Immunologic and epidemiologic aspects of varicella infection acquired during infancy and early childhood.

The development of varicella zoster infection was studied in a population of infants under one year of age during three outbreaks of varicella in a semi-closed domiciliary institution for infants in Japan. Over a period of four years, many residents ranging in age from 27 days to 32 months were tested for cutaneous reactivity to VZV antigen, and VZV-specific antibody activity before, during, and after each outbreak of varicella. Of these, 85 subjects developed clinical varicella, with an overall attack rate of 100% for all susceptible subjects. All the infants under 2 months of age were infected following such exposure, despite the presence of pre-existing maternal antibody. The degree of cutaneous involvement appeared to be milder (less than 20 vesicles) in infants less than 2 months of age, and severe cutaneous disease (with over 300 eruptions or confluent rash) occurred more frequently in subjects 2 to 11 months of age. Pre-existing antibody did not prevent development of illness, or alter the degree of antibody or cellular immune response to subsequent infection. However, the peak cutaneous reactivity to VZV antigen after infection was found to be significantly lower in infants under 2 months of age.