The United Nations Programme on HIV/Aids has called for increased funding for the early treatment of people with HIV.
UNAids head Michael Sidibe says a new study showed it could reduce the risk of HIV transmission by 96%.
He says the challenge is to expand access to drugs and deal with social factors which stigmatise the disease.
UNAids believes an investment of at least $US22 billion is needed by 2015, $US6 billion more than is available today. It estimates such funds would stop 12 million new HIV infections and 7.4 million Aids-related deaths by 2020.
In a report issued to mark 30 years since the first recorded case of AIDS, the agency said on Thursday that the rate of new infections has fallen by almost 25% over the past 10 years.
However, it also noted that there had been an increase in the rate of new HIV infections in Eastern Europe and in the Middle East and North Africa.
The UN says an estimated 34 million people were living with HIV at the end of 2010. Nearly 30 million have died from Aids-related causes since 1981.