Addressing 20,000 AIDS scientists, health workers and activists at an international conference in Vienna, the former U.S. President and the Microsoft founder said efficiency savings were vital in delivering HIV/AIDS prevention services and treatment to the countries hardest hit and at highest risk.

The world is awash in troubles. It is easy to rail at a government and say ... give us more money. But we also have to change the way we do what we do, Clinton told the conference.

If we're going to make this case, they (donor governments) have to believe that we are doing our job faster, better and cheaper. Then we have the moral standing to go ask people to give us more money.

Gates, a philanthropist whose Gates Foundation spends a large portion of its $34 billion fund on fighting AIDS, said efficiency was vital to be able to scale up access to AIDS drugs for the 15 million people who need them.

We can't keep spending AIDS resources in exactly the same way we do today, he said. As we ... advocate for more funding, we also need to make sure we're getting the most benefit from each dollar of AIDS funding and every ounce of effort.

The head of the Global Fund to Fight Aids, Tuberculosis and Malaria says it needs $20 billion in the next three years to sustain progress in tackling the diseases.

Out of the 33.4 million people who are infected with the human immunodeficiency virus HIV that causes AIDS, 5.2 million now get the drugs they need. But non-drug-related costs of treatment, such as hospital costs, labs, testing and monitoring, are more than twice the cost of the medicines.

Gates called for rapid scale-up of cheap, effective, and easy to apply HIV/AIDS prevention measures -- such as male circumcision and prevention of mother-to-child transmission of HIV -- which he said were so cost-effective that in endemic countries it is more expensive not to pursue them.

Yet in the case of male circumcision, while more than 41 million men in sub-Saharan Africa could benefit from it, only 150,000 have been circumcised in the past few years, Gates said.

Both Gates and Clinton also cited new studies showing that treating HIV patients with cocktails of AIDS drugs can dramatically reduce transmission of the virus to others.

Clinton's whose William Clinton Foundation also works in the fight against AIDS, warned activists not to battle with President Barack Obama's administration or other governments who he said were essentially on their side.

Hundreds of protestors marched through the Vienna conference on its opening day on Sunday to demonstrate against a pullback of funding for AIDS in the wake of a global recession.

Clinton said the campaigners should recognize Obama as their friend, and seek to work with him not against him.

You have two options here, you can demonstrate and call the president names, or we can go get some more votes in (the U.S.) Congress to get some more money, Clinton said. My experience is that the second choice is a better one and far likelier to pay off. There is no way the White House will veto an increase in funding for AIDS.

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