Feasibility of a preventive HIV-1 vaccine cohort among persons attending sexually transmitted disease clinics in Thailand

Abstract

Persons attending sexually transmitted disease clinics at three sites in Thailand were recruited to participate in a 1-year study of HIV-1 incidence. Between September 1995 and February 1996, 31% (371 of 1205) of eligible men and 24% (161 of 659) of eligible women agreed to participate. At enrollment, HIV-1 seropositivity was 3.8% among men and 2.5% among women. Follow-up of the 514 participants who were seronegative at baseline was 78% at the 12-month visit. During the study period, 53% of men reported 2 or more sexual partners, 31% reported sex with a commercial sex worker (CSW), and 33% with a casual partner. Of those visiting CSWs, 72% reported consistent condom use. Among women, 11% reported 2 or more sexual partners. Decreased HIV risk behaviors among men were observed during the study. Four incident infections occurred in men (1.4/100 person-years, 95% confidence interval [CI] = 0.4-3.6) and none among women. Based on the observed HIV-1 incidence, HIV vaccine efficacy trials in such populations would have to be larger than previously planned or more selective of high risk subgroups for recruitment.

PIP: Thailand is one of the few countries in which plans for HIV-1 vaccine efficacy trials are proceeding. The determination of cohort sample size for such trials depends upon the HIV-1 incidence among those who may enroll in the trials, participant retention, trial duration, and the frequency of risk behavior during the trial. The authors conducted a prospective cohort study of sexually transmitted disease (STD) clinic attendees at 3 sites in Thailand to determine whether a cohort in the population would be suitable for future HIV-1 vaccine efficacy trials. Between September 1995 and February 1996, 371 of 1205 (31%) eligible men and 161 of 659 (24%) eligible women agreed to participate in a 1-year study of HIV-1 incidence. At enrollment, 3.8% of the men and 2.5% of the women were infected with HIV-1. Almost all women and 54% of the men were married at the time of enrollment. 78% of the 514 participants who were seronegative at baseline were still being followed at the 12-month visit. During the study period, 53% of men reported having 2 or more sex partners, 31% reported having sex with a prostitute, and 33% with a casual partner. 72% of those frequenting prostitutes reported consistent condom use. 11% of women reported 2 or more sex partners. Decreased HIV risk behaviors among men were observed during the study. 4 incident infections occurred in men and none among the women. Based upon this observed HIV-1 infection incidence, HIV vaccine efficacy trials in such populations would have to be larger than previously planned or more selective of high-risk subgroups for recruitment.