Anti-Vaxxers Are Destroying the Herd Immunity They Rely On

8.7 million kids the U.S. aren’t fully immunized, and if that number grows, endemic diseases like measles could make a big comeback.

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What if enough vaccine-refusing parents failed to immunize their kids that the herd immunity they rely upon finally broke down? What if not enough people made the right decision, not just for their own families, but for the community as a whole to keep everyone protected? We may be on the cusp of finding out.

According to a new study presented last week in San Diego at the annual IDWeek conference of infectious disease specialists, about 12.5 percent of American children and adolescent have not been adequately vaccinated against measles. Nearly 5 percent of 17-year-olds have received no doses of the vaccine at all.

Using data gathered over several years from the Centers for Disease Control’s National Immunization Survey-Teen, which collects information about vaccines for 18,000—20,000 teenagers annually, researchers from Emory University reported that 8.7 million children in this country are not fully immunized. What makes the new study striking is that the findings indicate we may be on the brink of losing herd immunity.

Because no vaccine is perfect, not everyone who receives it develops an adequate response. This objection is commonly cited by those who oppose immunizations as a reason not to get them, though presumably those same people still use computers and drive automobiles despite their lack of perfect functioning at all times. Furthermore, there are people who have legitimate medical reasons for being unable to receive immunizations, such as having a condition or taking medication that weakens the immune system. Still others are simply too young to receive them.

For this reason, a certain number of people in the population as a whole need to be vaccinated in order to protect everyone. In the case of a highly contagious, airborne disease like measles, that number has been estimated at about 95 percent. Parents who refuse to vaccinate their kids are piggy-backing on the responsible choices of that same 95 percent in order to keep their own children protected, a situation those who cater to such freeloaders are all too happy to exploit.

The free ride may not last for much longer. The authors of the study estimate that if current vaccination rates were to dip to just 98 percent of where they are now, one child in seven would be vulnerable to measles. Were that pattern to be sustained, no population of children would be vaccinated to a sufficient degree to reach the threshold for reliable herd immunity.

“We know some parents have concerns about vaccines and may want to avoid or delay vaccination, or follow an alternative schedule than the one recommended because they’re concerned about the safety of the vaccine,” said Dr. Robert Bednarczyk, lead author of the study and assistant professor at Emory’s Rollins School of Public Health, in a statement. “In fact, the vaccine is very safe, while not vaccinating is highly risky, leaving their children—and others—vulnerable to a serious illness that can cause a large number of complications. Currently, these children are protected because of the high vaccine coverage of the population, but that will change if we begin having more outbreaks and the percentage of children vaccinated declines.”

It’s important to note that this new study was presented at a conference, but has not yet been published in a peer-reviewed journal. When evaluating any new source of medical information, particular scrutiny should be paid to those that haven’t yet reached that step of scientific vetting.

However, these new findings comport with what has already been observed, and with the warnings that public health officials have been making for some time. Despite measles having been declared eliminated as an endemic disease in the United States in 2000—meaning there was no longer continuous infections within this country and new cases would need to be imported rather than home-grown—the last few years have seen an alarming number of new outbreaks thanks to pockets of under-vaccination. One such outbreak that started in Disneyland earlier this year sickened 117 people.

Tragically, sooner or later enough people will fall ill that this thoroughly preventable illness will start causing fatalities. Earlier this year it was reported that a woman taking immune-suppressing medication became the first American person in a dozen years to die of measles. In Germany, an unvaccinated toddler died of the disease in February. His case was similar to that of a 6-year-old boy in Spain who died of diphtheria this summer, that country’s first case in nearly three decades, due to his parents’ decision to believe the wholly false rhetoric questioning the safety of the vaccine against it.

When parents stop vaccinating their kids against preventable illnesses, they come back. Using other people’s responsible decisions as a means of obviating your own is not only flagrantly self-serving, but destined to fail as a reliable strategy.

This new study warns that we are far too close to let trends in vaccine-refusal continue. With a dip of 2 percent from current levels, the threshold for protection could be lost, and diseases once declared eliminated could come back.