My college roommate—the most immediately likable person I’ve ever met, a man who would now be such a present to the world—died of AIDS at the age of 30. Back then, people with the disease did not so much die as fade, becoming gaunt and ghostly images of themselves, as the virus gradually destroyed enough T-cells to cut their ties with the flesh. Metaphors don’t really capture the horror. Declined? Withered? At any rate, he died.

That was 20 World AIDS Days ago, shortly before the arrival of miracle drugs that could have saved my friend’s life. Several years later, when I was on the White House staff, the existence of those medicines created a serious moral dilemma. While antiretroviral drugs were broadly available in the developed world, they were rarely distributed elsewhere. Of about 30 million people with HIV in sub-Saharan Africa, perhaps 50,000 were on treatment. The pandemic had already produced 14 million orphans. Walking through South African shantytowns, I mainly met grandmothers and their grandchildren. The intervening generation was nearly erased. In the worst affected countries, life expectancy had fallen by 20 years.

President George W. Bush refused to live with this dilemma, urging the creation of the Global Fund to Fight AIDS, Tuberculosis and Malaria, then proposing a $15 billion emergency package of treatment, prevention and compassionate care (PEPFAR). A bipartisan congressional coalition supported this effort, which has been sustained across two administrations by the influence of tireless advocates inside and outside of government.

The global fight against AIDS was characterized, at first, mainly by breadth. After Bush’s announcement of PEPFAR in the 2003 State of the Union address, hospital tents were erected in some places to get as many people on treatment as quickly as possible. Over time, PEPFAR and the Global Fund strengthened an infrastructure of laboratories, supply chains, human resources and infection control programs. Nearly 7 million people are now receiving AIDS drugs with the help of PEPFAR. Life expectancies in Africa have dramatically rebounded. In 2013, for the first time, more people started on AIDS treatment than were infected by the virus. A milestone.

But the next stage of the AIDS response will tie ambition to precision. We are accustomed to the data revolution as the cause of civil libertarian concern and the seswwwource of annoyingly targeted advertising. But epidemiologists are following improved data to the specific sites where disease is spread.

“Whether Ebola, HIV or malaria, infectious disease epidemics are controlled by focusing where new infections are occurring,” Mark Dybul, executive director of the Global Fund, told me. “For example, in Kenya, 53 percent of new adult and 73 percent of new child HIV infections are from five of 47 counties. Rates are highest among fisher folk, young women who trade sex with them and MSM [men who have sex with men]. If we focus on high-level endemic locations and populations, we can bend the curve rapidly and move to bring the HIV epidemic under control.”

Disease experts now have a set of proven HIV prevention methods: early treatment, male circumcision, condoms and the prevention of mother-to-child transmission. They have increasingly specific data on the geographic regions where infections are concentrated. They have a good idea of the highest-risk and hardest-to-reach groups: MSM, transgender people, people who inject drugs, children (who get treatment at lower rates) and young women. (Gender-based violence remains a major problem. In Swaziland, for example, 43.5 percent of females 13 to 24 report unwilling first sexual intercourse prior to age 18.)

All this data allows scientists essentially to shrink the epidemic map. We already knew that 30 countries have 89 percent of new HIV infections. Now we know, for example, that 22 percent of HIV testing and counseling centers in Tanzania report 88 percent of total positives. Resources can be employed where they will make the most difference. And these gains could be decisive when paired with an even partially effective vaccine (which is now a realistic prospect).

As usual, politics can get in the way. The kind of politics that wants to distribute resources equally by region to keep the locals happy. The kind of politics that targets groups for stigma and discrimination, particularly MSM who are too frightened to seek health services.

 What is needed is compassion, increased resources, and data that shapes policy. And a memory of the lost — whose number still grows by nearly 30,000 each week.

(Washington Post Writers Group)