Finally, proof that anti-vaxxers are likely causing outbreaks

Vaccines save lives—this is a matter of scientific consensus. They're incredibly safe, they do not cause autism, and they prevent diseases that ravaged prior generations. But until now, we haven't seen much evidence that parents who opt out of vaccines are causing any damage. Sure it makes logical (and poetic) sense that anti-vaxxers would get the measles. But hard data on the impact of vaccine refusal will go a long way in educating the community.

Fortunately a new, enormous study review in JAMA dug up the numbers, and it ain't pretty. Out of more than 1,400 measles cases reported between January 2000—the year measles was declared eliminated in the United States—and November 2015 researchers found that nearly 60 percent had no history of measles vaccination, most of them due to non-medical exemptions for religious or philosophical reasons. In other words, they were anti-vaxxers. The whooping cough data wasn't much better. Out of more than 10,000 pertussis patients, 24 percent to 45 percent of people in the five largest epidemics since 1977 had reportedly skipped their routine vaccines.

Scientists suspect that anti-vaxxers are also to blame for the vaccinated people who caught measles and whooping cough. "It turns out that [anti-vaxxers] also put others at risk too," Dr. Matthew Davis, a pediatrics researcher at the University of Michigan in Ann Arbor who was not involved in the study, told Reuters. "Even people who have been vaccinated before, but whose protection from those vaccinations may not be as strong as it used to be."

It's tempting to blame anti-vaxxers whenever preventable diseases resurface, but they're not always at fault. In 2012, the United States experienced one of the largest whooping cough epidemics in 50 years, yet the likely culprit was probably a new strain of bacteria or weak vaccines—not people who had refused vaccines. Still, some studies have cautiously presented data that suggests forgoing vaccinations causes epidemics. At least one recent study concluded that unvaccinated children were likely to blame for fueling the 2015 Disneyland outbreak, for instance.

But this is the first study to scour outbreaks across PubMed, painting a broad picture of the link between unvaccinated populations in the United States and preventable disease outbreaks. Researchers ultimately found 1,416 measles cases and 10,609 whooping cough cases on PubMed, and the number of people in these reports who were unvaccinated was disturbingly high—between 40 percent and 60 percent, in most cases.

This broadly confirmed a link between non-vaccination and outbreaks of preventable diseases. "The phenomenon of vaccine refusal was associated with an increased risk for measles among people who refuse vaccines and among fully vaccinated individuals," the authors write.

One disturbing hiccup in the data was that several pertussis outbreaks also occurred in highly vaccinated populations, either indicating that the vaccine isn't working as expected or that people may require booster shots. But there was still a clear link between skipping vaccines and whooping cough. "Although pertussis resurgence has been attributed to waning immunity and other factors, vaccine refusal was still associated with an increased risk for pertussis in some populations," the authors write.

To be fair, no vaccine is 100 percent effective and that could also explain why at least some of the whooping cough patients had perfect vaccination records. But the imperfection of vaccines is actually one of the best reasons to get vaccinated—your immunity could protect someone else when his or her vaccine fails.

On the other hand, as Dr. Saad Omer, epidemiologist at Emory University in Georgia and coauthor on the study told Reuters, opting out of vaccines can put even vaccinated people at risk, leading to dangerous outbreaks: "If there are a high number of susceptible or unvaccinated individuals in the community the risk of getting infected—even for vaccinated children—goes up."

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