On the whole, fewer US families have opted out of school-required immunizations in recent years, thanks in part to stricter state laws.

But data from the Centers for Disease Control and Prevention indicate that, while nonmedical exemptions (which includes religious and philosophical opposition) are on the decline nationally, they’re rising in certain states, including states that haven’t previously been considered hotbeds of anti-vaccination sentiment — which may put those areas at risk of a disease outbreak.

CDC data going back to 2009 indicate a sharp spike in nonmedical exemptions in the 2013-2014 school year, when nearly 80,000 US kindergarteners were exempted from receiving at least one vaccine.

Exemptions since then have fallen to around 72,000 last school year. California alone saw a drop of more than 3,000 exemptions after it eliminated personal belief exemptions in 2015. Vermont also removed philosophical exemptions in 2015.

But in a number of other states, nonmedical exemptions have continued to rise. In 11 states — Connecticut, Florida, Iowa, Kentucky, Maryland, New York, North Carolina, North Dakota, Ohio, Oklahoma, and Virginia — the number of kids not being vaccinated for nonmedical reasons is higher than at any point in the past five years. (With the caveat, however, that CDC data for the 2010-2011 school year is unavailable.)

Medical exemptions have long been in place for those with compromised immune systems or other conditions that make vaccines more dangerous than beneficial. But in the last decade, many states have expanded vaccination exemption laws, allowing families to forgo inoculation with MMR, Tdap, and other vaccines. (States have different vaccine requirements, but as a baseline all 50 states and the District of Columbia require diphtheria, tetanus, pertussis, polio, measles, and rubella vaccinations.)

The American Academy of Pediatrics last year issued a position statement urging all states to eliminate nonmedical vaccine exemptions, writing that such exemptions are “inappropriate for individual, public health, and ethical reasons.” As it stands, all but three states — Mississippi, California, and West Virginia — still allow philosophical and/or religious exemptions.

“North Dakota is one of the easiest states to claim a nonmedical exemption,” said Molly Howell, North Dakota’s immunization program manager. Her state’s nonmedical vaccinations went from 0.8 percent in 2010 to 3 percent last year. “At some schools, they just hand out the exemption forms.”

And parents take advantage of the option, even as some states have tried to temper their exemptions with rules excluding unvaccinated children from school during an outbreak or requiring physician signatures.

“Some people with an MD are perfectly willing to write or sign a note, for a price,” said Dr. Jesse Hackell, a pediatrician and researcher who co-authored a 2016 report on vaccine hesitancy.

Hackell suggested that anti-vaccine advocacy groups are driving the growth in exemptions by rallying parents around fears of vaccines causing autism or other conditions. Scientists have thoroughly debunked such claims.

Although they are watching the numbers carefully, state immunization managers say that they’re not yet worried.

Connecticut, for instance, saw nonmedical exemptions rise from 0.8 to 1.7 percent in the six-year period. Mick Bolduc, epidemiologist for Connecticut’s immunization program, said simply, “It’s something we’re gonna keep an eye on.”