Varicella (chickenpox) is a highly contagious viral disease caused by the varicella-zoster virus. It is characterized by an itchy rash made up of fluid-filled blisters that eventually scab over. Other symptoms that commonly appear 1 to 2 days before the rash include fever, headaches, and a runny nose. In severe cases, varicella can lead to blood infections, brain inflammation, pneumonia (lung infection), bacterial skin infections/scarring, hospitalization, and, in rare cases, death.

After you have recovered from varicella, your body does not rid itself of the varicella-zoster virus. Instead, the virus remains dormant in your body, specifically in your nerves. The virus can then reactivate later in life, causing shingles.

Varicella is spread through direct contact with the rash or the liquid from the blisters/rash, and through the air (i.e., when someone who has varicella coughs or sneezes in the same room as you and you inhale the infected droplets in the air). People will typically begin to experience symptoms 10 to 21 days after they have been exposed to the virus. Persons with varicella can infect others from 1 to 2 days before the rash appears up until all the blisters have scabbed over. Pregnant persons who become infected with varicella can pass the virus along to their unborn baby. This can lead to the baby being born with low birth weight, eye or limb abnormalities, skin scarring, or brain damage.