Age-specific risks of varicella complications.

Previous estimates of the age-specific risks of varicella-associated encephalitis and death (the only two varicella complications for which national data are available) have been based on age data for varicella cases from only three reporting areas. In an attempt to estimate more accurately the age-specific risks, 1978, age data for varicella cases were solicited from state epidemiologists. These age-specific data were compared to those from the three original reporting areas and from the National Center for Health Statistics Health Interview Survey (HIS) for the time period 1972 to 1978. The age distribution of state and HIS cases was then compared with that of encephalitis cases and deaths reported between 1972 and 1978 to the Centers for Disease Control and the National Center for Health Statistics, respectively. Despite differences in the number and distribution of varicella cases, both sources clearly identified those greater than or equal to 20 years of age as having the greatest risk of varicella encephalitis or death. Young children also were at increased risk. A number of problems with the reliability and accuracy of the data indicate that more specific data are needed to delineate further the groups most at risk of varicella complications who might benefit most from vaccination, and to evaluate accurately the effects the vaccine might have.