The rising number of unvaccinated children in the United States increases the risk of vaccine-preventable infectious disease outbreaks, researchers warn.
They examined rates of nonmedical vaccine exemptions for children, which are based on parents' religious, philosophical or personal beliefs rather than a known medical condition. As of 2016, 18 states allow nonmedical exemptions for personal beliefs.
The researchers found that among children enrolling in kindergarten, the number of those with nonmedical exemptions has increased since 2009 in 12 states, resulting in lower rates of vaccination for measles, mumps and rubella.
"Hotspots" of nonmedical exemptions include: Seattle and Spokane in Washington state; Houston, Fort Worth, Plano and Austin in Texas; Salt Lake City and Provo in Utah; Phoenix, Arizona, and less populated and rural counties in Idaho.
The study was published in the journal PLoS Medicine.
The increase in nonmedical exemptions "weakens herd immunity that protects the population at large, particularly children who are unable to get vaccinated for medical reasons,"Dr. Peter Hotez, professor and dean, National School of Tropical Medicine, Baylor College of Medicine, and director of the Texas Children's Hospital Center for Vaccine Development, said in a Baylor news release.