Immunologic evidence of reinfection with varicella-zoster virus.

Resistance to reinfection with varicella-zoster virus (VZV) was evaluated in immune adults who had household exposure to varicella. Sixty-four percent of 25 adults exposed to varicella had a fourfold or greater rise in IgG antibody to VZV or had a high initial IgG antibody titer to VZV that declined by fourfold. IgM antibody was detected in only 12% of 25 VZV-immune subjects. Seventy percent of 23 subjects exposed to varicella had IgA antibody to VZV compared with 13% of 23 subjects with antibody to VZV who had no recent exposure (P less than 0.001, chi 2 test). Enhanced cellular immunity was documented by an increase in lymphocyte transformation to VZV antigen from a mean +/- SE index of 7.8 +/- 1.30 to 15.3 +/- 2.56 (P = 0.01, paired t-test). The increase in immunity to VZV in many immune subjects exposed to VZV suggests the occurrence of subclinical reinfection.