Serological and molecular epidemiological outcomes after two decades of universal infant hepatitis B virus (HBV) vaccination in Nunavut, Canada
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Date
2015-01-09
Authors
Huynh, Chris
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Abstract
Background: Chronic HBV within the Canadian Arctic is considered endemic (>2% prevalence). To control endemic rates in Nunavut, a vaccination program was initiated approximately 20 years ago, targeted at newborns and grade school students, as an interim catch-up program, such that all individuals born after 1980 are potentially vaccinated. This study investigates the efficacy of these programs and is the first seroepidemiological survey to determine HBV prevalence in Nunavut in the post-vaccination era. Methods: Anonymized serum specimens scheduled for destruction following routine medical testing were collected from individuals granting consent. Specimens were tested for antibodies to HBV (anti-HBs, anti-HBc) and hepatitis C virus. Anti-HBc positive samples were further tested for surface antigen (HBsAg) positivity, and HBV DNA was extracted from HBsAg positive samples in order to perform molecular characterization. Results: 4802 specimens were collected according to the age distribution of Nunavut, with vaccine age cohort specimens comprising just over half of all collected specimens. Overall anti-HCV+ was 0.55%, with all positivity observed among those aged 24 to 69 years old. Total anti-HBc+ prevalence was 9.40%; however, a 10-fold decrease in the rate of HBV exposure was noted among those born after 1980 compared to those born before (1.89% vs 20.1%, p<0.001). HBsAg positivity was primarily documented in individuals born before 1980 (2.55%), although cases still occurred among the vaccine age cohort (0.21%). HBV subgenotype B5 (HBV/B5), known to be unique among Inuit and Alaska Native people, was the most prevalent genotype observed (82%). Vaccine-based antibody as the sole serological marker was evident in the vaccine age cohort, although the rate of decay with increasing age was much greater than anticipated. Conclusion: Nearly two decades after the advent of HBV vaccination in Nunavut, HBV prevalence has decreased to 1.17%, indicating a non-endemic or low risk prevalence. However, the persistence of infection and a lower than expected prevalence of vaccine-based immunity in the vaccine age cohort will require further investigation to understand the causes and consequences.
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hepatitis B virus, HBV, epidemiology, vaccine, vaccination, Nunavut