How do vaccines protect against chickenpox and its complications?

Chickenpox is caused by varicella-zoster virus, which spreads easily from person to person. The vaccine, introduced in the 1990s in several countries, greatly reduced cases, hospitalizations, and deaths from chickenpox. It also helps prevent severe complications such as bacterial skin infections, pneumonia, and encephalitis. Since the same virus can later reactivate as shingles, childhood vaccination can also change the amount of virus circulating in the population. Many countries now include chickenpox vaccine in routine childhood schedules.