Yesterday, President-elect Donald Trump met with Robert F. Kennedy Jr. — a man who believes in the debunked and fraudulent theory that vaccines cause autism. Trump also reportedly asked Kennedy to head a new “commission on vaccine safety and scientific integrity.” The purpose of this new commission isn’t exactly clear, but hours after the meeting a Trump spokeswoman said in a statement that the president-elect is “exploring the possibility of forming a commission on Autism.” That statement makes it seems that, once again, Trump is legitimizing a dangerous conspiracy theory that is already putting American lives at risk.  

Vaccines are key to preventing horrible, debilitating, and often fatal diseases that have been plaguing our society for centuries. Infectious diseases like measles, chickenpox, whooping cough, and smallpox brought over to the New World by European settlers killed likely millions of Native Americans. Just over a century ago, hundreds of thousands of people in the US became infected with measles, smallpox, diphtheria, and pertussis every year. Thousands of them died, often children. The development of vaccines changed all that.

But vaccines have come under attack by a group of people who completely disregard scientific evidence. One of these outspoken anti-vaxxers is Kennedy, who has promoted anti-vaccine propaganda in articles and a 2014 book he edited. Kennedy has claimed that thimerosal, a mercury-based additive in vaccines causes neurological disorders in children — a theory that’s been debunked. In 2015, at the presentation of an anti-vaccine movie in California, he said that vaccine-linked autism is a “holocaust.” And he’s lobbied Congress to exempt parents from state vaccination requirements. “RFK Jr. is someone who has no credibility, he has no medical or scientific credentials,” says Peter Jay Hotez, a vaccine researcher and president of the Sabin Vaccine Institute.

The anti-vaccine movement has resulted in more parents opting out of vaccinating their kids, and that has resulted in new outbreaks of highly infectious diseases like measles. “Infectious diseases in the history of humanity represent one of the most common causes of severe disease, disability, and mortality,” says Mark Schleiss, a pediatric infectious diseases specialist at the University of Minnesota. “The development of vaccines and implementation of vaccines is the single most important medical advance in the history of medicine.”

Between 2000 and 2015, the measles vaccine has saved the life of over 20 million children all over the world, according to the World Health Organization. The polio vaccine has saved over 600,000 lives per year and the hepatitis B vaccine over a million lives, according to 2003 research. A 2014 study published in Pediatrics found that vaccinating children prevents 20 million cases of disease every year in the US, by projecting from 2009 data. About 42,000 early deaths are also prevented, saving the country almost $70 billion annually. “Vaccines save lives,” says Peter Jay Hotez, a vaccine researcher and president of the Sabin Vaccine Institute. “The impact has been unquestionably huge.”

Some people, however, don’t seem to hear the message and decide to forgo vaccination, for themselves and their children. The anti-vaccine movement picked up at the end of the 1990s, after a now-discredited study by Andrew Wakefield suggested a link between vaccination and autism. In 2010, the prestigious journal that published the research, The Lancet, retracted the paper, and many studies have disproved Wakefield’s original report and showed that vaccines do not cause autism. Autism is a developmental disorder that is most probably genetic.

Unfortunately the science isn’t convincing some people. Celebrities like Jenny McCarthy have spread conspiracy theories about “toxins” in vaccines that can cause autism, and people from both sides of the political spectrum have voiced anti-vaccine beliefs: Green Party candidate Jill Stein and Libertarian Gary Johnson expressed mixed views over vaccines. And now, we have a president-elect who has also repeatedly questioned the safety of vaccines and vaccine policies, and has given voice to the unfounded anti-vaccine theories that have no basis in science.

“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,” Trump said during a Republican presidential debate last year. He also repeatedly tweeted about vaccines causing the developmental disorder.

The anti-vaccine movement has resulted in communities around the US — especially in California and Texas — where large shares of the population aren’t vaccinated. As a result, we’ve seen a comeback of totally preventable diseases that were once eradicated from the US. In 2015, a measles outbreak at a Disneyland in California resulted in more than 100 people across multiple states being infected. Texas is a ticking bomb waiting to happen, according to Hotez, who just published a paper in Plos Medicine about the state’s decreasing vaccination rates. In Texas, there are more than 40,000 children who were not vaccinated for nonmedical reasons, a 19-fold increase since 2003. For a highly infectious disease like measles, if vaccination rates drop below 95–90 percent, you’re likely to see outbreaks, Hotez says. “We’re already at the point when we should start seeing outbreaks of diseases,” he says.

Anti-vaxxers pose an incredible danger not only to themselves, but also to people who can’t be vaccinated because of medical conditions. People who have immune system disorders, or have weak immune systems due to transplants or because they have cancer, can’t be vaccinated. “They rely on us to get vaccinated so we don’t get them sick,” says Arthur Caplan, a bioethics professor at New York University Langone Medical Center. “Protecting the weak and the vulnerable is your first moral obligation as a society.”

And that’s what’s so troubling about President-elect Trump toying with the idea of creating a commission on vaccine safety, and even meeting with a vaccine denier. The science on vaccines is settled, the link with autism is a fable, and the leader of this country can’t legitimize unfounded conspiracy theories that will cost American children their lives. “What could be more morally repugnant than to engage in public policy and practice that would lead to lives being lost of American citizens,” says Schleiss, the University of Minnesota professor. “This should be a bipartisan issue, this should not be a political issue. This should really be about what’s best for our children and what’s best for our public health.”