Immune response to secondary immunization with live or inactivated VZV vaccine in elderly adults

Healthy varicella zoster virus (VZV) immune subjects > 55 years old, were immunized with 4,000 PFU of Oka strain VZV live vaccine or a similar amount of heat-inactivated vaccine. A subset of each group was also immunized with tetanus toxoid (TT) 3 months before receiving the VZV vaccine. The live and inactivated VZV vaccine groups had similar ages, sex distribution, and previous immunity to VZV. The live and inactivated VZV vaccines elicited similar increases in the frequency in blood of VZV-specific T cells, in vitro interferon-gamma production, and serum antibody levels both 3 and 12 months after immunization. Individuals with the highest responder cell frequency (RCF) at entry had the highest postimmunization RCF following either vaccine. There was no correlation at entry between the RCF to TT or RCF to VZV. There was a weak (P = 0.05) correlation in the incremental response to TT and VZV among individuals who responded to both vaccines. Entry variables that did not correlate with the response included percent of T cells or the CD45R0 (memory) T cell subset in blood, serum antibody levels, or amount of interferon-gamma production. The results indicate that the inactivated vaccine is safe for VZV-immune subjects and boosts their antibody and T-cell responses as effectively as the live vaccine for at least 1 year following immunization.