Pregnant celebrity tattoo artist Kat Von D is under fire after declaring she wants a “natural” and “vegan child, without vaccinations” in a recent Instagram post. She is one of many controversial celebrities who have supported the anti-vaccination movement, which has been denounced by health professionals but nevertheless adopted widely in many parts of the United States, as a new study in PLOS Medicine shows. In the paper, researchers point out the US “hot spots” where anti-vaccination ideology creates outbreak-vulnerable zones.

These zones are those where state officials permit vaccine nonmedical exemptions (NMEs), based on “philosophical belief,” as the researchers write in the paper. In these states, parents who don’t want their kid to take part in vaccinations required for school can apply for an NME.

Since 2009, the researchers note, the number of NMEs handed out has risen in 12 of the 18 states that allow such exemptions, and in those states, the rate of mumps-measles-rubella vaccination has indeed decreased. They also note that, according to the 2015 National Immunization Survey, only 72.2 percent of children between the ages of 19 and 35 months were immunized properly, according to the guidelines from the Advisory Committee on Immunization Practices.

The 18 states that currently hand out NMEs, shown in the map below, include Arkansas, Arizona, Idaho, Maine, Minnesota, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Texas, and Utah.

NME PLOS Medicine
Red zones show the rise in NMEs in the 18 states that permit it.

The anti-vaccination movement is dangerous not only because it makes individual children vulnerable to infection with disease but also because it makes the entire population vulnerable. This concept is described by the term “herd immunity,” which Inverse explained previously:

Vaccination works best when it occurs on the population level, conferring what scientists call “herd immunity”: The idea is that when the majority of the herd is vaccinated against a disease (so they can’t get infected), they act as a buffer against the minority of individuals who do get infected, thereby preventing the disease from affecting the entire herd. The infection-prone minority often consists of — surprise — young children and infants, whose immune systems aren’t as well-equipped to fight off disease.

The anti-vaccination movement is poking holes in America’s safety net, the researchers write: “The target vaccination coverage rate to achieve the ideal herd immunity is 90% to 95%, depending on the infectious agent.”

The team also pointed out that anti-vaccination is starting to take root in many major metropolitan areas. This may be especially dangerous because of the higher density of people in these areas, which could increase the likelihood that any individual will contract disease.

“The high numbers of NMEs in these densely populated urban centers suggest that outbreaks of vaccine-preventable diseases could either originate from or spread rapidly throughout these populations of unimmunized, unprotected children,” the team writes. “The fact that the largest count of vaccine-exempt pediatric populations originate in large cities with busy international airports may further contribute to this risk.”

anti-vaccination cities
Anti-vaccination has taken root in many metropolitan areas, as this tally of counties with >400 NMEs shows.

Unfortunately, the average rate at which NMEs are being handed out seems to have accelerated the most between 2009 and 2014, and in some states, those numbers are still rising, the team writes. The growing popularity of the anti-vaccination movement has been blamed in large part on celebrities, like Kat Von D and Gwyneth Paltrow, who tout it as a safer, more natural way to raise children and blame vaccines for causing diseases like autism. The research that the anti-vaccination movement was initially founded on, however, has been completely debunked; Andrew Wakefield, who published the initial fraudulent paper linking vaccination and autism in The Lancet in 1998, has been excommunicated from the medical community.

Anyone that needs further proof that anti-vaccination is not a safe way to raise a child doesn’t have to look much further than the kids who have been affected by measles and mumps — two diseases that America had long kept under control, thanks to vaccination — in recent years. In response to Kat Von D’s Instagram post, beauty blogger Caroline Hirons made headlines by posting photos of her own son after he was hospitalized with mumps. “These diseases were almost gone,” she wrote in her Instagram post, “now they are back because some people think they know better than all the scientists, physicians and specialists in modern science.”