The US Food and Drug Administration has blocked the publication of several studies that found Covid-19 and shingles vaccines to be safe, according to a spokesperson from the Department of Health and Human Services.

Agency scientists conducted the studies by analyzing millions of patient records and found that serious side-effects from the vaccines were rare, the spokesperson confirmed. The studies – funded by taxpayer money and costing several million dollars – included research examining the safety of Covid-19 vaccines in 2023 and 2024.

Andrew Nixon, an HHS spokesperson, confirmed the withdrawals in a statement, saying: “The studies were withdrawn because the authors drew broad conclusions that were not supported by the underlying data. The FDA acted to protect the integrity of its scientific process and ensure that any work associated with the agency meets its high standards.”

One of the Covid-19 studies examined vaccine safety in people over 65 by reviewing the medical records of 7.5 million Medicare beneficiaries, the New York Times first reported.

Researchers focused on the period 21 days after vaccination and the subsequent 20 days, comparing rates of health issues immediately following vaccination. They assessed 14 potential outcomes, including heart attacks, strokes and Guillain-Barré syndrome, a rare autoimmune disorder, the Times said.

Researchers said anaphylaxis was the only concerning outcome, affecting roughly one in a million people who received the Pfizer vaccine. The study stated: “No other statistically significant elevations in risk were observed,” per the Times. Despite being accepted by Drug Safety, a peer-reviewed journal, the study was later withdrawn, people familiar with the matter told the Times.

“The fact that in one case these were accepted by a journal and that they are open about not liking the conclusion makes it more jarring,” said Dorit Reiss, a law professor at UC Law San Francisco who focuses on vaccine-related legal and policy issues.

Janet Woodcock, the former Food and Drug Administration’s principal deputy commissioner, said that “there is a pattern here for not letting information out that might support the general safety of vaccines, with methodological rationales given by non-scientist spokespersons”, probably referring to Nixon.

Another withdrawn study reviewed by the New York Times examined Covid-19 vaccine safety among 4.2 million people aged six months to 64 years.

That study assessed more than a dozen health conditions – including brain swelling, blood clots and heart attacks – and found rare cases of fever-related seizures and myocarditis, or heart muscle inflammation.

“Given the available evidence, FDA continues to conclude the benefits of vaccination outweigh the risks,” the study said, adding that Angela Rasmussen, editor in chief of the journal Vaccine, confirmed to the Times that the paper was withdrawn by its authors.

In addition to the Covid-19 studies, several shingles studies were also prevented from being published. People familiar with the matter told the New York Times that agency officials did not sign off in time in February for staff to submit abstracts on two Shingrix studies to a drug safety conference. A senior administration official also said the studies were not moving forward at the agency.

In a statement to the Times, Nixon said that “the design of that study fell outside the agency’s purview”. The paper added that the decision to halt the studies’ publications did not reach the FDA commissioner, Marty Makary, or the HHS secretary, Robert F Kennedy Jr.

The Times’ latest report follows mounting backlash against the HHS and its secretary, Robert F Kennedy Jr, who has repeatedly pushed anti-vaccine rhetoric and drastically limited funding and accessibility to Covid-19 vaccines and others.

Meanwhile, employees have raised concerns about management at the FDA under Makary’s leadership, with Bloomberg recently reporting that Makary has frequently clashed with administration officials while biotech firms grow disillusioned by what they view as an inconsistent drug review process.

Melody Schreiber contributed reporting