From the perspective of presidential politics, the question of vaccine safety seems like the pseudoscientific issue that might never die.Though a connection between vaccines and autism has been debunked at the highest levels for at least six years, the issue keeps creeping into public debate.

Last week, Green Party nominee Jill Stein made headlines for equivocating on the safety of vaccines. “As a medical doctor, there was a time where I looked very closely at those issues, and not all those issues were completely resolved,” she told The Washington Post. “There were real questions that needed to be addressed. I think some of them at least have been addressed. I don’t know if all of them have been addressed.”

Multiple and well-publicized studies over the past two decades have found no connection between vaccinations and the development of autism. The only clinical research ever to make a connection—an infamous 1998 study—has since been widely debunked and retracted by The Lancet, after its author was found to have a mess of financial conflicts and to have falsified research data*.

“It was utterly clear, without any ambiguity at all, that the statements in the [1998] paper were utterly false,” said the Lancet editor who first published it, after a 2010 debunking. “I feel I was deceived.”

On Saturday, Colin Meloy, the singer and guitar of the Decemberists, tweeted at Stein, bluntly asking whether she believed vaccines cause autism. Stein clarified that “I’m not aware of evidence linking autism with vaccines.” Some Twitter users reported that she had first sent and then deleted an earlier tweet in response to Meloy, which more clearly stated that there was “no evidence” linking the two. In an email, Stein’s spokeswoman told me that “The deleted tweet was the result of a miscommunication among staffers.” She added that “Dr. Stein has repeatedly articulated her support for vaccination,” and accused the Washington Post piece of being “framed to cast doubt on that question.”

Stein tweeted again, saying “I support vaccinations,” on Monday.

But Stein is not the only candidate to address vaccines this election cycle. As first pointed out by the Twitter user @mcclure11, three of the four media-receiving presidential candidates have appeared to pander to anti-vaccine advocates. Libertarian Party nominee Gary Johnson has tweeted “No to mandatory vaccines.” And Donald Trump linked vaccines to autism in a GOP primary debate last fall, before being corrected on-stage by the surgeon Ben Carson.

Hillary Clinton tweeted in support of vaccines in February of this year. “The science is clear: The earth is round, the sky is blue, and #vaccineswork. Let’s protect all our kids,” she said.

This round of equivocation from candidates may seem ominous—but, if anything, questions from party leaders over the safety of vaccinations have lately decreased. Comments like these were more common eight years ago. In 2008, Clinton, Barack Obama, and John McCain seemed to question the safety of vaccines. “We’ve seen just a skyrocketing autism rate,” said Obama said at a campaign stop in Pennsylvania. “Some people are suspicious that it’s connected to the vaccines.”

“The science right now is inconclusive, but we have to research it. Part of the reason I think it’s very important to research it is those vaccines are also preventing huge numbers of deaths among children and preventing debilitating illnesses like polio,” he said.

Earlier that year, McCain had said there was “strong evidence that indicates that [a rise in autism rates] has got to do with a preservative in vaccines.”

But as president, Obama has spoken clearly about the safety of vaccines. “The science is pretty indisputable,” he said last year. “There is every reason to get vaccinated — there aren’t reasons to not.”

In other words, popular and scientific consensus have moved closer together over the past decade. What's more, experts no longer think there's been a sudden rise in autism cases; rather, they see rising diagnosis rates as due to increased understanding and changing social norms.

Surveys also reveal that the vast majority of Americans correctly understand vaccines to be safe. There simply aren’t many votes to win by pandering to anti-vaxers. In a society of millions, though, the margins are large enough to drive thousands of votes—and maybe that’s why some candidates continue to take less-than-firm stances on the safety of vaccines.

Dan Kahan, a professor at Yale who has studied public perception of science, told me that no matter how you phrase the question, more than 75 percent of Americans always endorse the safety of vaccines when polled. That support holds across many disparate political groups, including Tea Party supporters and liberal Democrats.

“Because the attitudes about vaccines are pretty much uniform across the political spectrum, it doesn’t seem like a great idea for any candidate to be anti-vaccine,” he said. “The modal view is leave the freaking system alone.”

That’s an important public health asset, he said, and one not to be trifled with. And since public-health consensus has only gotten clearer on this issue during Obama’s two terms, maybe this is the last election we’ll hear about vaccines as a campaign issue. The American people know what’s what—it’s time for our political leaders to make it clear they do too.


* This article originally stated that Andrew Wakefield’s study was conducted poorly. The BMJ reports that the study was conducted not just poorly, but fraudulently, with significant misreporting of the data produced by the small sample size. We regret the error.