Iowa health officials are concerned about an increase in the number of parents who are opting not to vaccinate their children.

Parents received vaccination exemptions in the 2012-13 school year for nearly 8,000 children, which is more than triple the number from 12 years ago, The Des Moines Register reported. While the figure represents less than 2 percent of all Iowa children, health leaders say they are worried about the rise in unvaccinated children.

Rick Kozin, Polk County's public-health director, said some parents might not realize that unvaccinated children could lead to a disease outbreak in schools.

Iowa laws allow two kinds of exemptions, and they are for medical or religions reasons.

Some children avoid vaccinations for medical reasons, such as allergies. Less than a third of Iowa's vaccination exemptions are for a medical reason, which must be verified by a health care professional.

The rest are classified as religious exemptions, which only requires a parent to sign a statement saying the immunizations conflict with their religion.

Spokeswoman Amanda Lewis, of Des Moines Public Schools, said district leaders are aware of such statistics.

"We certainly hope that parents in our district or anywhere in Iowa do not abuse this exemption, as it is relatively easy to obtain and impossible to confirm," she said.

"The district strongly believes that the immunization of students is an important public health issue that impacts the well-being of our students as much as any other safety measure we take in our schools."

Iowa has ranked well in national vaccination reports. A 2012 CDC report shows more than 93 percent of Iowa toddlers received shots for measles, mumps and rubella, which was about 2 percent higher than the national average.