Background. British Columbia introduced a preadolescent hepatitis B (HB) immunization program in 1992. This study documents trends in the reported rate of acute HB disease since 1992 and examines factors bearing on the rate of infection throughout the period of program implementation.
Methods. All Grade 6 students were eligible for immunization. Vaccine uptake was reported annually for every school. Acute HB infections were reported by physicians and by biomedical laboratories. Year-to-year trends were analyzed overall and by age group using the electronic public health information system and S-plus. Likelihood ratio tests were used to establish whether a variable was associated with the rate of acute HB in a given cohort. Poisson regression was applied to determine which variables were independently associated with the rate of acute HB.
Results. Immunization coverage ranged between 90 and 93% for each year between 1993 and 2001. The overall rate of reported acute HB declined from 7 per 100 000 to just more than 2 per 100 000, whereas that in 12- to 21-year-olds declined from 1.7 to 0 per 100 000 over this one decade period. In the final Poisson regression model, the rate of acute HB infection was significantly associated with year, urban region and lower vaccine uptake. There was an interaction between region and vaccine uptake such that higher vaccine uptake appeared more protective in rural than in urban regions.
Conclusions. Acute HB has been eliminated in the immunized adolescent cohort. A higher carrier rate in urban regions most likely explains the apparent difference in program effectiveness between urban and rural regions.