Persistence of immunity to live attenuated varicella vaccine in healthy adults.

The varicella vaccine was approved in 1995 for use in healthy varicella-susceptible children and adults. Long-term immunity in 461 healthy adults who were enrolled in varicella vaccine trials in 1979-1999 were studied. Forty vaccinees (9%), including 19 (21%) of 89 vaccinees with household exposure (HHE) to chickenpox, developed breakthrough chickenpox 8 weeks to 11.8 years (mean, 3.3 years) after vaccination. The median number of skin lesions among the 36 untreated vaccinees was 20 (range, 1-240 lesions), and the number of lesions was essentially the same with time since vaccination. Breakthrough chickenpox was mild, even among vaccinees who did not have seroconversion or those recipients who lost detectable antibody. Lower varicella-zoster virus (VZV) antibody titers measured within 3 months of vaccination as well as at the time of HHE were associated with an increased risk of breakthrough disease. This study demonstrated that the varicella vaccine was effective in providing adults with long-term protection from serious VZV disease.