07/20/2015 06:12 EDT | Updated 07/20/2016 05:59 EDT

Key studies support case for starting HIV drug treatment right after diagnosis

TORONTO - Final results from two landmark studies have added more scientific weight to the case for starting HIV treatment immediately after diagnosis to help preserve an infected person's health and to prevent transmission of the virus to others.

The evidence of the two clinical trials presented Monday at the 8th International AIDS Society (IAS) conference on HIV Pathogenesis, Treatment and Prevention in Vancouver will play a significant role as the World Health Organization crafts updated HIV treatment guidelines, said Gottfried Hirnschall, director of the agency's HIV department.

In the START trial — for Strategic Timing of AntiRetroviral Treatment — almost 4,700 HIV-positive adults in 35 countries were randomized to receive either antiretroviral drugs soon after diagnosis or deferred treatment with the medications when the number of immune cells known as CD4s had dropped below a certain point.

The study was halted in May after interim results showed that immediate treatment cut the risk of serious illness or death from HIV-AIDS in half.

On Monday, co-principal investigator Dr. Jens Lundgren of the University of Copenhagen presented final data showing that early therapy not only lowers the risk of AIDS-related diseases, but also the risk of cancer, cardiovascular disease and other non-AIDS-related conditions in infected people.

"The data indicate that (early) treatment should be recommended for all HIV-positive people," Lundgren told a media briefing. "Of course the challenge now will be how to get the 20 (million) to 25 million people (worldwide) not on treatment yet, on treatment."

Ten-year results from the second major trial, known as HPTN 052, showed early treatment of an HIV-infected person dramatically reduces the risk of transmission to an uninfected partner.

The study involved 1,171 heterosexual couples in Africa, Thailand, Brazil and the United States. Infected participants were randomly assigned either to start antiretroviral drugs right away, while their immune system was relatively healthy, or to delay treatment until their immune system weakened or they developed an AIDS-defining illness.

Researchers reported Monday that starting antiretroviral therapy early reduced HIV transmission by 93 per cent over the course of the study. Only eight cases of transmission occurred in partners of infected participants who received antiretroviral therapy.

Four of those infections were diagnosed shortly after treatment began. In those cases, the virus most likely was transmitted just before antiretroviral therapy began or right after, before treatment had fully suppressed HIV replication. The other four infections occurred in study participants for whom treatment no longer was working and the virus was replicating.

Principal investigator Dr. Myron Cohen of the University of North Carolina at Chapel Hill said researchers did not observe transmission when the HIV-infected partner's virus was "stably suppressed on antiretroviral therapy."

"These findings illustrate that treatment is an incredibly powerful tool for HIV prevention," he said.

Also Monday, Dr. Robert Grant of the University of California at San Francisco presented findings from the ADAPT study, or Alternative Dosing to Augment Pre-Exposure Prophylaxis Pill Taking, that examined the feasibility of healthy people at high risk of infection taking an antiretroviral pill to prevent them becoming HIV-positive. The strategy is known as PrEP, or pre-exposure prophylaxis.

Researchers found that 76 per cent of young single black women in South Africa at high risk of infection adhered to the regimen of taking a daily pill.

Adherence to a daily pill was lowest among men who have sex with men and transgender women in Harlem, who stuck to the regimen only 65 per cent of the time. A similar group in Bangkok had the highest success with daily dosing, with 85 per cent taking the pills as instructed.

The study also looked at twice-weekly pills combined with one pill after sex, and a schedule that involved one pill before and one after sex. However, there were challenges in adhering to non-daily dosing, and it is not known yet if these regimens work to prevent HIV infection.

"This is an important step forward for optimizing HIV prevention strategies for people who would otherwise be at high risk for acquiring HIV infection," said Grant, who chaired the study.

"The findings will inform the next generation of PrEP research and the development of best practices regarding PrEP adherence and counselling."

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