Updated

Health officials in Spokane, Washington are warning students and teachers who aren’t vaccinated to stay home as the city battles a massive mumps outbreak that has sickened at least 80.

Fox 28 reported that the Spokane Regional Health District reported the rise, from 76 cases at last count, that affects 20 schools in four districts. The majority of the cases affect school-age children.

Mumps causes muscle pain, loss of appetite, fever, headache and swollen glands, according to the Centers for Disease Control and Prevention (CDC). The virus can lead to brain infections, including meningitis, deafness, as well as painful swelling of the ovaries or testicles, and, in rare cases, sterility.

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To prevent mumps, for most people, the CDC recommends the first dose of the MMR vaccine— which protects against measles, mumps and rubella—at 12 to 15 months of age, and the second dose at 4 to 6 years. In some cases, individuals can get the second dose earlier as long as it’s at least 28 days after the first dose.

Although all states require children to be vaccinated against certain communicable diseases to attend school— usually both private or public— states can establish their own vaccination exemption laws. In Washington, parents may opt their children out of vaccination with “a statement to be signed by a health care practitioner stating that he or she provided the signator with information about the benefits and risks of immunization to the child,” according to the CDC.