This vaccine is a live but weakened form of the chickenpox (varicella) virus. Children get the chickenpox vaccine as part of their routine immunizations. Adolescents and adults who are not already immune to the chickenpox virus can also get the vaccine.

When a weak form of the virus is injected, the body's immune system reacts. It destroys the virus and makes disease-fighting proteins (antibodies) to fight the virus. The antibodies to that virus stay in the body and will keep the person from getting sick or getting severe symptoms if exposed to the virus again. The person is then considered immune to chickenpox.