Epidemiology Research Today is a free monthly online journal that collates and summarizes the latest research about Epidemiology, including details on twin studies, statistics, environmental and genetic factors.

The changing epidemiology of chickenpox in Alberta.

Russell ML, Svenson LW, Yiannakoulias N, Schopflocher DP, Virani SN, Grimsrud K

Department of Community Health Sciences, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1. mlrussel@ucalgary.ca

BACKGROUND: Varicella vaccine was licensed in Canada in 1998. The province of Alberta introduced a universal publicly funded varicella vaccination program in 2001. PURPOSE: To describe the epidemiology of non-fatal cases of chickenpox for which publicly funded health services were utilized for the period 1986-2002. METHODS: We 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. RESULTS: The 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. CONCLUSION: Chickenpox 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.

Published 15 November 2005 in Vaccine, 23(46): 5398-403.
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