But correlation is NOT causation. Just because they occur around the same time frame doesn't mean one caused the other.
Anti-vaccination crusaders have a hard time understanding this. People like actor Jim Carrey are sold on the notion that vaccines cause autism.
Recently, Carrey issued a Twitter tirade to his millions of followers that included misinformation, misused photographs and misfired ad hominem attacks. He even labeled California Gov. Jerry Brown a "corporate fascist
" and a shill for big pharma.
Carrey isn't alone in his anger. Thousands of parents lobbied and protested the California State Assembly in the lead-up to its historic vote passing Senate Bill 277, which mandates vaccination for all of California's schoolchildren without exemptions for religion or personal belief. Only children whose doctors certify a medical basis for skipping immunization (such as an immune system deficiency) or children who are home-schooled or otherwise studying independently, will get exemptions.
Throughout the legislative debate it wasn't known what the governor would actually do when the bill reached his desk. Just three years ago, Brown inserted an additional loophole for religious beliefs in a bill that added a requirement of physician counseling for parents seeking a personal belief exemption.
But Gov. Brown signed Senate Bill 277
, making California just the third state to dump personal and religious vaccination exemptions. Carrey got busy on Twitter that evening.
Scientific understanding neither requires nor ever achieves total consensus. The existence of manmade climate change is no longer a serious debate in the scientific community, for example, but we'll never see all scientists agree with the theory. Heck, only 4 out of 5 dentists can agree on the value of sugarless gum.
The underlying science behind the vaccine safety is the same in 2015 as it was in 2012. The science is based on huge studies that compare autism rates in otherwise similar populations of vaccinated versus unvaccinated children. One of the largest studies, published in the New England Journal of Medicine
back in 2002, compared 440,655 children who got the MMR vaccine to 96,648 who didn't get the jab.
This is the kind of expensive, meticulous science required to investigate the otherwise frightening correlation between giving a child a vaccine and that same child later demonstrating symptoms of autism. The studies concluded that there is no link between autism and vaccination.
But some people, either because of lack of knowledge or exposure to misinformation, became opposed to vaccination. So they stop vaccinating their children. The result? We've seen the reemergence of measles in various states, especially California.
Measles is a deadly disease that we thought we'd eliminated from domestic transmission back in 2000, but now it's come back with a vengeance, starting with December 2014 exposures in Disneyland that ultimately led to a total of 131 cases
. We've now proven that the outbreak spread like wildfire precisely because of California's low vaccination rate. Meanwhile the United States just recorded its first measles death in 12 years
By signing a responsible new law, Gov. Brown has proven yet again that he's the best kind of politician: one who evolves his policies as the evidence demands.
The Golden State is dotted with schools where the vaccination rate can dip to 50% or lower
. The only problem with the new California law is that it won't go in effect until next summer. Given the catchup period once it goes into effect, California's still a sitting duck for another, worse outbreak.
It's in this climate that Jim Carrey is doing his best to spread his conspiracy theories and fears. And he won't stop. Carrey claims he's not anti-vaccine, he just wants safe vaccines. Both he and Robert F. Kennedy Jr., who's also anti-vaccine, are hung up on thimerosal, a preservative that contains the element mercury, which can be toxic depending on its chemical state. Fortunately, the mercury compound used in some vaccines, like the flu shot, isn't toxic
in the trace amounts needed for vaccines.
Thimerosal used to be in some childhood vaccines, but companies removed it due in part to the hysteria sparked by a fraudulent scientific publication
. But even a large-scale analysis comparing children who got thimerosal-containing vaccines to those who got the same vaccines without thimerosal prove there's no link between thimerosal and autism.
All medicine is pragmatic. It's the best we can do right now. Carrey and Kennedy don't seem to understand that this is how medicine works.
I hope one day we'll have vaccines that we can give far outside of the window of time when autism typically emerges, putting this worrisome temporal correlation out of everyone's mind once and for all.
But for now, let's take it from a doctor, not an actor: Everyone should vaccinate their children not only for their sake, but for all the sick kids who can't get vaccinated.
As for Jim Carrey -- please keep your medical misinformation to yourself.
Correction: An earlier version of this essay incorrectly stated that thimerosal was once in the MMR vaccine. It was not
, according to Centers for Disease Control and Prevention.