Prophylaxis of varicella in high-risk children: Dose-response effect of zoster immune globulin

Immunodeficient patients who were presumed to be susceptible received zoster immune globulin prophylaxis after exposure to varicella. The highest clinical attack rate (35.9%) was seen in household contacts; the lowest attack rate (0%) was observed in children exposed at school. Among household contacts, 48 of 100 patients who received high titer ZIG (reciprocal complement fixation titer ≥2,560) developed fourfold rises in serum CF antibody between pre- and 48-hour post-treatment specimens, compared to only one of 34 patients treated with lower titer ZIG lots (P<0.001). Patients who developed fourfold antibody rises were significantly less likely to contract clinical varicella (P<0.01). Patients who received high titer ZIG also had significantly lower risks of death (P=0.025) and complications (P=0.006). Among ZIG-treated patients who contracted clinical varicella, 80% developed mild disease (<100 pox), and the median incubation period was prolonged. Immunodeficient children exposed to varicella benefit from ZIG prophylaxis and higher titer ZIG is of greatest benefit.