Speaking on Monday at a UN session to mark International Women's Day attended by Queen Noor of Jordan, Annan said girls and young women now account for nearly two-thirds of people worldwide under 24 who are living with HIV, the virus that causes Aids.
At least half of all new infections are women, which he said indicated a "terrifying pattern" that has changed the way the disease is cutting its way through communities across the globe.
"All over the world, women are increasingly bearing the brunt of the epidemic," Annan said. "If these rates of infection continue, women will soon become the majority of the global total of people infected."
He stressed that the strategy of trying to combat the illness through abstinence and the use of condoms was not "realistic" for many women, whom he said are suffering because of their inferior status in many societies.
"If these rates of infection continue, women will soon become the majority of the global total of people infected"
UN Secretary General
Why, he asked, are women more vulnerable to infection despite the fact that their male partners are more likely to be the ones engaged in at-risk behaviour?
"Usually because society's inequalities puts them at risk -unjust, unconscionable and untenable risk," Annan said. "There are many factors, including poverty, abuse and violence, lack of information, coercion by older men, and men having several partners," he said.
"Society pays, many times over, the deadly price of the impact on women of HIV/Aids."
Queen Noor: Women seldom
control their own sexual lives
Queen Noor, the widow of King Hussein, told the session that despite relatively low number of people living with the disease in the Middle East - an estimated 600,000 in the region - more than half of those were women.
"They bear children but seldom control their own sexual lives," she said.
Money and education
The head of the UN's Development Fund for Women, Noleen Heyzer, told reporters that women were vulnerable to the disease for a number of reasons, including a lack of both money and education.
She said that in many societies, women are getting married at an increasingly early age to try to improve their economic situations - and marrying increasingly older men, a point underlined by Annan.
In many societies, women are getting married at an increasingly early age to try to improve their economic situations - and marrying increasingly older men
"What is needed is real, positive change that will give more power and confidence to women and girls, and transform relations between women and men at all levels of society," the UN chief said.
He called for "change that will strengthen legal protection of women's property and inheritance rights... (and) change that makes men assume responsibility."