Varivax became the first licensed vaccine against chickenpox in the United States.
The U.S. Food and Drug Administration licensed Varivax in 1995. It uses a live, attenuated form of varicella-zoster virus derived from the Oka strain. The weakened virus can stimulate protective immunity without causing typical chickenpox in healthy people.
Before routine vaccination, chickenpox was extremely common among children. Although often mild, infection could cause serious complications, including bacterial skin infections, pneumonia, encephalitis, and dangerous disease in newborns or people with weakened immune systems. The virus can also remain dormant and later reactivate as shingles.
The United States later adopted a routine two-dose childhood schedule, improving protection compared with one dose. Varivax is different from ProQuad, which combines vaccines for measles, mumps, rubella, and varicella. It is also different from shingles vaccines, which are intended primarily to prevent varicella-zoster reactivation in adults.