Actor Robert De Niro is the latest celebrity to say he thinks vaccines might cause autism. But decades of study have shown no link at all, and scientists are becoming increasingly impatient with the refusal to accept their findings.
De Niro said Wednesday he now regrets pulling a controversial film called "Vaxxed: From Cover-Up to Conspiracy" from the Tribeca film Festival.
"If you are scientists, let's see, let's hear," De Niro told TODAY. De Niro says his 18-year-old son has autism and while the actor did not directly say he fears vaccination caused his son's condition, he said he wonders about it.
But scientists have debunked, often multiple times, every assertion that De Niro makes. They've been made and knocked down many times in the past 20 years as a small but highly vocal group of vaccine critics raise them.
"It's been answered again and again and again," says Dr. Paul Offit, a pediatrician at Children's Hospital of Philadelphia who has written broadly on the vaccine doubters. "It just saddens me that Robert De Niro doesn't believe those excellent studies."
Here are the answers to the points De Niro raised.
"I am not anti-vaccine. I want safe vaccines."
Vaccines are among the safest medical interventions known, doctors say. These experts include government doctors from the Centers for Disease Control and Prevention, the Food and Drug Administration and the National Institutes of Health. They include independent academic scientists from universities, the American Academy of Pediatrics and medical centers that are not affiliated with either the federal government or the pharmaceutical companies.
While no drug or treatment is 100 percent safe, they say vaccines are far, far safer than the diseases they prevent.
"Robert De Niro wants what we all want, which is the safest possible vaccines, and vaccines are held to the highest standard of safety," Offit said.
"They're tested in tens of thousands of children before they're sent to the Food and Drug Administration for licensure and then they're tested in millions of children post-licensure to make sure that they are as safe as possible."
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The World Health Organization estimates that measles vaccines save 1 million lives a year. In contrast, just 57 claims of deaths due to measles vaccines have been filed through the U.S. Vaccine Injury Compensation Program, a no-fault system set up to compensate people injured by vaccines. The program doesn't say how many of those claims were actually allowed.
A special federal court, the U.S. Court of Federal Claims, ruled against three families in 2009 who claimed vaccines caused their children's autism, saying they had been "misled by physicians who are guilty … of gross medical misjudgment."
"There is not a year that goes by at Children's Hospital of Philadelphia where we do not see a child die from a vaccine preventable disease, typically influenza," Offit said. "Less commonly it's pneumococcal, occasionally it's pertussis or whooping cough."
De Niro asked for more research into the possible harms of vaccines.
"To shut it down, there's no reason to. If you are scientists, let's see, let's hear."
Scores of studies have been done to address these questions, even over the objections of doctors who say the questions have been asked and answered. Most examined is the question of whether vaccines might cause autism.
The independent Institute of Medicine looked at the question so many times that it issued a final report in 2001 saying these studies were using money that could be better spent elsewhere to find the causes of autism, and then another in 2005 saying there really, really is no link between vaccines and autism but said doctors and public health experts were doing a poor job of explaining this to people.
Related: Don't Call Vaccine Doubters Dumb
These include studies looking at a mercury-based preservative called thimerosal, which keeps dangerous bacteria and fungi from growing in vials of vaccines.
"There is a link and they say there isn't. The obvious one is thimerosal which is a mercury based preservative. I am not a scientist. But I know. Let's just find out the truth," De Niro said.
Researchers have been unable to find evidence thimerosal in vaccines can damage human brains, but drugmakers took it out of all childhood vaccines anyway years ago because of the fears.
And vaccine makers have changed vaccine formulations over the years to mollify other worries. The whooping cough vaccine was reformulated in the 1990s because of side effects that included pain and swelling from the shot and fever. But there's some evidence the newer vaccines doesn't protect as well and that recent outbreaks of whooping cough may be the result of reformulating the vaccines.
De Niro also asks whether some kids might really have a special sensitivity to vaccines.
"How the vaccines are dangerous ..for certain people who are more susceptible. Nobody seems to want to address that."
Again, it has been examined.
Dr. Anjali Jain of The Lewin Group, a health consulting group in Falls Church, Virginia, compared kids who hadn't been vaccinated because of a family history of autism to kids who had gotten their shots.
They found the risk of autism was less than one percent in vaccinated kids, whether they had an older sibling with autism or not.
Other researchers have answered questions about whether kids get too many vaccines at once— they don't.
Lawmakers have begun cracking down on parents who want to choose, saying these choices endanger not only the children not being vaccinated properly, but others in the community.
Autism spectrum disorder refers to a large range of conditions, from the relatively mild symptoms of Asperger's to severe and profound intellectual deficits and an inability to communicate with others. Symptoms often overlap with other disorders such as attention deficit/hyperactivity disorder, cerebral palsy or various learning disorders.
The Centers for Disease Control and Prevention has been studying how common autism is for years now. It's found it is a distressingly common diagnosis with somewhere between 1 in 45 and 1 in 68 kids having the condition.
Research into the effects of Zika virus infection is clearly showing that particular virus can get into a developing baby's brain and damage it.
"There is no debate," Offit says.