When celebrity and science collide, harmful side effects may occur.

The latest case happened last weekend when the Tribeca Film Festival pulled a documentary from its program by a discredited former doctor whose research into the connection between vaccines and autism has been debunked. After festival co-founder Robert De Niro initially defended the film's inclusion, Tribeca - facing an uproar from doctors and experts - pulled it.

The film, "Vaxxed: From Cover-Up to Catastrophe," is directed by Andrew Wakefield, a former British gastroenterologist who was stripped of his medical license in 2010. The British medical journal BMJ called Wakefield's study connecting autism and vaccines - which was retracted by the Lancet, a medical journal - an "elaborate fraud."

Scientific research has consistently found the MMR vaccine (given to children for measles, mumps and rubella) to be safe and have no link to autism. Cases of measles, however, have increased in recent years, largely infecting unvaccinated people.

De Niro acknowledged he personally chose to program the film at the festival, something he had never previously done. "My intent in screening this film was to provide an opportunity for conversation around an issue that is deeply personal to me and my family," said De Niro, who, with his wife, Grace Hightower De Niro, has an 18-year-old son with autism.

No one would question that the issue is personal to De Niro. But the Tribeca Film Festival, which opens its 15th edition on April 13, is an extremely public event. When news of the documentary's scheduled screening spread, disease experts were distressed that the festival would lend its megaphone to a film by a disgraced doctor. Michael Specter, the New Yorker staff writer and medical expert, called it "a disgrace" for the festival, and compared Wakefield's film to "Leni Riefenstahl making a movie about the Third Reich."

More on this...

The episode is only the latest instance of the medical community being forced to combat the influence of a celebrity promoting questionable science. It has particularly bedeviled questions over vaccinations, beginning with the anti-vaccination advocacy of TV personality Jenny McCarthy.

"Celebrities have had an out-of-proportion impact on the public's understanding of vaccine risk," says Arthur L. Caplan, head of the Division of Medical Ethics at New York University. "I don't want to overplay it; most people vaccinate. It's not like hordes of people are listening to Jenny McCarthy and saying, 'Forget the American Association of Pediatrics, I'm going with the former Playboy Bunny.'"

Jim Carrey and Rob Schneider have also spoken out against vaccines, as have some politicians. In a GOP debate last year, Donald Trump, while saying he supported them, added a story about a 2-year-old boy developing autism following vaccination.

Wakefield has vowed to press on with his film. He called the Tribeca Film Festival reversal "another example of the power of corporate interests censoring free speech, art, and truth."

Steven Silberman, author of "NeuroTribes: The Legacy of Autism and the Future of Neurodiversity," believes the claims of anti-vaccination campaigners are rooted in a misunderstanding of autism history. Autism isn't a historical aberration, he says, but has long been part of humanity - just less diagnosed.

"I have tremendous respect for Robert De Niro and tremendous compassion for his interest in prompting a conversation about his son's condition," says Silberman. "The problem is that if we're arguing about vaccines, we're having the wrong conversation. We should be talking about how we should give people like Robert De Niro's son a better future, one in which they can live more independently, have access to the support and resources they need, and have a chance to make a living."

Increasingly, doctors are fighting to seize the spotlight for health and medicine issues from celebrities, whose public platforms have far more reach than medical journals. Celebrities are also sought out to be spokespeople for new drugs, blurring their role. Since Milton Berle stumped in the 1950s for an antidepressant called Miltown, they've been prominent endorsers, from Jack Nicklaus for high blood pressure to Brooke Shields for thin eyelashes to Sally Field for osteoporosis.

Their influence can be considerable, sometimes for good. After Katie Couric's live on-air colonoscopy on the "Today" show in 2000, researchers recorded a nationwide increase in colonoscopies of more than 20 percent.

But often, the health advice of celebrities - well-meaning as it may be - could come with its own Surgeon General warning.

Reality star Kristin Cavallari (who has also spoken out against vaccines) recently caused a stir when she provided a homemade goat's milk baby formula recipe to People Magazine. The magazine listed it online under the section "Great Ideas" before removing it. (The American Academy of Pediatrics recommends breast feeding for an infant's first six months, and warns against the dangers of homemade formulas.)

"It's part of the general impact celebrities are having on health," says Caplan. "Gwyneth Paltrow is certainly emitting an unceasing stream of hot air about many health practices, from colonics to who knows what. It's a constant battle to try to correct misperceptions."

That battle, though, can come at a cost.

"As long as we're talking about Andrew Wakefield and 'Vaxxed,'" says Silberman, "we're not talking about giving autistic people and their families happier, healthier and safer lives."