Under Health Secretary Robert F. Kennedy Jr., who has a long history of anti-vaccine activism, CDC leadership blocked the agency's own scientists from publishing a vetted study finding significant benefits from this season's COVID-19 vaccines.
The study went through the CDC's standard scientific review process and was slated for publication on March 19 in the Morbidity and Mortality Weekly Report (MMWR). According to a summary obtained by The Washington Post, it found that healthy adults who received the 2025-2026 COVID vaccine saw the risk of emergency department or urgent care visits cut by 50% and the risk of COVID-associated hospitalization cut by 55%, compared with adults who did not get this season's shot.
Acting CDC director Jay Bhattacharya held the study, citing concerns about its “test-negative” design, a well-established method the CDC has long used to evaluate vaccine effectiveness for respiratory viruses. The CDC had published a study of this year's flu vaccine using the same design in MMWR a week before the COVID study was set to run.
CDC scientists spoke to The Washington Post on the condition of anonymity for fear of retaliation from the Trump administration. Dan Jernigan, who headed the CDC's influenza division for six years and resigned in protest of Kennedy's political interference at the agency, told the Post: “The secretary has already taken steps to try and remove the availability of the vaccine from children and others, so if you're putting out an MMWR that the vaccine is effective at preventing hospitalizations and medical care visits … that message is not in line with the direction you've been taking with the removal of the vaccine.”
HHS spokesperson Andrew Nixon said, “It's routine for CDC leadership to review and flag concerns about MMWR papers, especially relating to their methodology, leading up to planned publication.” On April 22, the agency confirmed the study would not run. Nixon said, “The MMWR's editorial assessment identified concerns regarding the methodological approach to estimating vaccine effectiveness and the manuscript was not accepted for publication.” Demetre Daskalakis, the former director of the CDC's National Center for Immunization and Respiratory Diseases, told CIDRAP the decision appeared to be “cherry picking based on the bias of the director and others at HHS who don't fully understand the importance of the methods used to assess the added benefit of vaccines in preventing poor outcomes.”
Update (October 2, 2026): On June 23, 2026, the study was published in JAMA Network Open, a peer-reviewed journal from the American Medical Association, NBC News reported. It found the vaccine lowered the odds of a COVID-related ER or urgent care visit by 50% and of COVID hospitalization by 55%. Bhattacharya told NBC News he views longitudinal cohort studies as “a stronger design.” Natalie Dean, an Emory University biostatistician who took part in the journal's peer review, said, “It just feels funny that this has become the difference between whether or not something makes it out in MMWR.”
Correction (October 2, 2026): This entry previously said the study had been permanently suppressed and would not be published. The CDC did refuse to publish it in MMWR, but the study was published in JAMA Network Open on June 23, 2026; those claims have been removed. We also removed an unsourced claim that Kennedy had stripped 6 of 17 childhood vaccines from the recommended schedule, and an assertion that no one blocked the flu study, which the sources do not address beyond noting that it was published.