencies. Dean warned that efforts to discard the test negative design methodology could weaken the nation's vaccine surveillance system for multiple respiratory viruses.

"There was no scientific reason to reject this paper. It had undergone internal review, and it clearly meets the standards of peer-reviewed science. It makes my colleagues on edge to see political interference in the scientific process," stated Natalie Dean.

Natalie Dean, Associate Professor of Biostatistics and Epidemiology, Emory University's Rollins School of Public Health

Dean added that if the methodology is abandoned, "we'll be flying blind with respect to influenza, COVID and RSV vaccine monitoring." RSV, or respiratory syncytial virus, is another respiratory illness that circulates seasonally and can cause severe disease in vulnerable populations.

Dean

The Health and Human Services Department defended the CDC's review process, stating that the agency evaluates studies using rigorous scientific methods and reviews methodological concerns before publication. A spokeswoman said the CDC does not make scientific determinations based on predetermined conclusions, though she did not directly address the allegation that the paper was withheld due to the administration's vaccine agenda.

The publication of the study in JAMA Network Open, one of the most respected peer-reviewed medical journals, validates the research and its findings. The decision to publish the work despite the CDC's initial block underscores the importance of independent scientific review in maintaining public trust in vaccine safety and effectiveness data.