May 15, 2006 issue - A few months ago, on a trip to Africa, I met with a group of women in Kibera, the biggest slum in Kenya. These women ranged in age from 16 to 45 but had one thing in common: AIDS had devastated their lives. A woman I'll call Chanya told me her story. Chanya is a mother in her 30s trying to raise four children. She does not fit the typical profile of a person living with AIDS—at least not the profile that prevails in the West. She is not a man who has sex with men; she is not a sex worker; she does not use IV drugs. She has engaged in no behavior at all that is high risk for AIDS, except for one—she got married. Her husband, tragically, did engage in high-risk behavior: he had unprotected sex outside his marriage. After acquiring HIV, he passed it on to Chanya. She spoke in a hushed but matter-of-fact voice about her situation. "My husband died of AIDS. I knew we should use a third-leg sock," she told me, using the colloquial phrase for a condom, "but he refused. Now my children will be orphans."

Chanya's story is not rare. For many women, marriage is a risk factor for AIDS because of their husbands' dangerous behavior. Worldwide, 80 percent of women newly infected with HIV are practicing monogamy within a marriage or a long-term relationship. This shatters the myth that marriage is a natural refuge from AIDS. And it shows that, more than two decades into the epidemic, our fight against AIDS has failed to address the unique circumstances of women—especially women in the developing world.

Why are women so vulnerable? Physiological differences make women twice as likely as men to contract HIV from an infected partner during sex. In many countries, sexual inequality compounds the hazard by making it difficult, if not impossible, for women to enforce their choices about whom they have sex with, or to insist that men wear condoms. But one of the deadliest problems is that women simply don't have the tools to protect themselves. Despite the array of breakthroughs we've seen for AIDS treatment, prevention efforts still rely on the three practices described by the abbreviation ABC ("Abstain, be faithful, use condoms"). These approaches work, and we must encourage them, but they all depend on a man's cooperation. For millions of married women, abstinence is unrealistic, being faithful is insufficient and the use of condoms is not under their control.

Through our foundation, my husband, Bill, and I are working to develop tools that can put the power to prevent AIDS into the hands of women. Microbicides are one exciting new prevention tool in development. These are colorless, odorless gels that a woman could apply vaginally—without her partner's knowledge—to prevent sexual transmission of HIV. Microbicides may also prevent other sexually trans-mitted infections, such as syphilis and gonorrhea, and some act as contracep-tives as well. Microbicides are now being tested by women in several countries with large HIV burdens, including South Africa, Uganda and India. Researchers are also studying other promising measures that could give women the power to protect themselves with-out depending on their partners. For instance, trials in Botswana, Ghana and other countries are studying whether drugs now used to treat HIV may also protect people from being infected in the first place.

When we consider the millions of women who have died, it's tragic that the world has been so slow to invest in HIV-prevention tools that women can initiate. We know why so many women are get-ting infected and we know what we can do to stop it. Here are some of the steps needed to make the most of these lifesaving opportunities

First, governments in both developed and developing countries must commit more money to studying new prevention tools. Although funding increased from $65 million in 2000 to $163 million in 2005, current spending is only about half of what is needed to advance the most promising microbicide candidates. Pharmaceutical companies have little incentive to invest, because the women who most need these products can't afford to pay for them. But governments can encourage companies to get involved by providing direct funding for research, and by promising to purchase new technologies if they are successfully developed.

At the same time, developing countries, with international support, need to build the infrastructure to host clinical trials so that promising new tools can be tested in the settings where they'll be used. If developing countries can't run trials, lifesaving breakthroughs will sit in laboratories waiting to be tested. By some estimates, 100,000 people will be needed for HIV-prevention studies over the coming decade. Yet most of Africa's trial sites are now filled to capacity. Countries need to invest in more facilities, and train a new generation of doctors and nurses to run them.

The challenge is not just to develop new tools. We also need to ensure that scientific advances reach the people who need them. Today, fewer than 20 percent of people at high risk of HIV have access to existing prevention methods, such as condoms, education and HIV testing. Health ministries, NGOs and businesses must combine their resources and ingenuity to improve rapidly on that record.

Ten years ago, 1 percent of women in South Africa had contracted HIV; today the number is 25 percent. These women are living a nightmare, but we in rich countries are the ones who have to wake up. We need to develop prevention tools that can give women a chance to defend themselves. We need to deliver them as soon as they're available, and we need to deploy now the prevention tools we already have. Sadly, nothing can come fast enough for Chanya. But if we hurry, we can deliver these new advances in time to protect her children.

Gates is co-chair of the Bill & Melinda Gates Foundation. http://www.gatesfoundation.org/default.htm