A randomized controlled trial of monetary incentives vs. outreach to enhance adherence to the hepatitis B vaccine series among injection drug users.

BACKGROUND Injection drug users (IDUs) are at high-risk for hepatitis B virus (HBV) and HIV. Due to concerns about non-adherence to multi-dose vaccine regimens however, IDUs are severely under-immunized against HBV and have been excluded from phase III trials of multi-dose candidate HIV vaccines in the United States. METHODS Through a randomized controlled trial, we compared the effectiveness of monetary incentives versus outreach to improve IDUs' adherence to the 3-dose hepatitis B vaccine. In 1998-1999, HBV-susceptible IDUs were recruited from San Francisco streets. Eligible participants received their first dose of vaccine and were randomized to either receive monthly monetary incentives (n=48) or maintain weekly contact with an outreach worker (n=48) during the 6-month vaccine series. RESULTS All 3 doses of vaccine were received by 33 (69%) of IDUs in the monetary incentive arm and 11 (23%) in the outreach arm (odds ratio=13.8; 95% confidence interval, 2.9, 128; P<0.0001). In a multivariate model, receiving monetary incentives was independently associated with vaccine completion (AOR=10.3; 95% CI=3.7, 29.0). CONCLUSIONS Among IDUs, monetary incentives are superior to outreach in achieving adherence to the multi-dose hepatitis B vaccine series. Monetary incentives may be adapted to future multi-dose candidate HIV vaccine trials in IDUs.