The 5-item mental health index, which has well-established reliability and validity, was used to measure emotional well-being (Stewart et al., 1988) on a scale of 0–100. An established cut point of 66 (Rubenstein et al., 1989) was used to identify participants’ emotional well-being. Social support was assessed by an 18-item scale used in the RAND Medical Outcomes Study (Sherbourne & Stewart, 1991). Individuals who reported any social support were asked whether their support came primarily from drug users, nonusers of drugs, or both. Results for the latter variable are reported because it has been more important in previous studies and had a greater association with vaccine completion than any social support. Perceived health status was measured on a 5-point scale from excellent to poor, and a dichotomous item inquired about the past 6-month hospitalization. Health status was dichotomized at fair or poor versus better health.