Hepatitis B virus markers among teenagers in the Araguaia region, Central Brazil: assessment of prevalence and vaccination coverage.

The Brazilian hepatitis B (HBV) vaccination program for neonates was implemented in 1998 and broadened to include young people up to 20 years of age in 2001. However, HBV coverage of teenagers has not been systematically assessed in Brazil. A cross-sectional study was performed to estimate the magnitude of HBV infection and vaccine coverage among adolescent students regularly enrolled in the public schools of Barra do Garças, a city located in the state of Mato Grosso, Brazil. A representative sample was randomly obtained and participants were interviewed and had blood samples collected to test for HBV markers. The sample was composed of 576 subjects, 51% of which were females. The average age was 15, with the group ranging from 12 to 20 years of age. There were 29 anti-HBc reactive participants (5.0%). Four out of 29 were HBsAg positive (0.7%). Anti-HBs alone (vaccinated profile) showed in 323 (56.1%) students and 224 (38.9%) were negative for all HBV markers. Increasing age was associated with HBV exposure in a χ(2) for trend analysis (p=0.004). The prevalence of anti-HBs alone decreased as the subjects' age increased. Multivariate analysis showed independent association between HBV infection and the start of sexual activity. Another associated variable was the fact that the some students were enrolled in two low-income neighborhood schools. Our findings classify this area as low endemic for HBV and suggest that there is a progressive decrease in the spread of HBV in the region due to the introduction of universal vaccination of neonates. Approximately half of the adolescents 15 years or older were not immunized, which raises a concern in terms of the need to increase the vaccination rate for this segment of the population.