Healthy HIV-free people could reduce HIV transmission risks if they take a daily dose of antiretroviral drugs used to treat it, two groundbreaking studies have found.

A new study from the Centers for Disease Control and Prevention, or CDC, called the TDF2 Study, gives evidence that a daily oral dose of antiretroviral drugs can reduce the risk of uninfected people getting the virus through heterosexual sex.

The CDC conducted the study with the Botswana Ministry of health. In the study they found that a once-daily tablet containing Truvada can lower the risk of getting the HIV infection by about 63 percent.

Similarly, in a Partners PrEP study, the University of Washington has found that daily pre-exposure prophylaxis, or PrEP, also reduces HIV transmission among heterosexual couples in Kenya and Uganda. PrEP is the strategy of providing daily oral antiretroviral drugs to uninfected people prior to the being exposed to HIV.

The PrEP study provided evidence that two separate antiretroviral regimens namely tenofovir, commonly called Viread, and Truvada, significantly reduced HIV transmission among couples where one partner is infected with HIV and the other is not.

These discoveries could change the approach to HIV prevention.

These are exciting results for global HIV prevention. We now have findings from two studies showing that PrEP can work for heterosexuals, the population hardest hit by HIV worldwide, said Dr. Kevin Fenton, director of CDC's National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, in a press release. Taken together, these studies provide strong evidence of the power of this prevention strategy.

The CDC study included 1,219 HIV-uninfected heterosexual participants, both men and women between ages 18 and 39, in Botswana. They were enrolled in the trial and were randomly assigned to take a daily dose containing Truvada or a placebo pill.

The CDC said all the participants were given comprehensive HIV prevention services to include male and female condoms. The also got intensive risk-reduction behavioral counseling and testing and treatment for sexually transmitted infections.

Three participants were determined to be HIV-infected at the time of enrollment. Sixteen randomized participants began study medication, and were excluded from the analysis. The CDC said the analysis only included data on the remaining 1,200 participants who were HIV-negative at the time of enrollment and began study medication, which were 54.7 percent male and 45.3 percent female.

Among the 601 participants who received Truvada, nine became infected with HIV during the study.  As for the 599 people who got a placebo, 24 became infected with HIV during the study, the CDC found.

Given the severity of the HIV epidemic among heterosexual men and women globally - and the critical need for female-controlled prevention methods - this study provides exciting and welcome news, said Dr. Jonathan Mermin, director of CDC's Division of HIV/AIDS Prevention.  The next important step is to fully review the data and assess when and how PrEP should best be used for HIV prevention among heterosexuals.

The University of Washington's study was led by International Clinical Research Center and was funded by the Bill & Melinda gates Foundation.

It involved 4,758 HIV couples where one partner has HIV and the other does not from nine research sites in Kenya and Uganda.

This study is the largest study to date looking at the effectiveness of PrEP, said Dr. Connie Celum, a university of Washington professor of global health and medicine and the principal investigator of the study. This study demonstrates that antiretrovirals are a highly potent and fundamental cornerstone for HIV prevention and should become an integral part of global efforts for HIV prevention.

Of the 4,758 couples enrolled in that study, a third of the HIV uninfected partners were randomly allocated to be given tenofovir; another third was given tenofovir combined with emtricitabine; and the other third was given matching placebo.

Participants in this study also got comprehensive HIV prevention services.

The study found that those who received tenofovir had an average of 62 percent fewer HIV infections; those who got tenofovir combined with emtricitabine had 73 percent fewer HIV infections than those who got placebo.

This is an extremely exciting finding for the field of HIV prevention. Now, more than ever, the priority for HIV prevention research must be on how to deliver successful prevention strategies, like PrEP, to populations in greatest need, said Dr. Jared Baeten, co-chair of the study and a University of Washington associate professor of global health and medicine in a statement.