Hepatitis B vaccination in the Columbian Amazon : effectiveness and factors influencing vaccine coverage
A vaccination coverage survey was carried out in the Colombian Amazon, a former high endemic area for hepatitis B, involving 3573 children less than II years old. It was carried out in Leticia, Puerto Narifio, and Araracuara, both urban and rural areas. Children were selected using a one stage cluster sampling, randomly selecting clusters in urban and rural areas where all children under 11 were surveyed. At the same time blood samples were taken from all children with known vaccination status (n=1603), and from their mother, when she was available (n=8l2). These samples were processed for hepatitis B surface antigen (HBsAg), antibodies to hepatitis B core antigen (Anti-HBc) and antibodies to HBsAg (Anti- HBs). A sample of children without vaccination data available was also bled to compare their results with those of children with vaccination data. Full vaccination coverage was found to range between 39% and 69% among different areas while hepatitis B vaccination ranged between 73% and 95%. Factors which improve the likelihood of being fully vaccinated in this study were: Age above one year, living in Leticia, being. affiliated to the social security, mother's years of schooling. Health worker's knowledge on vaccine contraindications and perceptions of logistical barriers against vaccination or importance of hepatitis B as a public health problem were also related to full vaccine coverage. Prevalence of hepatitis B infection reached 5% among those who were bled (8211603) while HBsAg positive status was 1.6% (26/1603). Since the introduction of the vaccine prevalence of hepatitis B infection has fallen from 40%, an 85% reduction, while carrier prevalence has fallen from 5%, a 68% reduction. Age above 7 years, living in a rural area, birth delivery supervised by other than a MD or nurse, and being born from an Anti-HBc+ mother were the most important general factors related to being infected with HBV. Having an incomplete schedule for hepatitis B vaccine was associated with an increase in the risk of being Anti- HBc or HBsAg+. However, some characteristics of the vaccination process were related to being HBsAg+/Anti-HBc+. Delays in receiving the first dose of hepatitis B after birth and delays to receiving the second dose after the first dose were associated with an increased risk of being HBsAg+/Anti-HBc+. None of these characteristics were related to being Anti-Hlic+ alone. In conclusion, the introduction of a recombinant Cuban manufactured hepatitis B vaccine has produced a marked decline in the high infection prevalence of children in the Colombian Amazon area. A higher coverage has been achieved from the beginning of the program though intervals from birth to first dose and between doses are too long leading to new infections that could have been avoided. There is still room to make improvements in the control program, including the implementation of a surveillance system of the HBV serological status for pregnant women, in order to ensure better vaccination schemes for those born to infected or HBsAg+ mothers.