Occurrence of chickenpox during pregnancy in women seropositive for varicella-zoster virus.

In a group of 21 women counseled after exposure to chickenpox during pregnancy, 4 developed varicella despite initial studies showing that preinfection sera were varicella-zoster virus (VZV)-seropositive by fluorescent anti-membrane antibody, latex agglutination, ELISA, and VZV glycoprotein immunoblot assay. Further investigations showed that 2 of the 4 had low-titer (1/100), low-avidity, VZV-reactive IgG3 antibodies by ELISAs of preinfection sera. After chickenpox, these women developed primary-like serologic responses to VZV. Two women with high-titer (1/1600, 1/3200), high-avidity, IgG1 antibodies showed anamnestic serologic responses after reinfection. The criteria of protective VZV immunity remain ill-defined.