Drug users' participation in a free hepatitis B vaccination program: demographic, behavioral, and social-cognitive determinants.

The present study was conducted as an evaluation of a two-year pilot program started in 1998 in the Netherlands to provide free hepatitis B vaccination targeted at drug users (DUs). In order to identify which demographic and social-cognitive factors predict vaccination uptake, written questionnaires were distributed in three pilot regions (Amsterdam, Tiel, and Maastricht) amongst all DUs that were invited to participate in the program during a 2-month period. Vaccination behavior 2 years later was anonymously and prospectively linked to the questionnaire data, which allowed us to investigate which factors predict vaccination behavior. Of the 207 DUs eligible for vaccination (i.e., who were not immune and/or had no current infection with the virus), 93 DUs had obtained vaccination in the 2 years following the questionnaire. More than half of them (N = 50) had completed the full program (3 injections). As possible predictors of vaccination uptake, the questionnaire included constructs of the Theory of Planned Behavior as well as of the Health Belief Model. Our results show that attitude toward obtaining hepatitis B vaccination was positively associated with intention toward obtaining hepatitis B vaccination. However, perceived behavioral control was found to be the only construct related to actual vaccination uptake. None of the demographic variables were related to vaccination uptake. Our findings suggest that future interventions aimed at increasing uptake of vaccination against hepatitis B in DUs should address DUs (perceived) control concerning this behavior. The study's limitations are noted.