Longini I, Kitayaporn D, Vanichseni S, Choopanya K, Hudgens MG, Halloran ME, Mastro TD, Mock PA; International Conference on AIDS.

Int Conf AIDS. 1998; 12: 955 (abstract no. 43552).

Dept. Biostat., Rollins School Pub. Health, Emory Univ., Atlanta, GA 30322, USA.

BACKGROUND: Prophylactic HIV vaccines could reduce susceptibility to infection or disease, i.e., vaccine efficacy for susceptibility (VEs). They also may reduce infectiousness of vaccinees who become infected, i.e., vaccine efficacy for infectiousness (VEi). This latter effect could produce an important indirect reduction in HIV transmission even if the vaccine does not protect well against infection. We propose an augmented design for HIV vaccine trials that allows estimation of both effects. The augmented design includes steady sexual partners of primary participants. METHODS: A placebo-controlled phase III HIV vaccine trial is simulated according to the structure of the Bangkok Metropolitan Administration (BMA) cohort of injecting drug users. In the simulation, 1,250 primary participants are recruited per arm. Participants and their steady sexual partners are followed every six months for three years. Primary participants are assumed to be at risk of infection through needle-sharing at various frequencies. In addition, 50% of the primary participants have unprotected sexual contact with a steady partner at various frequencies. A likelihood function based on a Markov model is used to estimate the VES and VEi. RESULTS: In the simulated baseline vaccine trial, cumulative incidence in the placebo arm among primary participants is 12% for the entire trial. There are 119 total infections in the placebo arm. The secondary attack rate (SAR) among sexual partners in the placebo arm is 46%. The VEs and VEi were preset to 0.4 and 0.6, respectively. The estimated 95% confidence interval (CI) on VEs is [0.22, 0.56] and on VEi is [0.37, 0.74]. The power to reject H0: VEs = 0 and H0: VEi = 0 is 1.0 for both. If the HIV incidence rate is reduced so that 92 infections occur among primary participants in the placebo arm and SAR = 32%, then the estimated 95% confidence interval on VEs is [0.23, 0.54] and on VEi is [0.31, 0.78]. The power to reject H0: VEs = 0 and H0: VEi = 0 is still 1.0 for both. CONCLUSIONS: It should be feasible to estimate both VEs and VEi for vaccine trials in developing countries that have populations where the primary participants are exposed to infection through injecting drugs or sexual contact, and who have steady sexual partners. Several populations, in addition to the BMA cohort, with this social structure are being considered for HIV vaccine trials.

Publication Types:

• Meeting Abstracts

Keywords:

• AIDS Vaccines
• Acquired Immunodeficiency Syndrome
• Clinical Trials as Topic
• Clinical Trials, Phase III as Topic
• Confidence Intervals
• Developing Countries
• HIV Infections
• HIV Seropositivity
• Incidence
• Likelihood Functions
• Placebos
• Sexual Partners
• Substance Abuse, Intravenous
• Thailand

Other ID:

• 98405180

UI: 102231715

From Meeting Abstracts