Unvaccinated students at a high school in eastern Michigan were told to stay home following an outbreak of chickenpox at the school.

In a notice this week, the St. Clair County Health Department, along with the Michigan Department of Health and Human Services, announced the outbreak at Marysville High School. The announcement detailed that health officials, along with the Marysville school district, have identified about 37 unvaccinated students who are susceptible to the highly contagious virus.

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“In accordance with the Michigan Public Health Code, exposed susceptible students who cannot provide documentation of vaccination or immunity history will be excluded from attending school, work or extracurricular activities until 21 days after the last identified case,” officials said.

The students will be readmitted to the school after they are vaccinated or after “providing the Health Department with acceptable documentation of immunity.”

Immunity, according to the news release, is defined as documentation of two valid doses of the live chickenpox vaccine at or after 12 months of age or “lab evidence of immunity or confirmation of the disease.”

Chickenpox is a highly contagious virus that spreads when an infected person coughs, sneezes or even talks. The virus can also spread to an unvaccinated person if they come into contact with an infected person’s chickenpox blisters.

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Symptoms typically include fever, headache, lethargy and an itchy rash.

“The chickenpox (varicella) vaccine is the best protection from chickenpox. It is important to make sure you and your children’s vaccines are up to date to help prevent outbreaks and protect people who can’t be vaccinated,” Dr. Annette Mercatante, the St. Clair County Health Department’s medical health officer, said in a statement.