Unvaccinated kids could spend 25 days at home if someone at their school develops mumps - a contagious disease making the rounds in Columbus, Ohio.
At least 224 people in Franklin and Delaware counties have contracted the virus, which causes fever, aches and swollen glands.
The outbreak emerged at Ohio State University in January, but has since spread off-campus.
"Clearly we're seeing a very large number of cases of mumps associated with what was first an outbreak at Ohio State and now is now a community outbreak," said Jose Rodriguez, a spokesman for Columbus Public Health. "We continue to be concerned about those who are unprotected; those who do not have their two doses of MMR."
The MMR vaccine guards against measles, mumps and rubella. A single dose, administered around a child's first birthday, immunizes 95 percent of kids who get it, according to the U.S. Centers for Disease Control and Prevention. And a second dose, given before the child starts school, covers virtually all of the remaining 5 percent.
But not all kids are vaccinated, allowing the disease to spread through schools.
"In Columbus and Franklin County, we have at least 17 cases and growing in schools," Rodriguez said, adding that no one school has seen more than two cases yet. "That's when we are get really concerned, because then it becomes a cluster."
To quash mumps clusters in public schools, any child who has not received two doses of the MMR vaccine will have to stay home for up to 25 days if someone at their school contracts the virus.
"The incubation period of the disease can be as long as 25 days," said Rodriguez, explaining that schools were notified Tuesday of the 25-day rule. "We hope that parents will give it some consideration, and if their children aren't vaccinated, they're able to protect them before we have an outbreak."
Ohio requires public school children to be vaccinated, but allows medical and philosophical exemptions.
"Some children have medical conditions that don't allow them to get vaccines," Rodriguez said. "In the event of outbreak in a school, we want to make sure we have as many kids protected as we can."
An estimated 1.3 percent of Ohio kindergartners have non-medical exemptions, according to CDC data.
While most mumps sufferers recover after a week or two, the disease can cause serious complications like inflammation of the testicles, ovaries and brain as well as deafness, according to the CDC.
Rodriguez said he hopes the new 25-day rule will serve as a stark warning to parents about the importance of vaccines.
"We want them to know they can go ahead and get their children vaccinated now if they haven't," he said. "That way kids can stay in school and learn."