A Trump administration appointee has delayed publication of a Centers for Disease Control and Prevention (CDC) report that shows benefits related to the Covid vaccine, leading to concerns that the administration is engaging in behind-the-scenes tactics to undermine vaccines.

Research by CDC scientists found that the Covid vaccine cut the likelihood of emergency room visits and hospitalizations for healthy adults last winter by about half, according to reporting from the Washington Post. The acting CDC director, Jay Bhattacharya, reportedly delayed the report’s publication due to concerns surrounding the research’s methodology.

The move to postpone the publication of the CDC’s report has raised concerns among experts and former CDC officials about further attacks to the agency’s vaccine-related work by the Trump administration.

Since Trump took office last January, the health secretary, Robert F Kennedy Jr, and his appointees have engaged in public and behind-the-scenes maneuvers to hamper vaccine research and recommendations.

“This is definitely an escalation of this administration’s undermining of CDC science,” said Dr Fiona Havers, a former senior adviser on vaccine policy at the CDC. “The fact that they are now blocking this is extremely concerning.”

Havers resigned from the CDC last year, in response to the Trump administration’s approaches to vaccine policy.

The CDC’s research found that between September and December 2025, healthy adults who received the vaccine reduced their likelihood of Covid-related hospitalizations by 55%, according to the Post’s report. Those who took the vaccine also reduced their likelihood of emergency and urgent care visits by 50%.

The report, which was set to be published on 19 March in the CDC’s scientific journal, is being delayed for questions surrounding its methodology. Bhattacharya, the acting CDC director, is reviewing the report’s methodology and is expected to meet with some of the CDC scientists for further conversations.

The methodology in question has been used for countless studies by the CDC for about two decades, according to Havers and the Post’s reporting. The methodology, known as “test-negative design”, compares patients who are already sick and their vaccination rates. Because CDC policy is to recommend that people take the Covid vaccine, performing a placebo effect test would be unethical, Havers explained.

Just a week before the report was supposed to be published, a separate report about the flu vaccine and its effectiveness was published in the Morbidity and Mortality Weekly Report, the CDC’s journal. That research on the flu vaccine used the same methodology as the Covid research, the Post reported.

“There was nothing new or unexpected about this report and the methods that they used,” said Havers. “That a political appointee stopped it is extremely concerning.”

Kennedy, the health secretary, has been a vocal critic of the Covid vaccines. The administration has attempted to soften its public perception surrounding the Covid-19 vaccines in the lead-up to the 2026 midterms. This latest scandal with the Covid-19 vaccine report suggests the administration is using back-channel and behind-the-scenes maneuvers to push forward its mission.

Kennedy once called the Covid-19 vaccines the “deadliest vaccine ever made”. And last year, he posted a video on social media, ordering that the CDC no longer recommend the Covid-19 vaccine to healthy pregnant women and children.

During the height of the Covid-19 pandemic in 2020, Bhattacharya opposed lockdowns and mask mandates. He was nominated by Trump in 2024 to direct the National Institutes of Health (NIH). He stepped in as CDC director in February of this year.

“It’s routine for CDC leadership to review and flag concerns about MMWR papers, especially relating to their methodology, leading up to planned publication,” a CDC spokesperson told the Washington Post. The spokesperson added that Bhattacharya was concerned about “the observational method used in the study to calculate vaccine effectiveness, and the scientific team is working to address these concerns”.

Kennedy’s appointment to lead the HHS has created a significant shake-up within the department and its multiple agencies. Last year, Kennedy fired all 17 members of a vaccine advisory committee and replaced a few with members who are seemingly also opposed to vaccines.

A number of CDC employees, including Havers, have resigned in protest of Kennedy’s actions.

“The report said something that this administration doesn’t want to have publicized –that the Covid vaccines are effective at preventing severe illness,” said Havers, who resigned last June from the CDC. “It’s behind the scenes – it’s a very dangerous step that they have taken.”