ALLENDALE TOWNSHIP, Mich. (WOOD) — A spokesperson for Grand Valley State University has confirmed that a “small cluster” of chickenpox infections have been reported at the school’s main campus in Allendale Township and the Pew campus in downtown Grand Rapids.

Students were notified Monday night about the rise in cases. They were urged to visit the campus health centers if they experienced any symptoms and to ensure they were vaccinated against the virus.

“Many people are immune to chickenpox because they have either had the disease or have had two doses of the chickenpox (varicella) vaccine,” the university email read. “Students who are unsure if they have had the vaccine are urged to contact their families or their health care provider to find out. People who have not been vaccinated should contact their health care provider, the Campus Health Center or the GVSU Family Health Center to schedule a vaccine.”

Chickenpox is a highly contagious disease caused by the varicella-zoster virus that typically causes a full-body rash of itchy blisters.

The virus was once quite common in the United States. According to the Centers for Disease Control and Prevention, an average of 4 million Americans were infected each year before a vaccine was developed and approved by the Food and Drug Administration in 1995. Now, an average of only 500,000 cases are reported annually across the country.

The varicella vaccine is considered safe and effective for children at least 1 year old. Prior to the vaccine, many parents would intentionally help their children get infected because cases were much less dangerous in children than in infants, adults and people with weakened immune systems.

Before the vaccine, anywhere from 10,500 to 13,000 people were hospitalized annually and 100 to 150 people died each year from chickenpox. With the vaccine, those numbers are down to 1,500 to 4,000 hospitalizations and 50 deaths per year.