Transplacental immunity to varicella-zoster virus in extremely low birthweight infants.

Sixteen infants in our intensive care nursery (ICN) were inadvertently exposed to an adult who presented the next day with chickenpox. Since a majority of the patients were extremely premature, we were concerned that they might not have received transplacental varicella-zoster virus (VZV) antibody, and consequently would be at risk for contracting chickenpox. Serum samples were obtained from each infant and examined for the presence or absence of VZV antibody. Fourteen of the 16 infants had antibody levels equal to or in excess of 1:16 by indirect fluorescent antibody, including six of eight infants with birthweights equal to or less than 1000 gm, and eight of ten infants with gestational ages equal to or less than 28 weeks. Passive transfer of immunity to VZV appears to be common in infants as young as 24 to 28 weeks' gestation.