Twenty kids from Huntington Beach High School in California have not been allowed to attend school since early January because they have not received vaccines that protect against measles.

Earlier this month, a student from the Orange County school was diagnosed with measles, amid a growing outbreak of the illness in the region. The Associated Press reported that 70 people in six states and Mexico have contracted the disease since mid-December, in an outbreak traced to Disneyland. Most of those who became ill are in California.

Measles is a highly contagious respiratory condition that causes a rash all over the body. Measles complications can cause more serious conditions.

After the Huntington Beach public school student was diagnosed, local health officials worked with the school district to identify students who had not been vaccinated, Orange County Department of Education Health and Wellness Coordinator Pamela Kahn told The Huffington Post over the phone. California law requires that students have two measles, mumps and rubella (MMR) vaccines before entering school, although there are loopholes that allow students to evade this rule. Zahn said the school initially identified 24 students who were not given any MMR vaccines, but narrowed that number down to 20 after some parents came forward with proof of their child’s vaccinations.

“We are very lucky in Huntington beach,” Zahn told HuffPost. “The high school has around 3,000 students, and only 20 were not immunized -– that’s less than 1 percent.”