Epidemiology of varicella zoster virus infection in Canada and the United Kingdom

Many countries are currently studying the possibility of mass vaccination a gainst varicella. The objective of this study was to provide a comprehensiv e picture of the pre-vaccine epidemiology of the varicella zoster virus (VZ V) to aid in the design of immunization programs and to adequately measure the impact of vaccination. Population-based data including physician visit claims, sentinel surveillance and hospitalization data from Canada and the United Kingdom were analysed. The key epidemiological characteristics of va ricella and zoster (age specific consultation rates, seasonality, force of infection, hospitalization rates and inpatient days) were compared. Results show that the overall epidemiology of varicella and zoster is remarkably s imilar between the two countries. The major difference being that, contrary to Canada, the epidemiology of varicella seems to be changing in the Unite d Kingdom with an important decrease in the average age at infection that c oincides with a significant increase in children attending preschool. Furth ermore, differences exist in the seasonality between the United Kingdom and Canada, which seem to be primarily due to the school calendar. These resul ts illustrate that school and preschool contact patterns play an important role in the dynamics of varicella. Finally, our results provide baseline es timates of varicella and zoster incidence and morbidity for VZV vaccine eff ectiveness and cost-effectiveness studies.