Donald Trump has soared to the top of polls for the Republican nomination for president, and many have said it was because he makes bold statements and “speaks truth” to voters. But during last night’s presidential debate, Trump used his high-profile position to repeat one of the most dangerous health myths floating around the internet: that vaccines cause autism.

The study behind this myth has been widely discredited and retracted. Dozens of subsequent studies have examined the vaccine and autism link and concluded there is no link. Earlier this year, a study published in the Journal of the American Medical Association observed more than 95,000 children and found that the measles, mumps, and rubella (MMR) vaccine does not increase the risk of autism. You can learn more facts about vaccinations with our primer, “5 Things to Know About Vaccinations” here.

Despite zero research supporting this vaccine-autism link, it’s incredibly difficult to convince some parents vaccinations are safe. Trump’s debate performance illustrated why: a personal anecdote of a child who was vaccinated and then developed autism (even in the absence of any proof showing it was the vaccinations that caused autism) is more powerful and connects with parents more than reams of scientific literature.

In response, we offer to Donald Trump the cases of children who contracted measles—a vaccine preventable disease—in California earlier this year. According to the World Health Organization, 1.5 million children under the age of 5 died from vaccine-preventable diseases in 2008, and vaccines prevent 2-3 million deaths every year.

If Donald Trump were our doctor, we’d have one thing to say to him: “you’re fired!”