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UNAIDS reports that 18.2 million people now receive lifesaving anti-HIV drugs.

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Young African women are especially vulnerable to HIV/AIDS

Young women in sub-Saharan Africa are living through a “particularly dangerous time” when it comes to risk of HIV infection, according to the annual World AIDS Day report of the Joint United Nations Programme on HIV/AIDS (UNAIDS) in Geneva, Switzerland. About 19% of the estimated 2.1 million new cases worldwide in 2015—the most recent data for most analyses in the report—occurred in women between the ages of 15 and 24. And younger women in some places are at far higher risk than men of the same age; in southern Africa, for example, 91% of new infections in the 15- to 19-year-old group were in adolescent girls. “Young women are in an age group that is the least likely to have taken an HIV test and know their status. It’s really amazing,” says UNAIDS Executive Director Michel Sidibé.

The reasons are complex, according to the report. Many young women do not perceive that they are at risk, and they live in what UNAIDS calls “challenging environments,” with insufficient access to food and education. In addition, many are involved in relationships with older men.

The new update for World AIDS Day, 1 December, offers a far more nuanced take on the epidemic than it has in previous years. For the first time, the report examines the disease in four age brackets that it calls “the life-cycle approach to HIV.” UNAIDS suggests this breakdown—0 to 14, 15 to 24, 25 to 49, and 50-plus—should lead to a clearer view of the epidemic’s “complex dynamics” and a more targeted response. One of the most surprising details is that Nigeria alone accounts for more than one-fourth of the 150,000 new infections in children last year. (Children are defined as 14 and younger; some of their infections occur during birth and some during breastfeeding.) Sidibé says he is “more disappointed than surprised” by the finding. “It’s a little bit our collective failure, including mine.”

Two factors underlie the problem in Nigeria, Sidibé says: little effort to focus resources on the regions of the country that have the biggest problems, and no strong “culture of accountability” to ensure funds are well spent. “I didn’t take the same bold approach I took in South Africa with Nigeria,” Sidibé says. “That should be my major new agenda.” In South Africa, more than 95% of HIV-infected pregnant women receive lifesaving antiretrovirals (ARVs), which also prevent mother-to-child transmission (MTCT). Nigeria is still analyzing its data, but UNAIDS told Science that the latest figures suggest that about 30% of HIV-infected pregnant women in that country were receiving ARVs.

Other trends are encouraging, according to the report. Roughly half, or 18.2 million, of the estimated 36.7 million HIV-infected people in the world have access to ARV treatment. New infections in children globally dropped 51% between 2010 and 2015, thanks to widespread programs to prevent MTCT. Annual AIDS-related deaths fell from 2 million in 2010 to 1.1 million.

In poor and rich countries alike, people are living longer with HIV/AIDS, thanks to effective ARV treatment. The oldest group of HIV-infected people, 50-plus years of age, is growing and now accounts for 17% of the total. And if treatment continues to become more widely available, as hoped, the number of HIV-infected people in this oldest age bracket could jump by 47% over the next 4 years.

But there’s grim news as well. The number of new infections in men and women between 25 and 49 years old has not changed. Not surprisingly, men who have sex with men, people who inject drugs, and sex workers accounted for 45% of the new infections in 2014. Although the risks are well known, “few countries and cities have mounted comprehensive responses for key populations,” which often face significant stigma and discrimination as well as laws that punish them for their behavior.

Funding remains an issue. Last year, roughly $19 billion was spent to combat HIV/AIDS in low- and middle-income countries, which are hardest hit by the epidemic, and just over half that money came from the countries’ own budgets. But UNAIDS says an additional $7 billion is needed each year to close gaps in prevention and treatment. “Reaching and sustaining this level of investment until 2030, and focusing these resources on delivering the most effective HIV services to the people in greatest need across the life cycle, will result in millions of additional lives saved and tens of millions of additional HIV infections averted,” the report concludes.