As a measles outbreak that originated in Disneyland draws greater attention to state laws that allow exemptions from vaccinations, some school districts are taking steps to keep unvaccinated students out of classrooms temporarily. But public school districts that want to tighten vaccination rules to bolster prevention are out of luck, experts say.

Every state requires inoculations from diseases such as measles and whooping cough before students enter school, but all of them allow medical exemptions for cases such as weak immune systems, according to the National Conference of State Legislatures. Additionally, 48 states allow for exemptions on religious grounds and 20 allow exemptions for personal reasons, a far broader category.

Exemptions from vaccines are linked to lower rates of immunity and a higher incidence of disease. With the number of measles cases on track to top last year’s record since the disease was declared eliminated in the U.S., the reaction from states has been mixed.

There are efforts in Colorado and Mississippi to strengthen the rights of parents to choose whether or not their children are vaccinated. Mississippi is one of only two (the other is West Virginia) that only allows medical exemptions, which has resulted in virtually all young school-aged children receiving vaccinations in the state. Legislators in California, Oregon and Washington have called for weakening exemptions from vaccinations.

Unfortunately for individual public school districts that would like to take similar steps, their options are limited. That’s because state laws or regulations typically require uniform enforcement when it comes to accepting exemptions. “Districts don’t have a lot of leeway on this,” said Tammy Carter, a senior staff attorney at the National School Boards Association. “It’s a health and safety issue, and those rules are determined by the state in conjunction with departments of health.”

Analysts from NCSL and others who follow state immunization laws agree there’s likely little individual districts can do differently. “I’ve reviewed all the laws pretty thoroughly but I don’t recall [anything like that],” said Diane Peterson, the associate director for immunization projects at the Immunization Action Coalition. “I just don’t remember coming across anything like that.”

There could be greater leeway for private schools, depending on state law. A Montessori school in Michigan has drawn attention for revising its admissions policy to keep out students of parents who refuse vaccinations on personal grounds, for example.

Public schools do commonly have authority once there’s already an outbreak, though. In California, for instance, at least two districts have recently temporarily suspended unvaccinated students. California law allows for that “when there is good cause to believe that the person has been exposed” to one of the diseases requiring immunizations.

Some states go further. In Arizona, where students have also been temporarily refused, state law requires health authorities and schools to keep unvaccinated students out during outbreaks.

What these states do isn’t uncommon, Peterson said, though the authority may be limited to times of “imminent threat.” “You absolutely do see that,” she said. “The other thing that sometimes happens is a state epidemiologist has some kind of authority in statute or the commissioner of health does to implement certain procedures. They’ll use that authority to remove those children from school.”