Chickenpox is caused by the highly contagious varicella zoster virus. It is spread by coughing and sneezing, and by direct contact with skin lesions. The risk for transmission of chickenpox among school-aged children, college students, and students in other post-secondary educational institutions can be high because of the likelihood of contact between people in this setting.

Chickenpox can lead to severe complications, including bacterial infection of the skin from the lesions, swelling of the brain, and pneumonia. Once a person has had chickenpox, the virus can reactivate later in life to cause a painful condition called shingles, marked by a blistering rash. Adults are at greater risk for severe complications from chickenpox than children.

Most, but not all, infected individuals have a fever, which develops just before or when the rash (itchy blisters on the body) appears. A person with chickenpox is contagious one to two days before the rash appears and until all the blisters have formed scabs. Chickenpox typically develops 10 to 21 days after exposure. Once a person has had chickenpox, the virus can reactivate later in life to cause a painful condition called shingles, marked by a blistering rash.

The Centers for Disease Control and Prevention (CDC) recommends two doses of chickenpox vaccine for children, adolescents, and adults who have never had chickenpox and were never vaccinated. Children are routinely recommended to receive the first dose at age 12 through 15 months and the second dose at age 4 through 6 years. Two doses of the vaccine are approximately 98 percent effective at preventing chickenpox. In the small number of people who are vaccinated, but still get chickenpox, the vaccine lessens the severity of their illness.