Chickenpox in Canada, 1924-87.

Because of the lack of an effective vaccine and the difficulty in implementing any effective control measures, physicians and public health practitioners have paid little attention to understanding the epidemiologic features of chickenpox. No data on the incidence rate in Canada are available for 1959-85. However, Ontario data suggest an overall decrease in the annual rate during the 1960s and a stable rate since the mid-1970s. High incidence rates are expected among children 5 to 9 years of age because of their susceptibility and their greater exposure in school. Low incidence rates among older age groups are expected, because most of these people have already been exposed to the virus. The disease is more serious among infants than among other children. The risk of death from chickenpox is also highest among infants. More patient-specific information and improved collection of incidence data are required to measure any impact from future control procedures, including the use of vaccines currently being developed.