Preparations for AIDS vaccine trials. Incident human immunodeficiency virus (HIV) infections in a cohort of injection drug users in Baltimore, Maryland

In order to prepare for a possible trial of a preventive human immunodeficiency virus (HIV) vaccine in a population of injection drug users (IDUs) we followed a cohort to determine their HIV incidence, compliance with follow-up visits at 3-month intervals (i.e., quarterly) and their attitudes toward HIV vaccine trial participation. A population of 671 HIV-seronegative subjects were recruited from a cohort of IDUs already in follow-up in Baltimore, MD (the ALIVE study). We detected 19 seroconverters in 1677.80 person-quarters of follow-up, an annual incidence of 4.52/100 person-years. Compliance with quarterly follow-up was 93% at 6 months and 89% at 9 months. Although many subjects (n = 104) are not yet due for their 12-month visit, compliance to date has been 76%. The most sensitive risk behaviors associated with HIV seroconversion have been continued injection of illicit drugs and the frequency of drug use. Other reported drug associated risk behaviors, e.g., needle sharing and shooting gallery use, have decreased despite a high HIV incidence; we believe some of the reported reductions in high-risk behavior represent socially desirable responses by the study subjects. Although the difficulties in successfully doing a trial of an HIV vaccine in the population should not be underestimated, our data suggest that such a trial would be feasible.