Stimulation of specific immune response to varicella antigens in the elderly with varicella vaccine.

Ageing is associated with several immune defects that probably lead to the increased incidence of zoster observed after the 5th decade. In a double-blind study to assess an eventual stimulation of the specific immune response against the varicella-zoster virus by vaccination, either the Oka-strain live varicella vaccine or a placebo was administered to 30 healthy volunteers over 70 years of age, after a 4-week pretreatment period with either zinc acetate as an immunostimulant or a placebo. Specific skin delayed hypersensitivity and antibody levels measured by the fluorescent antibody to membrane antigen method were recorded at the start of the pretreatment period, just before vaccination, and two weeks or one month after vaccination. Initially decreased delayed-type responses to varicella antigens were observed when compared with reported values for younger subjects despite normal levels of skin reactivity to common bacterial antigens (Multitest). The varicella-specific responses were markedly boosted in the 3 groups by repeated skin testing. As a result, the effects of zinc pretreatment and vaccination were masked. On the other hand, treatment with zinc acetate was shown to increase tuberculin delayed reactions. Preexisting specific antibody titres were elevated and no significant changes occurred in the 3 study groups. The data suggest that it is not the potential for an immune response that is decreased in the elderly but rather the speed of the response. This might be the defect responsible for the increased incidence of zoster in this age group.