Vaccines don’t cause autism. But a tiny, tenacious group of anti-vaccine advocates really, desperately, hopelessly want them to.

That’s what led to a media frenzy this past weekend when it surfaced that Robert DeNiro, cofounder of the Tribeca Film Festival, explicitly requested that the festival include an anti-vaccine documentary produced by Andrew Wakefield, the disgraced gastroenterologist who was stripped of his medical license after publishing a now-retracted study attempting to connect the MMR vaccine to autism. The documentary dredged up the mythical association between autism and vaccines, with the added twist of claiming that the US Centers for Disease Control covered it up.

The anti-vaccine movement is as old as vaccines themselves.

The media responded by unanimously decrying the move and reiterating how many times that fear has been debunked. DeNiro then reversed course, yanking the film from the screening line-up. Predictably, cries of censorship rose up from the anti-vaccine camp. But like it or not, what happened at Tribeca isn’t censorship, says Karen Ernst, executive director of Voices for Vaccines, a parent-led, pro-vaccine advocacy group.

“My own theory is that DeNiro agreed to include this film and then screened it and realized it wasn’t very good and not worth including,” Ernst says. “I think it was a fair decision and that Tribeca Film Festival gets to pull a film that isn’t up to the quality they expect. The film still exists and can be seen by others.”

Of course, whether anyone really cares about seeing it is another question. The anti-vaccine movement is as old as vaccines themselves. Its earliest supporters believed Edward Jenner’s smallpox vaccine, made from cowpox, would turn people into cows. The myth that vaccines are bad for you has persisted despite centuries of scientific advancements, and long after smallpox itself was eradicated thanks to the first vaccine.

“Edward Jenner probably thought once people started to see that people aren’t turning into cows, that fears about vaccines would go away,” Ernst said. “We’ve certainly moved past the question of whether vaccines turns us into cows, but what the anti-vaccine movement doesn’t realize is that we’ve also answered the question of autism and vaccines.”

The baffling longevity of the movement speaks to its remarkable malleability.

The baffling longevity of the movement speaks to its remarkable malleability. Anti-vaccine advocates have moved the goalposts each time that science showed their most recent pet theory was bunk.

Today’s version of the movement began in the 1980s with a documentary calling attention to concerns about the diphtheria-pertussis-tetanus (DPT) vaccine and the publication of a book by Barbara Loe Fisher, the founder and director of today’s largest anti-vaccine organization in the US. Then Wakefield published his 12-child case series in medical journal The Lancet in 1998, sparking fears of a link between autism and the MMR vaccines in the UK. Within two years, the autism-MMR fears had crossed the Atlantic.

Gradually, however, studies debunked the MMR-autism fear. That was just in time for a new culprit to add fuel to anti-vaccine advocates’ fires: thimerosal. This ethylmercury-containing preservative had been used to prevent contamination in childhood vaccines until the CDC, citing too little evidence about its safety, decided to remove it “in a precipitous and frightening manner,” said Paul Offit, MD, chief of the division of infectious diseases at Children’s Hospital of Philadelphia.

Despite the CDC’s ominous decision, there remains no known risk from thimerosal’s use, something proven by years of subsequent research. Undeterred, anti-vaccine advocates pivoted again, now arguing that the real problem is children are receiving too many vaccines too early in life.

“It’s a game of Whack-a-Mole. Oh, did we say MMR? We meant thimerosal. Did we say thimerosal? We meant it’s too many too soon.”

“It’s a game of Whack-a-Mole,” Offit said. “Oh, did we say MMR? We meant thimerosal. Did we say thimerosal? We meant it’s too many too soon.”

Despite their best efforts, it’s practically impossible for researchers to keep up with ever-evolving fears. Ernst agreed that the parade of ailments pinned to vaccines may never end.

“Children get vaccines and children have health issues, and sometimes those things happen at the same time,” Ernst said. “As long as that happens, some parents are going to look to vaccines as the culprit.”

Admittedly, the CDC’s recommended immunization schedule has become more burdensome over the past two decades, Offit said, so it’s not irrational for parents to have concerns. The problem is that science can only move so quickly to address those concerns. Meanwhile, the clinical trial results showing that vaccines remain safe are unable to quell every parent’s worries.

“Each time you come up with a new hypothesis, it takes a long time to do the studies to test it,” said Daniel Salmon, PhD, deputy director of the Institute for Vaccine Safety at Johns Hopkins Bloomberg School of Public Health. “I could come up with 20 questions and you could spend the next 50 years trying to answer them.”

And even then, a small percentage of people will never accept what the evidence eventually reveals.

“We keep doing the research over and over with different questions, and the answer keeps coming back the same.”

“We keep doing the research over and over with different questions, and the answer keeps coming back the same,” Ernst said of the autism-vaccines concern. That’s why the media didn’t bite on the documentary—this wasn’t about censorship, it was about redundancy. “It wasn’t salacious because it was a tired old story, like the media reporting on the earth being round. By now, the general public knows the research has been done, and the media knows how to respond.”

But that doesn’t mean the issue will go away—or that concerns about vaccines ever will. But that doesn’t mean we should ever ignore questions as they arise. Salmon argues the opposite: That researchers should be investigating the public’s concerns thoroughly and speedily. In fact, he says that we need to dramatically increase funding for post-licensure vaccine safety research to five or 10 times what is being spent now.

“I don’t say that because there’s some large safety problem looming but because there are questions out there that are biologically possible that people are worried about and we should explore them,” Salmon said. “Society benefits so tremendously from vaccines that spending ten times more money in post-licensure vaccine safety research is a drop in the bucket. If you see a public concern bubbling up among people, let’s do the studies, let’s answer the question and show people we are being responsive to their concerns.”

And what are the next concerns likely to be? Salmon suggested two different possibilities. A vaccine ingredient could stir up anxiety if it gets connected to another health issue, as happened with thimerosal and legitimate concerns about mercury exposure. Or a new condition could be identified that happens to fit many of the symptoms that anti-vaccine advocates flag as suspicious.

“If you see a public concern bubbling up among people, let’s do the studies, let’s answer the question.”

The latter condition would likely be one affecting infants or children and that is growing in diagnoses (or appears to be). It should also have an unknown or complex cause, such as an interaction between unknown environmental exposures and genetics. People will start searching for possible exposures, and vaccines will top the list.

“Put those together, and vaccines are the perfect culprit,” Salmon said. “If we went back 20 years, I think autism could have been predicted [as an anti-vaccine target] because it had all those characteristics.”

That means anti-vaccine advocates aren’t going away, and they’ll keep looking for ways to get their message out. Tribeca may prove to be the beginning of a new trend.

“The anti-vaccine movement has lost on the science front, they’ve lost on the media front, and they’re beginning to lose on the political front,” Ernst said. “The next front they’re looking to is the documentary front. They’re very interested in making their own media to frighten people away from vaccinating their children, and I anticipate they will try a number of documentary films in the coming years.”

And long after they’ve left the playing field, anti-vaccine advocates will keep shifting those goalposts.

“It is never-ending, and it’s sort of never-ending by necessity because the anti-vaccine movement is based on some really strong and really emotional beliefs,” Ernst said. “In order to sustain itself, it has to keep reinventing its stories.”