Immunization of the elderly to boost immunity against varicella-zoster virus (VZV) as assessed by VZV skin test reaction.

The utility of the VZV skin test in detecting individual susceptibility to varicella and zoster was determined. Its specificity particularly with regard to herpes simplex was also established. The VZV skin test was negative or weakly positive during the early stage of herpes zoster, and strongly positive during recovery from that disease. A small-scale clinical trial to immunize elderly individuals has been performed for the purpose of preventing herpes zoster, and, perhaps, severe post-herpetic neuralgia as well. Sixty individuals > or = 50 years old were screened for VZV antibodies by IAHA test and were given a VZV skin test for cell-mediated immunity. All were seropositive, but eight were skin-test negative. Thirty-seven individuals including the eight with negative skin tests were immunized with one dose of varicella vaccine (3.0 x 10(4) PFU/dose). After 5-7 weeks, the skin test reaction showed increased positivity, with a change in score from (-) to (+, ++) in 7/8 subjects, from (+) to (++, +++) in 3/5 subjects, and from (++) to (+++) in 6/10 subjects. Enhancement of the VZV antibody titer (defined as twofold or greater) was observed in all 15 vaccine recipients with a prevaccination titer of < or = 1:16, and in 19 of 24 subjects with a prevaccination titer of > or = 1:32. These results indicate that giving live varicella vaccine with a high viral titer can induce a good boost immunity particularly cell-mediated immunity to VZV in the elderly.