The changing epidemiology of chickenpox in Alberta

BackgroundVaricella vaccine was licensed in Canada in 1998. The province of Alberta introduced a universal publicly funded varicella vaccination program in 2001.PurposeTo describe the epidemiology of non-fatal cases of chickenpox for which publicly funded health services were utilized for the period 1986–2002.MethodsWe used the records of Alberta's universal, publicly funded health care insurance system to identify cases of chickenpox for the period 1986–2002. The earliest dated utilization of a health service for which there was an ICD9-CM code of 052.xx or an IC10-CA code of B01.xx was used as the date of illness onset. Denominators for rates were estimated using mid-year population estimates from the Alberta Health Care Insurance Registry. Age-specific rates were estimated for each year.ResultsThe crude incidence of chickenpox significantly declined over the period 1994–2002, most steeply after the year 2000. The incidence of chickenpox varied by age group and year and there was evidence of age-group-year interaction. Among those aged 5–19 years, chickenpox incidence began to decline prior to vaccine licensure in Canada. Among those aged less than one year and those aged 1–4 years, the incidence increased until 1999 when a decline began. Over the period 0.8% of cases were hospitalized.ConclusionChickenpox rates began to decline prior to the introduction of the publicly funded vaccination program; however the declines in rates among the youngest age-groups are consistent with a vaccination program effect.