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Why Expanding Vaccine Exemptions Hurts Herd Immunity, According To Science

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Since Nov. 9, much of the world has pondered all the ways that President-elect Donald Trump could make life harder for people (or like, bring upon the end of the world?). Nuclear war brought on by a late-night Twitter rant? Tens of thousands of Americans losing access to health care? Straight-up selling America to Russia? Or perhaps a whole generation of children dying from preventable disease? That last scenario is becoming ever more likely, now that Trump has invited a once-disbarred lawyer and conspiracy theorist with no scientific education to chair his vaccine safety commission. Expanding vaccine exemptions hurts herd immunity, which means that even those who do get vaccinated may soon be in grave danger.

Trump has long subscribed to the completely false notion that childhood vaccinations cause autism – he's tweeted about it more than 30 times – despite the fact that study after study has shown that it's simply not true. Autism was originally blamed on the preservative thimerosal. Despite the FDA finding "no evidence of harm from the use of thimerosal as a vaccine preservative," it was removed from all childhood vaccines (except some flu vaccines) between 1999 and 2001 in response to rising concerns about mercury exposure. Incredibly, many people still insist that vaccines are dangerous.

While some parents claim that it's their right to leave their own children unprotected from easily preventable diseases such as chicken pox, measles, and whooping cough, the bigger problem is that they're not just endangering their own children. When the vast majority of the population is immunized to a particular disease, the likelihood of any individual coming into contact with said disease is nearly eradicated, so even those who aren't immune are protected. For people who can't be vaccinated due to age, pregnancy, allergies or illness, this is the difference between life and death.

This is not hyperbole. Chicken pox, measles, whooping cough, influenza, polio, pneumococcal disease, tetanus, meningococcal disease, and hepatitis B can all lead to death. Autism cannot. That means that even if vaccines did increase the risk of autism, they would still be worth it. When parents choose to put their children at risk for a host of deadly diseases rather than the imagined risk of autism, it's not only ignorant, it's deeply ableist. It's implicitly telling the world, "I'd rather have a dead child than an autistic one."

Figuring out what percentage of the community needs to be vaccinated depends on a disease's reproduction rate, or how contagious it is. In the above example, a contagious person goes on to infect, on average, four more people. If nobody is immune, those four people will each go on to infect four more, meaning all 21 patients become infected. But if 75 percent of the population is immune, Patient Zero can only infect one person, who in turn goes on to infect one more, resulting in three sick people, rather than 21. It's important to note that some diseases are more contagious than others. For example, measles has a reproduction rate of 12 to 18, requiring a herd immunity of 83 to 94 percent.

However, those models are based on a completely randomized community, whereas in the real world, birds of a feather flock together. While 91.5 percent of U.S. children are vaccinated against the measles overall, that number plummets in certain sub-communities, such as California private schools, which is why we're still seeing outbreaks. Therefore, nobody who is medically able to be vaccinated should attempt to rely on herd immunity alone; doing so effectively weakens the entire herd.

And one more time for those in the back: vaccines absolutely do not cause autism, and they never did. The idea that they ever did was based on a fraudulent "study" of 12 children by Andrew Wakefield, a British doctor who has since lost his medical license. The study was not erroneous; it was fraudulent. Wakefield (who was a gastroenterologist, not a neurologist or immunologist) falsified data in order to appease his funders, a group of lawyers looking to build a case against vaccine manufacturers.

On Tuesday, Trump held a meeting with self-styled vaccine "expert" Robert F. Kennedy Jr., a man who once wrote an article on vaccines for Salon and Rolling Stone that was so littered with inaccuracies, it was continually corrected until finally being pulled completely. A man who, at a 2015 screening of the anti-vaccine propaganda film Trace Amounts, compared vaccines to the holocaust. A man who claims that those who advocate for vaccines are in the pocket of Big Pharma, while in the same breath urging those who wish to learn "the truth about vaccine science" to buy his book. Trump and Kennedy are not scientists, they're not doctors, and their promotion of vaccine exemptions could put 74 million children in danger.