A group of 12 former leaders of the US Food and Drug Administration (FDA) have shared their worries about proposed changes to vaccine rules in the US. They wrote about this in a recent article in the New England Journal of Medicine. This group includes Robert Califf, the most recent FDA leader. They think the new plans, suggested by the current director of a part of the FDA called CBER, Vinay Prasad, could weaken the rules that help make sure vaccines are safe and effective. The article is a response to a memo sent by Prasad to FDA staff last week. This memo suggests several changes that could greatly alter vaccine rules in the US. If these changes are made, the former leaders say they could disrupt important policies about making and updating vaccines, and could not be in the public’s best interest. One of the main ideas in Prasad’s memo is to stop using a method called ‘immunobridging’ for vaccines that are well-understood and have a lot of safety data. This method uses certain markers to guess how effective a new vaccine might be, which can help speed up access to new vaccines when there’s a public health need, like during the Covid-19 pandemic. The former leaders say getting rid of this method would make it much harder to approve new vaccines, which could slow down the process of replacing old vaccines with better ones, and could also add costs, especially for small biotechnology companies. Prasad’s memo also suggests that scientific debates should happen inside the agency, and calls those who express concerns about the agency’s processes or decisions illegal and unethical. The former leaders say this approach would avoid public transparency. The motivation for these big changes comes from claims by the FDA that Covid-19 vaccines caused the deaths of ten children. The agency has not shared all the details of the studies it used to identify these deaths or the analysis it used to link the vaccines to the deaths. Speaking to Fox News, the current FDA leader, Marty Makary, said: ‘This was data that was gathered during the Biden administration—they did not make it public. We’re going to make that information available.’ Earlier this week, Tracy Beth Høeg, who led an investigation into Covid-19 vaccine safety over mid-2025, was appointed director of the FDA’s Center for Drug Evaluation and Research (CDER). She co-authored a paper with Makary on the risks of Covid-19 vaccine boosters for young adults in 2022. US Health Secretary Robert F Kennedy (RFK) Jr overhauled the Centers for Disease Control and Prevention’s (CDC’s) vaccine committee this year, replacing members with well-known vaccine skeptics and individuals who were critical of both the Covid-19 vaccines and related countermeasures such as lockdowns. These changes were part of a wider initiative from the Trump administration on decreasing reliance on vaccines for respiratory diseases. In a comment piece published in JAMA in June 2025, 17 former Advisory Committee (AdCom) on Immunization Practices (ACIP) members warned that the American immunization program was significantly weakened due to the sweeping regulatory changes. With the commissioners’ comment article taking aim at the FDA, health leaders under the Trump administration are navigating an intense period of criticism. The commissioners concluded in the journal, ‘If the goal is to rebuild confidence, the answer is not to toss aside the basic rules of science, stifle argument and oversight, or supplant expert scientific inquiry for the unilateral decision-making of a few individuals. It is to insist on open deliberation, solid evidence, and procedures the public can see and trust.’