Of all Donald Trump’s conspiratorial obsessions, perhaps one of the most dangerous has been his long promotion of the much-debunked theory that vaccines cause autism.

For years, his distrust of vaccines had been an occasional curiosity of his Twitter feed, nestled between bromides against Rosie O’Donnell and boasts about his ratings on “Celebrity Apprentice.” “Healthy young child goes to doctor, gets pumped with massive shot of many vaccines, doesn't feel good and changes - AUTISM. Many such cases!” he tweeted in March 2014. “I am being proven right about massive vaccinations—the doctors lied. Save our children & their future,” he wrote months later.


Then, during a Republican primary debate in September 2015—well before anyone really thought he could be America’s next president—Trump brought his vaccine beliefs to the national political stage. “You take this little beautiful baby, and you pump—I mean, it looks like just it’s meant for a horse and not for a child,” he said. “We had so many instances, people that work for me, just the other day, 2 years old, a beautiful child, went to have the vaccine and came back and a week later got a tremendous fever, got very, very sick. Now is autistic.”

Each time his beliefs have come up, journalists and the medical and scientific community have dutifully noted that Trump is wrong—the evidence clearly shows no link between vaccines and autism. Now, Trump is going to be the president of the United States, and doctors and scientists are raising the alarm about the potential consequences of having a man in charge of the country’s public health system who dabbles in discredited scientific theories.

Those concerns only grew on Tuesday, when Trump met with Robert F. Kennedy Jr., an environmental lawyer who has long been immersed in those discredited theories. Kennedy told reporters at Trump Tower that he was responding to a summons by the president-elect. His goal in meeting with Trump, he said, was “to make sure we have scientific integrity in the vaccine process for efficacy and safety of vaccines.”

As for Trump, Kennedy said, he “has some doubts about the current vaccine policies and he has questions about it.” He added: “His opinion doesn’t matter but the science does matter and we ought to be reading the science and we ought to be debating the science. And that everybody ought to be able to be assured that the vaccines that we have—he’s very pro-vaccine, as am I—but they’re as safe as they possibly can be.”

For those not steeped in the language of vaccine debates, Kennedy was using a familiar canard: that he’s not anti-vaccine, but rather pro-vaccine safety. In reality, all scientists are for safe vaccines. What Kennedy’s comment really means is that he is unwilling to accept the scientific evidence showing that today’s vaccines are already as safe as they possibly can be.

Which is why the news of the meeting—and Kennedy's subsequent confirmation on Thursday that he will leave his environmental group to chair a vaccine safety commission for the president—has sparked immediate condemnation from experts in the medical and scientific communities, who worry about what Trump’s choice of advisers says about his public health agenda. While the power Trump or any of his aides has to directly influence vaccine policy is limited, a White House team set on questioning established vaccine science does have the potential to cause significant harm to public health by sowing doubts and wasting scientific resources better spent elsewhere. Increasing pockets of vaccine hesitancy and refusal in southern California, helped by outspoken vaccine critics such as Bob Sears, enabled the Disneyland measles outbreak to spread as far as it did, revealed a study several months later. Other studies have shown clear correlations between pertussis and measles outbreaks and higher rates of exemptions that allow parents to opt out of vaccines required for school.

“Clearly Donald Trump has questions about vaccine safety—he made that clear in the first debate—but I still would have imagined he would have sought out some level of expertise,” says Paul Offit, chief of the Division of Infectious Diseases at Children’s Hospital of Philadelphia and co-developer of the rotavirus vaccine. “There is an enormous amount of expertise about vaccines in this country. Instead, he picks [to advise him] two people—Andrew Wakefield and Robert F. Kennedy Jr.—who both have no expertise and, frankly, are conspiracy theorists.” Wakefield is the discredited British researcher who initially tried to link autism with the measles-mumps-rubella virus in a study that was retracted and has since been debunked by dozens more studies. Wakefield, who met with Trump last summer, was found to have committed fraud and lost his medical license, but anti-vaccine advocates believe he was wronged and continue to reject the scientific consensus against his ideas.

Kennedy, an attorney who has no formal scientific or medical training, has actively campaigned against vaccines recommended by the Centers for Disease Control and Prevention (CDC) since the early 2000s, citing a scientifically discredited concern that the preservative thimerosal contained in some vaccines causes neurodevelopmental disorders in children. Thimerosal is a form of ethylmercury used in multi-dose flu vaccines to prevent bacterial or fungal contamination. Ethylmercury, different from the neurotoxin methylmercury found in fish, exits the body within a week or two; but it was removed from all childhood vaccines, except the flu vaccine, in 2000 until further study could be done on its safety. Since then, multiple studies have proven that thimerosal causes no harm in children or adults. The American Academy of Pediatrics provides a summary of a dozen such studies, including a 2013 study showing no harm from multiple vaccines over time, and a comprehensive Institute of Medicine report in 2004.

And yet, Kennedy has remained dogged. He even wrote a 2014 book—titled Thimerosal: Let the Science Speak—on the topic, arguing the chemical is harmful, but the dozens of studies cited in the book either do not support Kennedy’s claims or were authored by discredited researchers. (Kennedy initially agreed to an interview for this story, to clarify the details of his meeting with Trump and what came of it, but later cancelled, stating, “The Transition has asked me to not make any statement for the time being.”)

