The top vaccine regulator at the Food and Drug Administration (FDA) wants to impose vague but sweeping new standards on vaccine testing that, health experts say, would impede the development of new immunizations and likely curtail access to life-saving shots, according to a memo sent to staff on October 28.

Vinay Prasad, MD, director of the FDA’s Center for Biologics Evaluation and Research (CBER), proposed the “path forward” in an internal memo in which he claimed—but provided no evidence—that COVID-19 vaccines caused the death of 10 children. 

Many infectious disease experts say Prasad should share the evidence on which he based his argument. Linking a vaccine to an adverse event requires a high level of evidence, including autopsy results and medical records that rule out other causes of death and show whether the affected person was infected with the coronavirus itself, said Paul Offit, MD, an infectious disease specialist at Children’s Hospital of Philadelphia and co-inventor of a rotavirus vaccine.

Prasad is “making a fairly fantastic statement,” Offit said. “He should provide extraordinary evidence that that’s clear, and he didn’t, which is incredibly irresponsible and unprofessional to do.”

In the memo, Prasad wrote that the FDA’s current vaccine approval process falls short.

He should provide extraordinary evidence that that’s clear, and he didn’t, which is incredibly irresponsible and unprofessional to do.

In the future, the FDA will “demand pre-market randomized trials assessing clinical endpoints for most new products,” including vaccines, Prasad wrote. He noted that COVID-19 vaccines have not been tested in randomized controlled trials (RCTs) in pregnant women. Such trials are the most rigorous type of study, but they can cost millions of dollars and take years to produce results.

“We will not be granting marketing authorization to vaccines in pregnant women” without such evidence, Prasad wrote. The memo’s contents were first reported by a PBS News correspondent in a series of posts on X, the social media platform.

Asking for the impossible

Demanding an RCT would prevent pregnant women from receiving most vaccines, said Jake Scott, MD, a clinical associate professor of infectious disease and geographic medicine at Stanford University School of Medicine.

That’s because pregnant women are almost never included in RCTs of vaccines or other drugs due to potential risks to the fetus, Scott said. Instead, the FDA does careful safety monitoring and measures antibody levels in women’s blood, which can show whether the vaccine is generating an immune response.

In his memo, Prasad also wrote that “pneumonia vaccine makers will have to show their products reduce pneumonia,” at least after they’re licensed, rather than provide indirect evidence of protection, such as antibody levels.

Prasad appears to refer to a childhood pneumonia vaccine that blocks infections with pneumococcus bacteria, which has been updated and improved several times over the years, said Dorit Reiss, PhD, a law professor at the University of California Law, San Francisco. Although the first version of the vaccine protected children from seven bacterial strains, the latest iteration protects against 20 strains.

Pneumococcal vaccines on the market today are approved based on antibody levels that correlate with protection and have been validated over decades, Scott said.

Proving that childhood vaccines prevent cases of pneumonia would be difficult, Scott said, because so many pathogens can cause pneumonia, including the flu, COVID-19 and respiratory syncytial virus (RSV).

It would be unethical to use placebos and let people get pneumococcal pneumonia.

Requiring manufacturers to conduct additional clinical trials every time they want to add additional viral or bacterial strains would delay updates by several years, all the while leaving people vulnerable to the bacteria, Reiss said. Some companies may decide that conducting such trials is too expensive.

“You’d need massive, expensive trials that many companies won’t pursue,” Scott said.

Conducting RCTs of proven vaccines could also be unethical, said Jesse Goodman, MD, who previously filled Prasad’s role at the FDA and now directs Georgetown University’s Center on Medical Product Access, Safety and Stewardship.

“It would be unethical to use placebos and let people get pneumococcal pneumonia,” Goodman said.

Flu vaccines also in crosshairs

Prasad’s memo was also extremely critical of flu vaccine testing.

But performing large clinical trials on each year’s influenza vaccines before the start of flu season would be impossible, Scott said. Although vaccines are made the same way every year, the viral strains used to produce them typically change each year, based on the viruses in circulating. Scientists make their best guess about which strains to include in Northern Hemisphere vaccines in February or March, because manufacturing them takes six months. 

