KEENE, Texas -- About 30 children stayed home from school Thursday in the Keene Independent School District.

Seven of those children have confirmed cases of mumps. The rest, according to superintendent Ricky Stephens, were unvaccinated and in danger of contracting the uncommon illness.

"It’s one of those things like polio and small pox," he said. "It’s just out of our minds."

In total, 10 people in Johnson County have been diagnosed with mumps this week. In addition to the Keene ISD cases, one adult was also diagnosed with the illness. Two students in the Cleburne ISD were diagnosed too.

Thursday, local officials learned more about the possible source of the outbreak.

"They believe it came from Arkansas," Stephens said. "Arkansas has had a big rash of mumps and we had some families visit family in Arkansas."

The information came from Johnson County's local health authority, Dr. Elvin Adams, who participated in a conference call Thursday with officials from both the Texas and Arkansas health departments.During that call, Dr. Adams learned the Marshallese community, people from the Marshall Islands, have been hit especially hard. He said the majority of Johnson County's cases involve members of that community.

"Mumps is one of the most contagious things we see," said Dr. Justin Smith, a pediatrician at Cook Children's Hospital. He says MMR vaccinations protect against 98 percent of cases. But News 8 has learned in this particular outbreak, the three children who traveled to Arkansas did have the vaccination.

"At least a small percentage of kids won't be protected even from two vaccines," Smith said. "Because of that, when you get enough cases in the community, they’re getting enough exposures [that] the incidence in getting it even if vaccinated does go up a little bit."

Adams also mentioned there's a chance this particular strain affecting those in Johnson County might not be fully covered by the vaccine.

Thursday afternoon, Keene ISD unloaded cases of bottled water so elementary students won't have to share the water fountain during this outbreak. They also did a deep cleaning of their schools.

Students who remain unvaccinated will have to stay home from school for 26 days, as to guarantee they have not contracted mumps. Keene ISD says about 3 percent of its student body, 34 out of 1,100, are unvaccinated. However, some of the students received vaccinations this week so they could return to school.

Superintendent Ricky Stephens says the state will likely hold an immunization clinic in Cleburne in the coming days.