Vaccine Reality Check: A Tiny Risk of a Tiny Risk
It’s easy to assume from reading the news that scientists have reflexively pooh-poohed concerns about a vaccine-autism link. Here’s the BBC: “Medical experts have overwhelmingly rejected any link between vaccines and autism, warning that promoting such a theory endangers public health.” The Wall Street Journal said that the preservative thimerosal was “wrongly accused of causing autism.” This glosses over an important sequence of events. Scientists didn’t reject the idea out of hand, when the theory was first floated. They conducted a mountain of research, and then the wrongness of the theory became clear.
This old accusation about vaccines is back in the news because of President-elect Donald Trump’s tweets claiming that children became autistic after receiving “massive shots.” He is said to have discussed vaccine safety not with any scientists but with Robert F. Kennedy Jr., a lawyer who has written books arguing for a link between autism and thimerosal, which is used in some vaccines.
Some news accounts dismissed these concerns by stating that there’s no evidence for a link between childhood vaccines and autism. But parents want more than just absence of evidence; they rightly expect evidence of absence. That’s accepted public policy. Even if there’s no evidence of danger, new drugs can’t be unleashed on the public until they pass a series of safety studies.
Childhood vaccines have undergone dozens of studies on four continents conducted by hundreds of researchers. That’s yielded evidence that the potential risk of autism is so small that it’s dwarfed by the risk of the diseases the vaccines protect against. The diseases may be mild in some cases, but not always. There’s a measurable risk of permanent brain damage from measles, for example.
The saga of vaccine fears is compounded by the erroneous idea that scientists should be able to prove that vaccines are safe. What is "prove"? What is "safe"? Science deals in probabilities. The best that we can hope for is what we have: reasonable certainty that these drugs are reasonably safe.
People on both sides are spreading confusion, said UCLA epidemiologist and statistician Sander Greenland. Those who oppose vaccines by demanding absolute proof of safety are asking more than science can deliver. They should take a philosophy class on epistemology. And scientists who claim they’ve proven vaccines safe are expressing overconfidence. They should join the class. As Greenland said, “the only thing science can do is establish a margin of safety.”
Science can offer risk-benefit ratios. And here, the bottom line is that any potential risks in taking the vaccines are much smaller than those posed by skipping them, said Stanford epidemiology professor Steven Goodman. There are some documented risks, which are rare, and then there’s autism, which is probably a non-risk, or at worst a very unlikely one. Think of it as a small risk of incurring a small risk: Science can’t absolutely rule out the autism link, but it can show that the risk, if there is one, is much lower than that the risk of death or brain damage posed by remaining vulnerable to measles, pertussis and other preventable diseases.
Goodman has served on an Institute of Medicine panel examining vaccine risks, as well as another panel on drug safety. The vaccine panel, which met from 2001 to 2004, took autism concerns so seriously, he said, that they produced nine reports to address different hypotheses. Those included the notion that the preservative caused harm, which has been raised by Kennedy, and the fear Trump has expressed in his tweets -- that doctors might be putting kids at risk by giving them too many vaccines at once. The reports all concluded that vaccines can’t be more than a very small risk factor.
Goodman said he’s met with activist parents who were worried their autistic kids were harmed by vaccines, and was impressed with how much they knew about science. The problem, he said, is that many hold a very narrow view of what science entails. To them, science included only laboratory tests that could give specific information on individual kids. The science of studying large populations … well, he calls it epidemiology, but they call it junk science.
The term "junk science" is so ill-defined that it can be invoked to dismiss anything people happen to disagree with. Still, he said he’s sympathetic to the fact that science can’t explain why their kids developed autism. Before anyone raised suspicion of vaccines, some researchers promoted another wrong and pernicious idea known as the “refrigerator mother” theory, blaming women for working or just not being attentive enough.
Recent work in genetics has tied some cases of autism to combinations of common genes, and others to “de novo” mutations that can occur in eggs or sperm and are therefore not carried by the parents. But genes don’t offer a full explanation, and scientists haven’t ruled out the possibility that genes make some people more vulnerable than others to environmental triggers.
No potential trigger has been explored as thoroughly as vaccines. It would be nice if scientists could give us proof that they are 100 percent safe, but that’s not realistic. In discussing the trouble with proof, physicist Richard Feynman once explained that he couldn’t prove that there were no flying saucers; he could only argue that they were very unlikely. Scientists took vaccine safety seriously. They found that an autism risk is extremely unlikely. Now it’s time for Kennedy and Trump to take science seriously.
This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.
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