Joao Silva for The New York Times
Volunteers who took part in a trial of a microbicide listened to results in Vulindlela, Kwazulu-Natal Province, South Africa.
JOHANNESBURG — When scientists celebrated the announcement in July that a vaginal microbicide had finally been found that significantly reduced H.I.V. infections in women, there was still a prosaic — though essential — piece of the puzzle missing: money.
Donors have not committed enough money for even one of the two studies needed to confirm a promising South African trial of the microbicide and get it into women’s hands. Only about $58 million of the $100 million needed for follow-up research has been pledged, according to Unaids, the United Nations AIDS agency. Experts say shifting global health priorities and tight finances in the West are making it hard to raise the rest.
Advocates say any delay could be deadly. Most of the 22 million people infected with H.I.V. in sub-Saharan Africa are women, and about a million women on the continent are infected each year. If subsequent studies find the gel effective, women could use it to protect themselves even when men refuse to use condoms.
“We have to keep our eye on the prize,” said Dr. Catherine Hankins, chief scientific adviser to Unaids. “It’s in reach. We have to close the funding gap and get the gel to women.”
Dozens of scientists and public health experts at a conference here last week agreed on the research needed to speed the microbicide to widespread use. They called for two more trials in southern Africa and steps to promote and distribute the vaginal gel, infused with the antiviral drug tenofovir, through family planning programs.
The original study of the gel found that women who used it before and after sex were 39 percent less likely over all to contract H.I.V. than those who used a placebo. Those who used the gel most regularly cut their odds of infection by 54 percent.
Researchers have tried for two decades to find a microbicide to fight H.I.V. transmission. So far, the American and South African governments have come up with a vast majority of the additional research money, while Britain’s Department for International Development, a major supporter of microbicide research, has committed nothing.
Participants in the conference said an agency official said the British government’s priorities were shifting away from AIDS and toward maternal and child health, malaria and tuberculosis.
“H.I.V./AIDS is perceived to be very expensive research, and there’s a sentiment in the U.K. that it’s time to shift priorities,” said Tim Farley, a World Health Organization scientist who attended the conference.
The British agency was noncommittal in a statement, saying that future spending “will be made based on impact on poverty eradication on the ground.”
Researchers also worry that the Bill and Melinda Gates Foundation, the most important philanthropic supporter, has not committed major financing for the additional studies on the gel. Dr. Stefano Bertozzi, who heads the foundation’s AIDS programs, said the gel — with a solid study showing its effectiveness — was just the kind of project that rich countries could justify to taxpayers. “It should be an easy case for South Africa, ourselves and others to make,” Dr. Bertozzi said.
He said the foundation was excited about the results, but tried to focus on riskier, longer-term research. The foundation has committed more than $250 million to microbicide research.
The hope is that two additional studies would provide the evidence to adopt the gel on a large scale. Three rigorous studies have established that male circumcision reduces a man’s risk of H.I.V. infection by at least half, and governments across Africa are beginning to offer it.
For the microbicide, researchers plan to lead one of the confirmatory studies in South Africa, where an estimated 5.7 million people are infected, more than in any other nation. Scientists would conduct the second study in five southern African nations.
Experts say investing in AIDS prevention is fiscally far preferable to the costs for lifelong treatment. Mead Over, a health economist at the Center for Global Development, says that providing antiretroviral therapy to the five million people with AIDS in Africa already receiving it will cost $72 billion over the next four decades. That amount rises to $225 billion if the number of people on treatment continues to grow.
“Donors should not be nickel and diming this research because by spending only $100 million they have a prospect of saving billions of dollars in treatment costs,” Mr. Over said.
Advocates make the case on humanitarian grounds.
“We see every day women getting infected by H.I.V.,” said Nomfundo Eland of the Treatment Action Campaign, an advocacy group here. “The sooner we can get a method in the control of women the better.”