Drug users' adherence to a 6-month vaccination protocol: effects of motivational incentives

Vaccines represent a new and promising avenue of treatment for drug abuse but pose new medication adherence challenges due to prolonged and widely spaced administration schedules. This study examined effects of prize-based incentives on retention and medication adherence among 26 cocaine users involved in a 6-month hepatitis B vaccination series. Participants could meet with research staff weekly for 24 weeks and receive 7 injections containing either the Hepatitis B vaccine or a placebo. All participants received $10 at each weekly visit (maximum of $240). Those randomly assigned to the incentive program received additional monetary payments on an escalating schedule for attendance at weekly monitoring and vaccination visits with maximum possible earnings of $751. Group attendance diverged after study week 8 with attendance better sustained in the incentive than control group (group by time interaction, p=.035). Overall percent of weekly sessions attended was 82% for incentive versus 64% for control (p=.139). Receiving all scheduled injections were 77% of incentive versus 46% of control participants (p=.107). A significantly larger percentage (74% versus 51%; p=.016) of injections were received by incentive versus control participants on the originally scheduled day. Results suggest that monetary incentives can successfully motivate drug users to attend sessions regularly and to receive injected medications in a more reliable and timely manner than may be seen under usual care procedures. Thus, incentives may be useful for addressing adherence and allowing participants to reap the full benefits of newly developed medications.