This kind of disregard for accepted science—and Trump’s embrace of it—has experts in the scientific community worried. Even forming a commission on autism and vaccines without Kennedy’s involvement would be counterproductive at best and harmful at worst, says Mark Schleiss, division director of Pediatric Infectious Diseases at the University of Minnesota in Minneapolis.

“In an era where government has limited resources, any commission given the task of exploring this issue is a complete waste of time, money and resources because this issue is already settled,” Schleiss says. “If thimerosal had been a problem, we would have seen autism rates decline when we took it out of vaccines, and they didn’t. Those are resources that could be directed toward meaningful autism research or toward support for families with autism children.”

Alison Singer, co-founder and president of the Autism Science Foundation, agrees. “We need to devote our scarce resources and our energy to study what really does cause autism,” Singer says. “Instead of doing the 40th study on vaccines, let’s do the first study on something we haven’t studied.”

Singer, mother of a 19-year-old daughter with autism, says she led the charge to study vaccines and autism back in 2000. But those studies conclusively, consistently showed no association between vaccines and autism. And so she accepted the facts and moved on.

“We don’t get to choose our facts, and RFK is unwilling to accept what the data clearly show,” Singer says. “His position is ‘I don’t believe the studies,’ and that’s just not how science is done. That’s a very dangerous position, to say he knows better than all of the scientists and all of the studies. That’s a position that’s a public health threat.”

It all begs the question: How much damage can Trump and his advisers actually do to established vaccine policies and programs from the White House?

Control over vaccine policy is split between the federal government and the states. The CDC’s Advisory Committee on Immunization Practices (ACIP) makes official recommendations on what vaccines different populations should receive. But it’s the states that determine what vaccines are required for school or daycare entry. All states currently require most of the CDC recommended vaccines, with exemptions for those who cannot receive vaccines due to medical conditions or contraindications. And all but three states provide some form of personal belief or religious exemption. Trump, in other words, won’t be able to actually mandate whether children receive vaccines or not.

But there are other ways that he might influence vaccine policy. Offit notes two federal programs that are essential to public health: the National Vaccine Injury Compensation Program (NVICP), which provides compensation for injuries that a vaccine may have caused, and the Vaccines for Children (VFC) program, which ensures that all children have access to vaccines regardless of socioeconomic or insurance status. Both were created by Congress, NVICP in 1986 and VFC in 1993, and would therefore need to be dismantled by Congress. But Trump’s party currently controls both houses of Congress.

“If you disrupt NVICP, that would be deadly,” Offit says. Doing so would mean individuals could sue pharmaceutical companies in civil court. Last time this was possible, in the 1980s, seven of eight drug companies making pertussis vaccine stopped, leading to skyrocketing costs of vaccines and nearly triggering a public health crisis. “The amount they were spending in civil court to defend themselves from lawsuits was exceeding the amount they could make from vaccines,” Offit says, noting that only four companies make vaccines today. “We were about to lose the pertussis vaccine for children because of civil litigation.” That could happen again, Offit says.

Even without Congress on its side, the office of the president has considerable power when it comes to vaccines, explains Daniel Salmon, Ph.D., associate professor and deputy director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health.

“The president has two main powers here. The bully pulpit is probably the biggest: When he speaks, people listen. When this president-elect tweets, people listen,” Salmon says. “Simply by saying something, he can largely impact people’s views and create controversy where it doesn’t exist.”

The second power lies in his role as head of the executive branch, says Salmon, who also served as director of vaccine safety at the National Vaccine Program Office for five years up through 2011.

“The leadership of all the agencies is designated by the president or his surrogates, so he could have a large impact in affecting people’s perceptions and norms and in terms of who he puts in charge of various programs,” Salmon says. “The people who aren’t political appointees might be really resistant, but at the end of the day if the director of the CDC tells them to do something, unless it’s illegal, they’re probably going to have to do it.” For example, ACIP’s committee members, recommended by an internal steering committee, are ultimately appointed to four-year terms by the secretary of health and human services—who is appointed by the president. In addition, any decision made by ACIP can be rejected by the CDC chief, who is also appointed by the president and doesn’t require congressional approval. And the Vaccines for Children Program only covers vaccines officially recommended by the CDC.

Two additional powers the top executive has are forming presidential commissions and executive orders, Salmon says.

“Presidential commissions don’t carry the weight of law, but they’re really impactful,” Salmon says, noting that many recommendations from the 9/11 presidential commission were eventually implemented. In addition, “the power of the president to create change through executive orders seems to be increasing through time, so who knows what executive orders he might give.”

Like the bully pulpit, creating a commission could also send the wrong message, creating fear and confusion about settled science. ‘[W]e need a commission’ may make some families who [aren’t aware of the science] or have newly diagnosed children with autism think this is something we need to study, and … withhold vaccines from their children,” Singer says. “When you withhold vaccines, you do absolutely nothing to reduce your child’s chance of being diagnosed with autism. But you absolutely increase the chance that your child could contract a vaccine-preventable disease from which he or she could die.”