In a series of recent tweets, actor Jim Carrey raged against a new California law banning the personal belief exemption for childhood vaccines. The bill, signed by Gov. Jerry Brown (D) on Tuesday, makes the shots mandatory for every child before attending public or private school. The only children who will be exempt from vaccines are those who have a medical reason to postpone them, such as an immune deficiency or cancer.
Carrey maintains that his objection is to the additives in vaccines, like thimerosal and mercury, not the vaccines themselves. "I am not anti-vaccine," he tweeted.
But it’s simply not possible to hold both beliefs, said Dr. Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia. Carrey’s insistence on making an issue out of a non-issue like the supposed dangers of the preservative thimerosal actually is an anti-vaccine position, Offit explained. By Offit's count, there are several high-quality studies that show thimerosal in vaccines does not cause autism or developmental delays in the children who receive them.
“What makes Jim Carrey anti-vaccine is that he takes a non-issue and he makes it an issue,” said Offit. "He puts out misinformation about vaccines, and therefore he’s anti-vaccine.”
Some vaccines, including certain flu vaccines, still contain trace amounts of thimerosal. Carrey likened this chemical to the methylmercury found in fish, which is a neurotoxin and can cause serious damage to people if ingested in large amounts.
But methylmercury and the ethylmercury used to preserve vaccines are two very different things, explained Offit. For one, everyone is exposed to methylmercury. It builds up in the body over a lifetime of exposure, and too much of it can cause nervous damage and permanent disability. Ethylmercury, on the other hand, is a byproduct the human body makes when processing thimerosal. It does not remain in the body for long amounts of time.
Ironically, thimerosal was first added to vaccines in the 1930s to make the shots safer. Repeatedly puncturing a vial that contained multiple doses of a vaccine carried the possibility of introducing bacteria, fungi and other contaminants into the container. Children who received the ninth or tenth dose from that vial were at higher risk of coming down with life-threatening infections than those who got the first or second shots from it, Offit said. But a now-debunked 1998 study on the link between vaccines and brain damage, as well as growing concern from a small number of parents suspicious of vaccine ingredients, set the stage for its removal, even though there was no scientific evidence that thimerosal was harmful.
In reaction to parental outrage over mercury in vaccines, the Centers for Disease Control and Prevention announced in 2000 that they were removing the chemical in most childhood vaccines -- a move that Offit, who served on the Advisory Committee for Immunization Practices at the time, voted against. In caving to unscientific fears about thimerosal, said Offit, the CDC’s decision to remove the additive may have actually alarmed parents more -- not reassured them -- when it came to vaccination safety.
"I think they unnecessarily scared the American public about thimerosal,” said Offit. “They caved to the perception that mercury just doesn’t sound good, instead of trying to educate the public that the quantity of mercury you’re being exposed to in a vaccine is infinitely less than anything that you’re exposed to elsewhere.”
The decision also gave a sheen of scientific legitimacy to anti-vaccination groups who took the decision to remove thimerosal as an admission of guilt. Sticking to the science, he says, will always be key when it comes to increasing vaccination rates.
“Frankly, who is Jim Carrey to comment on the science?” Offit said. "He’s an actor. Does he know the science? I don’t think so."