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21 High Adherence by Drug Users to Vaccine Research: A Randomized Trial of Cash Incentives vs. Outreach among Street-Recruited Injection Drug Users
K. H. Seal, A. H. Kral, A. McNess*, L. Gee, J. Lorvick, and B. R. Edlin
Univ. of California, San Francisco, USA
Background: A substantial portion of the HIV epidemic worldwide is attributable to injection drug use, and therefore the efficacy of candidate multi-dose HIV vaccines in injection drug users (IDUs) is of critical scientific importance. HIV vaccine trials have included few active IDUs however, largely due to concerns about adherence. Nevertheless, if an efficacious vaccine is found, the ability to administer the vaccine to IDUs will become a paramount logistical consideration. We compare the effectiveness of 2 strategies, cash incentives vs. community-based outreach, to improve IDUs’ completion of the 6-month hepatitis B vaccine series.
Methods: From October 1998 through December 1999, 366 IDUs recruited from street settings in 2 inner-city neighborhoods in San Francisco were tested for sero-markers for hepatitis B virus (HBV). Participants negative for HBsAg and anti-HBs were offered vaccination. Participants received their first vaccine dose at enrollment and were randomized into 2 follow-up arms to receive the remaining doses. In the cash incentive arm, participants received $20 each month for 6 months at a community field site. In the outreach arm, an outreach worker maintained weekly contact with participants. All participants were treated nonjudgmentally and respectfully and received information about safer sex and injecting practices.
Results: Of 366 IDUs, 74 (20%) were negative for all 3 HBV markers and 75 (21%) had anti-HBc only. Of the 149 eligible for vaccine, 96 (64%) accepted their first dose and were randomized into the cash incentive (n = 48) or outreach (n = 48) arm. The median age was 44 years; 56% were male; 46% were African American, 32% white, and 15% Latino; 47% were homeless. Adherence to the second vaccine dose at 1 month was 96 and 63% in the cash incentive and outreach arms, respectively (p < 0.0001). Adherence to the third vaccine dose at 6 months was 69and 23% in the cash incentive and outreach arms, respectively (p < 0.0001).
Conclusions: IDUs will enroll in vaccine research and most can be retained with modest cash incentives. Incentives are superior to community outreach in achieving adherence to the 3-part hepatitis B vaccine series. IDUs can adhere to multi-visit vaccine dosing schedules when conditions are optimized.
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