CDC Delays Covid Vaccine Study Release

Last month, the CDC was anticipated to publish a study indicating that Covid vaccines significantly lower the chances of severe illness. However, Dr. Jay Bhattacharya, the agency’s acting director, postponed its release due to methodological concerns.

This study was meant to appear in the CDC’s leading scientific journal, the Morbidity and Mortality Weekly Report (MMWR). In an email, Andrew Nixon, a spokesperson for the Department of Health and Human Services, noted that Bhattacharya raised issues regarding the observational method employed to assess vaccine effectiveness.

“It’s not uncommon for CDC leadership to review and highlight concerns about MMWR articles, particularly concerning their methodologies,” Nixon explained. “Dr. Bhattacharya aims to ensure the paper utilizes the most suitable method for the research.”

Some health officials from the Trump administration have criticized the standard practices in vaccine research, raising doubts about methods long accepted by scientists. Many public health experts suggest this may be part of a broader strategy to undermine vaccine safety and limit vaccine access.

While the Trump administration claims to restore what it refers to as “gold-standard science” to health agencies, critics argue the intention might be to discredit studies that conflict with its vaccine stance. Health Secretary Robert F. Kennedy Jr., who oversees agencies like the CDC, has a known history of opposing vaccines.

Dr. Bhattacharya, who was appointed as the acting head of the CDC in February and awaits a permanent nomination from Trump, did not provide any comments when approached.

A preliminary overview of the study’s findings, seen by NBC News, pointed to the 2025-26 Covid vaccine formulation reducing the risk of severe illness by approximately 50% among adults.

A CDC epidemiologist, who requested anonymity due to job security concerns, mentioned the paper was expected to be released on March 19.

The Washington Post was the first to report on this delay.

According to the epidemiologist and two former CDC staff members, it’s unusual for a political appointee like Bhattacharya to halt an MMWR paper that has successfully undergone the scientific review process and received approval from the journal’s editors.

While there have been instances of delaying MMWR publications under the Trump administration, it’s rare for a single report to be completely withdrawn. The CDC previously halted certain papers in January 2025 when the administration enforced a communication freeze and faced a temporary shut down due to government issues later on.

“I’m not suggesting there haven’t been other publication stoppages or forced changes, but to entirely block this report’s release, given its well-established platform and methodology, marks a new level of political interference in the CDC’s scientific operations,” remarked Fiona Havers, a former CDC medical epidemiologist who managed the agency’s Covid hospitalization data.

Havers stepped down from the CDC in protest in June after Kennedy dismissed the agency’s vaccine advisory committee to appoint a new group, many of whom had skeptical views on vaccines. A judge later ruled that most of Kennedy’s appointees were unqualified and placed their nominations on hold.

The study in question, which faced scrutiny from Bhattacharya, employed a method known as a test-negative design. This approach involved comparing the vaccination statuses of individuals who tested positive for Covid against those who tested negative, demonstrating that vaccinated individuals had lower hospitalization or emergency department visit rates. Efforts to contact several of the journal’s editors and at least two authors of the paper were unsuccessful.

Current and former CDC workers said this method is a typical way to gauge vaccine effectiveness. Many other MMWR articles, including recent reports on flu vaccination effectiveness and Covid vaccine efficacy in children, have utilized the same approach. An HHS official stated that Bhattacharya had not assumed his acting role in time to vet the flu vaccine paper but would have voiced similar concerns.

Alternative methodologies can often be too costly or may not yield timely results, noted experts from the CDC. For instance, a cohort study—tracking vaccinated versus unvaccinated individuals over time—tends to be far more expensive and usually demands larger sample sizes and extended follow-up periods.

Some leading health officials have advocated for increased randomized controlled trials, which would compare vaccinated individuals to those receiving placebos. However, implementing such trials for Covid vaccines raises ethical dilemmas as it would necessitate withholding approved vaccines from certain participants. The initial Covid vaccines underwent randomized controlled trials, and the data led to FDA approval.

“You can’t conduct randomized controlled trials every year once a vaccine has been approved and confirmed as effective,” Havers commented.

The CDC epidemiologist mentioned a presentation was given in late March at Bhattacharya’s request, clarifying the test-negative design and discussing why other methods weren’t as effective. As of now, clarity regarding the study’s publication timeline remains elusive.

If the paper is ultimately not published in MMWR, its authors may still consider submitting it to an independent medical journal.

Nixon stated that the CDC actively engages in scientific discussions regarding the best ways to quantify vaccine effectiveness in its publications, emphasizing that ensuring the soundness of analyses is preferable to the risk of errors.

He also added that the agency is dedicated to timely publication and transparency about the data and methodologies that support its conclusions.