New findings from a study of 888 mixed-HIV-status couples —both gay and straight—saw no transmissions within the couples, further underlining the power of antiretrovirals (ARVs) to curb the spread of the virus.

The analysis focused on periods when couples reported ongoing condomless sex—a total of 58,000 times—and the HIV-positive partner had an undetectable viral load. These couples were followed for a median 1.3 years.

Eleven participants contracted HIV during the follow-up period, including 10 gay partners and one heterosexual partner. Genetic analyses found that none of these transmissions came from the individuals’ primary partner.

The researchers have categorized the risk of transmission among heterosexual couples as “extremely low” when the HIV-positive partner has a fully suppressed viral load for several months and is adherent to an ARV regimen. The investigators need to follow the gay couples longer before they can downgrade their risk from the current assessment of “very low” to “extremely low”—provided, that is, that there are no transmissions among them in the context of full viral suppression.

“In general, our study does not intend to say to people what they should do regarding condoms but rather inform couples of the risks in order for them to make an informed decision,” says the study’s lead author, Alison Rodger, MD, an infectious disease specialist at University College London. “Everyone has a different tolerance of risk no matter how small that risk may be.”