Requiring any additional testing could prevent the vaccines from being ready for the flu season, which begins in the fall in the Northern Hemisphere.

Reiss said Prasad is correct when he says that flu shots get minimal testing.

“But it’s minimal testing for a reason,” she said. “If you’re demanding more, you’re making it almost impossible to approve an annual vaccine. He didn’t tell us exactly in detail what the FDA is going to say, but is this is going to demand a large clinical trial every year. That’s just not going to happen.”

Conducting an RCT of each season’s flu vaccine would be impossible, Scott said, given that these studies typically take several years.

If the FDA requires RCTs for annual flu shots, the results would not be ready until years later, rendering the vaccines worthless, Scott said.

Prasad issued his memo just days before a two-day meeting of the Center for Disease Control and Prevention’s (CDC’s) influential vaccine committee, which is scheduled to be held Thursday and Friday. The Advisory Committee on Immunization Practices recommends which vaccines Americans should receive, and its decisions influence which vaccines are covered by insurance or federal programs.

Many researchers told CIDRAP News they fear that the committee could use Prasad’s memo to justify further restrictions on vaccines.

“Even if vaccines remain technically available,” Scott said, “without CDC recommendations or insurance coverage, access disappears. It’s a de facto ban disguised as higher standards.”

“The [influenza] virus has proven far more dangerous to children than any documented vaccine risk,” Scott said.

Ignoring benefits of COVID-19 vaccines

Prasad’s memo focuses only on the potential risks of vaccines, without considering their benefits or citing how many lives they have saved, said Angela Rasmussen, PhD, a virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan.

In his memo, Prasad harshly criticized the FDA for authorizing COVID-19 vaccines for children, as well as the CDC, which encouraged kids to receive the shots.

“Healthy young children who faced tremendously low risk of death were coerced, at the behest of the Biden administration, via school and work mandates, to receive a vaccine,” Prasad wrote.

It’s a de facto ban disguised as higher standards.

Research shows that COVID-19 caused 1,642 deaths in children from 2020 to June 2023. Even by conservative estimates, vaccines saved the lives of 299 children from 2020 to 2024.

Demetre Daskalakis, MD, who led the CDC’s National Center for Immunization and Respiratory Diseases in August, defended the agency’s actions during the pandemic, noting that policy makers often must make public health decisions based on incomplete or imperfect information.

“The quest for perfect data to make decisions is not feasible,” said Daskalakis, who resigned from the CDC in August after Health and Human Services Secretary Robert F. Kennedy Jr. fired the agency’s director after less than a month in the position.

“We have to make decisions in public health with the best data available to make recommendations and guidelines that are implementable and realistic and based in the best science,” Daskalaki said. “Creating impossible standards demonstrates a lack of understanding of public health and the role of agencies in balancing risk and benefit.”

Reiss, the legal scholar, said Prasad’s memo is “legally tricky.”

The FDA typically follows an established procedure when making regulations. The agency usually issues a proposed regulation and solicits outside comments from experts and the public before issuing a final rule.

Vaccine manufacturers could sue the FDA, charging that the changes violate federal laws by being “arbitrary and capricious,” Reiss said. Legally, Prasad “needs to have some really good reasons” to make such sweeping changes if he wants them to survive judicial review. “If they decide to sue, they would have some very good arguments about this being arbitrary and capricious” and undermining the ability of companies to rely on the FDA’s word.

The president of the American Academy of Pediatrics said she agrees that vaccines should be rigorously tested.

“Parents deserve transparent communication to make informed decisions,” said Susan Kressly, MD, the academy’s president, in a statement.

“We are concerned that the newly proposed requirements could limit children’s access to safe, proven vaccines,” Kressley said. “The existing approval process already includes robust testing that carefully weighs benefits and risks to protect children. Preserving a strong, science-based framework is critical to ensuring families can continue to access the vaccines they need.”