According to a new study, when the HIV-negative partner in a mixed-HIV-status heterosexual couple takes Truvada (tenofovir/emtricitabine) as pre-exposure prophylaxis (PrEP), this provides a highly effective “bridge” to preventing infection until the HIV-positive partner starts antiretroviral (ARV) treatment and reaches an undetectable viral load.

“Our results show that when given access to PrEP, couples wanted it and used it and garnered extremely high benefits from it,” says Jared Baeten, MD, PhD, a professor of global health at the University of Washington in Seattle and the head of the Partners Demonstration Project, which is an ongoing trial of 1,013 mixed-status heterosexual couples in Kenya and Uganda.

The HIV-negative partners were offered PrEP until the HIV-positive partners, none of whom had been treated before, had opted to begin ARVs and been on them for six months. The researchers compared their results with data from the group that took a placebo instead of Truvada in a previous study of mixed-status couples, called Partners PrEP. That study’s findings suggested that, without ARVs or PrEP, there would be an average of 5.2 transmissions per year for each 100 couples.

The Partners Demonstration Project saw only two transmissions during their study period, or 0.2 transmissions per year for each 100 couples. This means that the PrEP bridge and ARV treatment together lowered the risk of transmission by an estimated 96 percent. For those who actually adhered to the protocol, its protective effect appeared even higher, since both individuals who tested HIV positive had apparently stopped taking PrEP.