For 10 years after vaccination, severe illness due to varicella is reduced by about 95%.
Vaccination is highly protective against severe illness due to chickenpox. However, antibody titers and protection from illness wane over time after vaccination. Ongoing studies may determine whether varicella vaccination decreases the incidence and severity of herpes zoster. The vaccine contains a live, attenuated strain of varicella virus. Vaccination of those who are already immune has not been shown to increase the risk of adverse events.