Not Up for Debate: The Science Behind Vaccination

The following originally appeared on The Upshot (copyright 2015, The New York Times Company).

Whenever I sit down to watch a presidential debate, I have one sincere hope: that vaccines won’t come up at all. Besides the fact that there really is no “debate” when it comes to the science of how they work or how they may harm, merely talking in public about denying vaccinesoften leads to the solidifying of people’s views.

My hopes were dashed as Wednesday night’s debate wound down, though. Questions about vaccines and autism were asked not only of Donald Trump, but also of the two physicians taking part: Ben Carson, a neurosurgeon, and Rand Paul, an ophthalmologist. The doctors, at least, should know better.

Here are the facts:

Vaccines aren’t linked to autism.

The number of vaccines children receive is not more concerning than it used to be.

Delaying their administration provides no benefit, while leaving children at risk.

All the childhood vaccines are important.

There is simply no scientific evidence that links vaccines to autism. Many, many, many studies have confirmed this. The most recent Cochrane systematic review of research on the MMR vaccine included six self-controlled case series studies, two ecological studies, one case crossover trial, five time series trials, 17 case-control studies, 27 cohort studies and five randomized controlled trials. More than 15 million children took part in this research. No one could find evidence that vaccines are associated with autism.

This topic yields more evidence than any other I’ve ever written about in The Upshot. And this is one of the most studied subjects ever.

Nevertheless, some people keep calling for more research. Never mind that even a statistically significant link found at this point would almost have to be a false positive, given the millions of children already studied. That doesn’t prevent us from continuing to investigate this topic. This year, astudy was published in the Journal of the American Medical Associationthat looked at a cohort of about 100,000 children. All of them were followed from birth until they were 5 years old. Researchers once again looked at whether the MMR vaccine was associated with autism, and found that it was not. It wasn’t even found among children who had siblings with autism and who would therefore be at higher risk for the condition.

In fact, one of the few “studies” to find a link is still the original Lancet study, published by Wakefield et al. It was a glorified case series of a handful of children with autism. There were no statistics to prove a link. The study was later disavowed by nearly all the other authors, then retracted by the journal in 2004. In 2011, Brian Deer wrote a damning article laying out how almost all of the data were falsified in some way. The editors of the medical journal BMJ called the Wakefield study linking vaccinations to autism a “fraud.

That’s the evidence linking autism to vaccines.

It’s also not correct to call autism an “epidemic,” as Mr. Trump often seems to do. Autism is more prevalent as a diagnosis than it used to be. But much of that in recent years is because we’ve changed the definition of what it means to have “autism spectrum disorder.” For instance, 10 years ago, two-thirds of children diagnosed with autism had below-average intelligence.But today only about a third of those diagnosed with A.S.D. do. The fastest-growing group of children with autism have average or above average intelligence. We’re being more inclusive in the diagnosis.

I am in no way minimizing the challenges facing those who have autism, or denying its prevalence. I hope my recent column discussing whether we should universally screen for autism in small children persuades you that I take A.S.D. seriously. Scaring people by claiming that autism is spreading like a disease worries them needlessly, however.

Mr. Carson, though observing there was no evidence linking vaccines to autism, also said that many pediatricians were recognizing that “we are probably giving way too many in too short a period of time.” I know of no data that supports this assertion. Pediatricians, as a group, overwhelmingly support vaccines and the current vaccine schedule.

Vaccines do not stress the human body that much. Children are continuously exposed to foreign substances that activate their immune systems. In a manuscript published in Pediatrics in 2002, Dr. Paul Offit and colleagues estimated that infants could respond to about 10,000 vaccines at any one time. The ones we give could never “use up” the immune system. It is thought that 11 vaccines at once might require the attention of about 0.1 percent of the immune system.

Moreover, it’s not the number of shots or even the number of vaccines that we should be concerned about. We should be talking about the number of antigens in the vaccines. Antigens are the molecules that spark the immune system into action. Vaccines are made to trick the immune system into developing weapons against certain antigens that are similar to the disease before having to face the disease itself.

Over time, researchers have been able to purify vaccines so that they contain fewer antigens, while still conferring immunity. They get the same results while asking less of the immune system. A single smallpox vaccine had more than 200 different antigenic proteins. In the 1980s, the seven vaccines routinely given to children contained thousands of antigens. Today, the number of antigens contained in all the vaccines given to a child by age 2 is less than 315. In contrast, it’s thought a child most likely fights off 2,000 to 6,000 antigens every day from the environment.

Yes, we’re giving more shots, but a child’s immune system has to do far less work to respond to them than in the past.

Spacing out vaccines provides no benefit, and leaves children susceptible to illnesses for a longer time. It also requires more trips to the doctor, each of which is a chance to be exposed to other sick children. In addition, studies show that spacing out vaccines reduces the likelihood that children will complete the full schedule of immunizations.

Finally, Mr. Carson intimated that some shots are lifesaving, and some might be more “optional.” All of the shots recommended by the Centers for Disease Control have been judged to be important. I know of some people who think that the varicella, or chickenpox, vaccine is one of the “less important” ones. Tell that to my father, who contracted the illness as an adult when my siblings and I did, and almost needed to be hospitalized. Or tell that to the many babies who might catch the disease before they can get the shot and become severely ill.

In one of my favorite studies on this topic, researchers looked at how many children died of varicella before and after the introduction of the vaccine in 1995. Between 1990 and 1994, more than 45 children died with varicella as the underlying cause. From 2003 to 2007, only 10 did. Even more significantly, in that latter period only one child younger than 1 died with varicella as the underlying cause, and none after 2004. Remember that not one of those infants was vaccinated. That result came about only from herd immunity: when enough people are vaccinated to protect those who can’t be.

All of the vaccines save lives.

It would be better for our vaccination policy for this not even to be a topic for debate, certainly not by those who aren’t immersed in the science of vaccines.

Debating any of these facts does no one any good.


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