According to recently released federal health data, more parents in the United States are choosing to exempt their children from recommended vaccinations. Children in the US are routinely vaccinated against 14 potentially serious illnesses. However, a recent upswing in vaccine skepticism seems to be convincing more parents to forego these vaccinations.

The percentage of children under 2 years old who haven’t received any vaccinations has quadrupled in the last 17 years. The Centers for Disease Control and Prevention released a report that showed 1.3 percent of 19- to 35-month-old children had not received any of the recommended vaccinations. That was up from 0.9 percent in 2011 and 0.3 percent in 2001.

A second report showed the percentage of children entering kindergarten in 2017 exempted from immunization requirements reached 2.2 percent, the third consecutive school year the percentage has increased. According to the report, the majority of exemptions are nonmedical. Most states let parents to opt their children out of school immunization requirements for nonmedical reasons.

A small but increasing number of children are not getting the necessary protection against pediatric infectious diseases. The reports cited a number of reasons why the rate of unvaccinated children has been rising. The researchers determined that health insurance, child care, transportation, and a shortage of pediatricians all played a role. The number of unvaccinated children in rural areas was double the number of unvaccinated children living in urban areas.

There are now communities of undervaccinated children who are more susceptible to disease. Last year, Minnesota suffered the state’s worst measles outbreak in decades. Most of the confirmed cases were unvaccinated Somali American children.

This unvaccinated populace can pose health risks to the broader public. Vaccine-preventable diseases, such as measles, whooping cough and chicken pox, can spread quickly among an unvaccinated population. Overall, immunization rates haven’t changed much at the national level. The vast majority of parents across the country vaccinate their children.