"The work simply isn't done," incoming International Aids Society (IAS) president Linda-Gail Bekker told thousands of delegates at a closing ceremony.
"During the five days of this conference, 15,000 people living with HIV have died... And more than 28,000 have been newly infected with HIV, of which 1,500 were young people from this country alone.
"This makes me outraged and appalled and I see no room for complacency."
But as the number of new infections has levelled off, funding has dipped.
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A UNAIDS and Kaiser Family Foundation study presented at the conference this week pointed to a billion dollar drop in donor government funding, from USD 8.6 billion in 2014 to USD 7.5 billion last year.
"We're at a particularly critical moment for the future of funding," said Bekker, who is the first African women to lead the IAS.
Founded in 2002, the fund was established to raise money in the fight against Aids, malaria and tuberculosis.
The Fund is asking for at least $13 billion from donor governments.
Failing to address the funding gap, would only cost more money, said the Global Fund Advocates Network earlier this week.
A study released by the group this week warned of 21 million preventable Aids deaths and 28 million new HIV infections over the next six years if the Global Fund did not get the requested USD 13 billion.