Feasibility of Conducting HIV-1 Vaccine Trials in the United States: Recruitment, Retention and HIV-1 Seroincidence from the HIV Network for Prevention Trials (HIVNET) Vaccine Preparedness Study (VPS)

Background: The VPS was a prospective cohort study designed to recruit, retain and estimate HIV-1 incidence over time under, with responsible and achievable risk reduction counseling.

Methods: Crude HIV-1 incidence rates and 95% CI were calculated for socio-demographic, site, and eligibility criteria (any anal intercourse in the past year for MSM, any injection in the past 6 months for IDU or any of 6 behavioral eligibility criteria among women (WSM)). Adjusted RR were estimated using a Poisson regression.

Results: 4892 (3257 MSM, 770 male IDU, 354 female IDU, 511 WSM) participants were recruited in 8 US cities from 4/94-11/94 using the following approaches: 40% rollover from existing cohorts, 21% "snowball" techniques, 20% staff outreach, 14% media, and 4% other. At 18 months, 88% follow-up was achieved and 89 incident HIV-1 infections (1.36/100 PY, 95% CI=1.07-1.61) were observed. HIV-1 seroincidence rates varied by baseline eligibility criteria with rates of 1.54/100 PY (95% CI=1.22-1.94) among MSM, 0.38/100 PY (95% CI=0.15-1.01) among Male IDU’s, 1.15/100 PY (95% CI=0.57-2.29) among WSM and 1.26/100 PY (95% CI=0.57-2.80) among female IDU’s; and enrollment site, from 0.49/100 PY (95% CI=0.19-1.30 to 2.18/100 PY, 95% CI=1.46-3.25). Participants who were definitely willing to enroll in an HIV vaccine trial had the highest seroincidence (1.97/100 PY, 95% CI= 1.41-2.74). Varying baseline eligibility among women to include 3 or more high risk sexual behaviors (2.00/100 PY, 95% CI= 0.91-3.71) or crack use (1.70/100 PY, 95% CI=0.93-2.80) and MSM to include only unprotected anal intercourse (1.98/100 PY, 95% CI=1.51-2.60) resulted in higher HIV-1 incidence. After adjusting for eligibility, no non-site significant differences in HIV-1 seroincidence were observed.

Conclusions: MSM and women at heterosexual/injection risk, with some eligibility modifications, can be rapidly recruited, enrolled and followed under conditions comparable to a preventive HIV vaccine trial. New recruitment using revised eligibility criteria are currently being conducted to recruit male IDU’s with higher HIV-1 incidence. HIV-1 seroincidence is dynamic and affected by both treatment and prevention efforts. Continued efforts will be needed to monitor HIV-1 seroincidence in order to plan for efficacy trials.

George R. Seage III
Abt Associates Inc.
55 Wheeler Street,
Cambridge, MA 02138