MRKAd5 Vaccine Found Ineffective Against HIV-1

Failed to protect against virus acquisition, decrease in viral load in South African study

MONDAY, May 16 (HealthDay News) -- A vaccine tested in a cohort of men and women in South Africa failed to prevent acquisition of HIV-1 or a decrease in viral load in those who acquired the virus, according to research published online May 12 in The Lancet Infectious Diseases.

Glenda E. Gray, M.B., B.Ch., of the University of Witwatersrand in South Africa, and colleagues randomly assigned 801 participants -- 360 of them women -- at five sites in South Africa to receive the MRKAd5 HIV-1 vaccine or placebo to test the safety and efficacy of the vaccine for protecting against disease acquisition or against decreasing viral load after acquisition.

In their modified intention-to-treat cohort, 34 subjects who received the vaccine acquired HIV, as did 28 individuals in the placebo group. The researchers found no evidence of vaccine efficacy. The geometric mean viral-load setpoint in the treatment group was 20,483 copies per mL, compared with 34,032 copies per mL in the placebo group (P = 0.39). Enrollment and vaccination in this study were halted when the Step study found the vaccine not efficacious.

"The MRKAd5 HIV-1 vaccine did not prevent HIV-1 infection or lower viral-load setpoint; however, stopping our trial early probably compromised our ability to draw conclusions. The high incidence rates noted in South Africa highlight the crucial need for intensified efforts to develop an efficacious vaccine," the authors write.

The trial was funded in part by Merck and Co. Inc.

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