Medical Examiner

Zealots Like RFK Jr. Have Already Made Vaccines Less Safe

Not just because they fuel anti-vaxxers. This type of paranoia impedes our ability to accurately consider evidence. 

vaccine vial.
Whether or not it contains thimerosal, this vaccine is perfectly safe.


Robert F. Kennedy Jr., political scion–turned–anti-vaccine alarmist, emerged from a meeting with President-elect Donald Trump on Tuesday claiming that Trump had offered him a position leading a vaccine safety commission. This is a terrible idea for reasons that should be apparent, and a dangerous idea, because Kennedy’s anti-scientific rantings have already exerted a chilling effect on honest medical discourse for at least a decade. The thimerosal episode is a perfect example.

In the early 20th century, manufacturers sold all vaccines in multidose vials from which doctors and nurses would draw single doses. The problem was that this required a needle to go in and out of the vials, and bacteria and fungi can ride those needles into the vials. Contaminated vaccines killed children in the 1920s.

Enter thimerosal. When added to vaccines, the chemical prevented contamination without undermining vaccine efficacy. It saved lives.

There was just one problem: Thimerosal contains mercury. This became an issue in the 1990s when studies emerged from the Faroe Islands showing that children chronically exposed to mercury from eating fish and whale blubber suffered neurodevelopmental delays. Even though every one of us necessarily consumes some amount of mercury every day, the public became extremely concerned about the chemical. A congressman from New Jersey directed the Food and Drug Administration to hunt down all sources of introduced mercury in medications, which spurred the public realization that vaccines contain mercury.

Dr. Neal Halsey, one of the doctors responsible for overseeing the vaccine schedule at the time, was worried.

“My first concern was that it would harm the credibility of the immunization program,” he later told the New York Times. “But gradually it came home to me that maybe there was some real risk to the children.”

Behind closed doors, a legitimate scientific and policy debate ensued. Mercury is a neurotoxin, but the dosage, timing, and chemical form of mercury in thimerosal were completely different from what Faroese children experienced.

“Infants are exposed to more mercury from breastfeeding than they’d ever get from vaccines,” says Paul Offit, chief of the division of infectious diseases and director of vaccine education at the Children’s Hospital of Philadelphia. “It’s in the earth. It’s in the water we drink. If you want to achieve zero tolerance for mercury exposure, you’d have to move to another planet.”

At the time, there was no evidence that the thimerosal in vaccines caused harm. There was also not enough evidence that thimerosal did not cause harm, though. So, the Centers for Disease Control and Prevention and the American Academy of Pediatrics erred on the side of caution. They asked vaccine manufacturers to remove thimerosal from vaccines. Today, only a small portion of influenza vaccine contains the preservative.

During the transition, public health authorities tied themselves in knots trying to tell parents they were removing thimerosal from vaccines while simultaneously reassuring them that thimerosal was completely safe. “The current levels of thimerosal will not hurt children,” the AAP said, “but reducing those levels will make safe vaccines even safer.”

We now know that thimerosal-containing vaccines are not harmful to children. They never were. Subsequent studies have shown that the form of mercury in thimerosal passes through the body more quickly than the form found in fish and is much less likely to be absorbed. There have been seven well-constructed studies confirming the safety of thimerosal-containing vaccines. (See here, here, here, here, here, here, and here, and I’m sure I’m missing some.)

The other thing we now know? It turns out that eliminating thimerosal—at least in the manner public health authorities did—carried its own risks. In the immediate aftermath of the order to remove thimerosal from vaccines, some health care providers got spooked and delayed vaccine administration, needlessly putting infants at risk of vaccine-preventable diseases. At least one died from hepatitis B.

And we know that the fear of mercury the switch created convinced some desperate parents of autistic children, already confused about the cause of their children’s condition, to inject their kids with chemicals intended to rid their systems of mercury. This was unnecessary. And one of them died.

Eighteen years later, doctors still argue over the decision to remove thimerosal from vaccines. Halsey has staunch defenders who describe him as an egoless man who was trying to put child safety first, making a very difficult decision in a politically charged environment without the data he needed. Others still rue the decision, arguing that even though there wasn’t hard evidence, our scientific understanding of and experience with thimerosal justified keeping it while research continued.

“We caved to public perception,” Offit says. “You’re always better off trying to explain the science—you owe the public that. We made a mistake.”

Wherever you come down on the decision, the real villains in the thimerosal episode are vultures like Robert F. Kennedy Jr., who seized on the scientific uncertainty and the public communications challenges to scare the hell out of people.

Kennedy was not in the room with the scientists tasked with protecting children—he never had to make those difficult decisions. He came onto the scene after the fact, shouting about a conspiracy and claiming that the government had buried data showing that thimerosal was dangerous. His only evidence is private conversations with scientists who uniformly deny holding the views Kennedy attributes to them.

Specifically, Kennedy insists that thimerosal causes autism. But there has never been any reason to believe that thimerosal or any form of mercury causes autism. No credible scientist ever believed that. The studies in the Faroe Islands were unrelated to autism. Even in mass mercury exposures, such as the 1971 Iraq grain poisoning, there is no spike in autism. Kennedy merely exploited an uncertainty in the science to pursue his own agenda.

There are real harms to Kennedy’s rantings. His ongoing attack on the CDC—which he continues to villainize—has forced the government to keep funding studies to disprove his crackpot theories when we could be devoting that money to cancer or malaria research, or even studies on the safety of new vaccines coming onto the market. Kennedy’s public scare tactics also prevent honest researchers from speaking openly about gaps in the data, because they know Kennedy will mischaracterize all requests for more data as evidence of a government conspiracy to kill your children. Giving him an official position will force honest scientific debate further into the shadows—exactly the situation Kennedy claims to be fighting.

When it comes to his views on vaccine safety, Robert F. Kennedy, Jr. is dishonest, uninformed, insane, or some combination of them. His refusal to accept medical evidence has put children at risk, and giving him an official position will … you know what? It’s so obvious, it’s not even worth writing. It also doesn’t matter. Neither Trump nor Kennedy care about facts.