AEGiS-13IAC: Rapid decline in risk of HIV-1 acquisition after enrollment in a vaccine preparedness cohort of Kenyan prostitutes: implications for the design of HIV-1 vaccine efficacy trials.

13th International AIDS Conference

Durban, South Africa - July 9-July 14, 2000

Rapid decline in risk of HIV-1 acquisition after enrollment in a vaccine preparedness cohort of Kenyan prostitutes: implications for the design of HIV-1 vaccine efficacy trials.

Int Conf AIDS 2000 Jul 9-14; 13:(abstract no. MoOrC128)

Baeten J, Richardson B, Martin H, Nyange P, Lavreys L, Ngugi E, Mandaliya K, Bwayo J, Kreiss J
J. Baeten, University of Washington, PO Box 91276, Mombasa, Kenya, Tel.: +254 11 226 249, Fax: +254 11 474 055, E-mail: jbaeten@u.washington.edu

BACKGROUND: In designing HIV-1 vaccine efficacy trials, it will be important to account for changes in HIV-1 incidence, especially changes over time and while participating in risk-reduction programs.

METHODS: Data from an open cohort of female prostitutes in Mombasa, Kenya were analyzed. Individuals were censored after 3 years of follow-up or at HIV-1 seroconversion. Models of HIV-1 and sexually transmitted disease incidence and sexual risk behaviors over time were constructed using generalized estimating equations. Annual HIV-1 incidence for the entire cohort was calculated.

RESULTS: The risk of HIV-1 infection declined 10-fold during 3 years of follow-up (from 17.4 to 1.7 cases per 100 person-years for the first and last six months of follow-up, respectively, p>0.001). The incidence of gonorrhea, chlamydia, and genital ulcer disease each fell by half, and significant reductions in high-risk sexual behavior were observed. Fifty-seven percent of HIV-1 seroconversions occurred within 6 months of enrollment, and 73% occurred within 1 year. Despite on-going recruitment and evidence of increasing HIV-1 transmission in the community, accumulation of low-risk individuals led to a significant decline in HIV-1 incidence in the cohort as a whole during the first 4 years of the study (17.1, 11.5, 13.8, and 9.1 cases per 100 person-years during years 1, 2, 3, and 4, respectively, p>0.001).

CONCLUSIONS: This study documents a dramatic decline in the risk HIV-1 infection while participating in a prospective observational cohort, with most seroconversions occurring within one year of enrollment. Failure to anticipate variations in HIV-1 incidence within high-risk populations will result in HIV-1 vaccine trials with insufficient numbers of seroconversions to demonstrate protection from HIV-1 infection by efficacious vaccines.

Keywords: AEGIS, AIDS Vaccines, HIV-1, Prostitution, HIV Infections, Incidence, Sexually Transmitted Diseases, HIV Seropositivity, Sex Behavior, Gonorrhea, Kenya, Female, Epidemiology
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