William Smith is Vice President for Public Policy at the Sexuality Information and Education Council of the United States.

For advocates of evidence-based prevention, the International AIDS Conference in Toronto is likely to be remembered as a turning point in our efforts to eradicate HIV/AIDS. From the high-profile attention given to efforts such as microbicides, pre-exposure prophylaxis, male circumcision and harm reduction, prevention has come back to the fore and taken a seat alongside care and treatment, restoring the necessary balance to the global effort. Perhaps most interesting however, has been the repudiation at this conference of the lop-sided prevention efforts that have been focused on abstinence and marriage promotion.

In part, the repudiation has been made easy because the usual promotional tour for these issues has yet to manifest itself in Toronto. In fact, for those of us in the U.S., the near total absence of our government here in Toronto is startling, considering the bill of goods on prevention that it was forcing on the world at the earlier Barcelona and Bangkok HIV/AIDS conferences. In fact, on Tuesday night at an event hosted by The Lancet, Mark Dybul, head of the Office of the Global AIDS Coordinator, told the audience that he believes the focus of prevention is moving toward a firm foundation in evidence. Really.

That is encouraging news from the world's largest donor, but experience suggests a "wait and see" approach. However, if we had followed a public health approach based on sound evidence, instead of letting ideology lead us astray, PEPFAR's promise would have been even more fully realized. In the United States, we have had a quarter-century of experience (and more than $1 billion spent) that has shown us that abstinence-only-until-marriage programs are not sufficient and in fact, if young people are left to dwell in a vacuum without more comprehensive information, they make poorer decisions about protecting their health. As a result, Ambassador Dybul saying we are moving toward evidence seems to assume that the evidence wasn't there at the outset of PEPFAR. This simply isn't true. It was there, but it was jettisoned in some cases and twisted in others to justify a pre-determined approach that public health had already deemed a failure in our own country.

Some epidemiologists whom I respect immensely have come to regard abstinence and marriage promotion as "overhead" for getting PEPFAR's money where it is needed. That is the wrong diagnosis and all evidence from the US and countries where PEPFAR's more harmful policies are taking hold indicate that it isn't "overhead" – it is a Trojan horse with ominous and long-term implications for undoing the entire framework of preventing the sexual transmission of HIV, including supportive public policies.

Reauthorization of PEPFAR is on the horizon and if the United States continues to believe that it can better distribute funding than coordinated, multi-lateral efforts like the Global Fund, its glaringly obvious problems must be stripped – beginning with the abstinence-until-marriage earmark and the prostitution pledge. Countries need maximum flexibility in crafting and implementing efforts to meet the varied needs of the epidemics in their countries and waivers from silly, ideological hurdles are a cop-out from fessing up to flawed policies.

Enormous work remains to undo the damage that has been done and move forward. Yet, if Toronto is a turning point on this issue, it is because at home and abroad, advocates have sided with evidence – and bolstered their advocacy with a human rights framework and a desire for gender equity – that has restored evidence – not ideology – as the primary guide for prevention.