An increase in non-medical exemptions from childhood vaccinations in the United States has led to several geographic “hotspots” where children are more susceptible to vaccine-preventable disease outbreaks, according to a new report.

While some parents do not vaccinate their children due to medical reasons, others are choosing not to vaccinate due to philosophical beliefs – some of whom believe vaccination causes autism, according to CBS News.

A recent analysis published in the journal PLOS Medicine found since 2009, there has been an increase in the number of children enrolling in kindergarten with a non-medical exemption in 12 of the 18 states that allow non-medical exemptions from childhood vaccinations.

“Our study of vaccine exemptions find that while nationally immunization rates may not have changed much, we may have unmasked a number of both rural and urban hotspots where large numbers of children are not receiving access to life-saving vaccines,” said study author Peter Hotez, a professor at Baylor College of Medicine and co-editor-in-chief of PLOS Neglected Tropical Diseases. “Much of this reflects organized and well-funded anti-vaccine activities among 18 U.S. states that allow non-medical exemptions for reasons of personal beliefs.”

The report identified 15 metropolitan areas where more than five percent of all kindergarten-age children are unvaccinated. Those areas include Seattle, Wash., Spokane, Wash., Portland, Oreg., Phoenix, Ariz., Salt Lake City, Utah, Provo, Utah, Houston, Texas, Fort Worth, Texas, Plano, Texas Austin, Texas, Troy, Mich., Warren, Mich., Detroit, Mich., Kansas City, Mo., and Pittsburgh, Penn.

Furthermore, the study identified 10 smaller counties where more than 14 percent of kindergarten-aged children are unvaccinated – eight of which are located in Idaho.

For instance, in Camas County in southern Idaho, 27 percent of the kindergarten population did not receive childhood vaccinations in the 2016-2017 school year.

While immunization rates have not changed much at national and state levels, the new county-level data shows conditions similar to those that resulted in recent measles outbreaks in California and Minnesota, according to federal health officials.

In 2014-15, a measles outbreak was linked to Disneyland in Calif., and was associated with low vaccination coverage, reports The Washington Post.

While most vaccine-preventable diseases are not currently widespread in the U.S. due to herd immunity, the more people go unvaccinated, the more likely the disease is to become widespread. The study’s authors emphasize that 90 to 95 percent vaccine coverage is needed to protect children from measles.

“Stricter legislative action to close [non-medical exemptions from vaccination] should become a higher priority,” the study concludes.

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