Immune responses of elderly persons 4 years after receiving a live attenuated varicella vaccine.

Annually, for 4 years after a live attenuated varicella-zoster virus (VZV) vaccine was administered to 202 elderly (55 to > 87 years old) VZV-immune persons, the immune response of vaccinees was evaluated. Anti-VZV antibody levels were enhanced by vaccination for just 1 year. However, VZV-specific proliferating T cells in peripheral blood were increased in frequency from 1 in 68,000 to 1 in 40,000 at 1 year; VZV-responding T cells were still 1 in 51,000 4 years after vaccination. The calculated half-life of this enhanced immunity was 54 months. Age had little effect on response to the vaccine, but larger doses were associated with longer duration of enhanced immunity. Immunity in approximately 10%-15% of vaccinees, independent of dose, failed to increase with the vaccine. This might complicate the use of this vaccine for prevention or attenuation of herpes zoster in the elderly.