Live Varicella Virus Vaccine

Research summary

Clinical trials and large observational studies in healthy children, adolescents, and adults consistently show that live varicella virus vaccine is highly effective in preventing varicella. Randomized, placebo‑controlled trials demonstrate near‑complete protection against clinically diagnosed varicella in susceptible children, and subsequent post‑licensure studies and meta‑analyses report roughly 80–85% effectiveness for a single dose against any varicella and close to 100% protection against severe disease. Two‑dose regimens in healthy children and adults further improve protection, with effectiveness around or above 90% against any varicella and very high protection against moderate and severe forms. Safety data from pre‑licensure trials, phase 3 immunogenicity studies, and decades of post‑licensure surveillance indicate that the vaccine has a favorable safety profile in healthy individuals. Common short‑term reactions are mild and include local injection‑site complaints and transient fever; clinically significant adverse events are rare. Long‑term follow‑up of vaccinated populations confirms durable immunity and large reductions in community chickenpox incidence. The overall research consensus is that live varicella virus vaccine is a safe and effective preventive intervention for varicella in healthy human subjects when used according to recommended immunization schedules.