AGE-RELATED DIFFERENCES IN CELL-MEDIATED-IMMUNITY TO VARICELLA-ZOSTERVIRUS AMONG CHILDREN AND ADULTS IMMUNIZED WITH LIVE ATTENUATED VARICELLA VACCINE

Live attenuated varicella vaccine elicits protection against varicella -zoster virus (VZV), but adults require two doses to achieve optimal s eroconversion rates. To assess the potential role of cell-mediated imm unity (CMI), T cell proliferation to VZV antigen was compared in child ren and adults. Mean stimulation indices (SI) in two cohorts of 39 chi ldren tested 6 weeks after vaccination were 28.6 +/- 6.21 and 22.1 +/- 3.84, whereas 20 adult vaccinees had a mean SI of 9.1 +/- 0.99 (P =.0 4). Vaccinees had significant increases in CMI after a second dose of vaccine. At 1 year, VZV CMI was significantly lower in adults after tw o doses (10.0 +/- 1.13 vs, 15.6 +/- 1.77; P = .02), even though 82% of children received one dose. Limitations in the adult helper T cell re sponse to VZV antigens may explain the need for booster doses to elici t effective immunity and the more frequent occurrence of varicella whe n adult vaccinees are exposed to wild type virus.