ABSTRACT
Chiang Mai is a province in northern Thailand that started a vaccination program for hepatitis B virus (HBV) infection in 1989. In this paper, we report the long-term efficacy of this program. Of children aged 4-9 years, 65.7% had a complete course and 3.8% had an incomplete vaccination course. Urban schoolchildren had higher percentage of HB vaccination than rural schoolchildren (89.1% vs 46.9% for the complete course, p < 0.001). The overall prevalence rate of HBsAg in Chiang Mai schoolchildren was 1.2%, with no significant differences between gender (p = 0.496) and school areas (p = 0.477). Anti-HBc antibodies were detected in 6.9% of children. Overall, 26.2% of children had protective levels of anti-HBs antibodies (> 10.0 mlU/ml), and 11.2% had low levels of these antibodies (1.0-9.9 mlU/ml). Compared to previous reports, our results show a lower percentage of anti-HBs antibodies, 33.8% of children age 4 years had protective anti-HBs antibodies, dropping to 18.4% by age 9 years. Among those anti-HBs seropositive, 9.1% were anti-HBc positive, indicating a natural infection with HBV. We found a small number of children, despite adequate immunization, developed HBV infection.
Subject(s)
Antibodies, Viral/blood , Child , Child, Preschool , Endemic Diseases/prevention & control , Female , Hepatitis B/epidemiology , Hepatitis B Vaccines/supply & distribution , Hepatitis B virus/immunology , Humans , Immunization Programs/standards , Male , Prevalence , Program Evaluation , Rural Health , Thailand/epidemiology , Treatment Outcome , Urban HealthABSTRACT
Hepatitis A virus (HAV) infection is common in Southeast Asia, and most of the inhabitants acquire a lifelong immunity as a result of natural infection during childhood. However, the age-specific seroprevalence is changing with development of socioeconomic and hygiene status in this area and the infection is predicted to shift to adulthood with more severe clinical manifestations in the future. In this study, we report the present epidemiological pattern of antibody to HAV (anti-HAV) among schoolchildren in Chiang Mai, Northern Thailand. The overall prevalence rate of anti-HAV was 9.6% (11.4% in female and 7.5% in male children, and 10.8% in urban and 8.9% in rural schoolchildren, respectively). Our study, comparing with previous reports from other parts in Thailand, indicates a steady decline of anti-HAV prevalence among schoolchildren in Chiang Mai area, and discussed a possibility of an outbreak of HAV infection among urban schoolchildren.