To Combat AIDS, Help the Few to Save the Many


With Congress seriously considering a historic escalation in the global battle against AIDS, nobody seems to want to talk about a profound ethical dilemma: How should the money be spent?

With a stunning 8,000 new HIV infections a day, doing something is clearly a moral imperative. AIDS activists and public-health workers advocate increasing the distribution of condoms to stop the disease’s spread and making drugs widely available to help the victims. And on Capitol Hill, a coalition is forming around AIDS as a children’s issue, with politicians across the ideological spectrum supporting the distribution of drugs that prevent mothers from passing AIDS to their unborn children.

Yet, in the campaign to eradicate the worst plague of the modern era, all these approaches are common-sensical, compassionate--and doomed. The insights of a burgeoning field of science--the theory of networks--combined with hard lessons from the front lines suggest that the best hope lies in helping the promiscuous few, not the heart-rending many.


Decades of epidemiological studies have assumed that viruses spread on a social network in which individuals randomly interact with each other. In the past few years, though, we have learned that networks are far from random.

My research group, studying the World Wide Web, discovered that it has a peculiar, nonrandom structure: A few popular hubs, such as Yahoo or Google, link many small Web pages together. In the broader world, the same pattern repeats itself. A few key molecules in our cell’s complex chemical web interact with a staggering number of other molecules to keep us alive.

A handful of large corporations--the economic hubs that have financial ties to thousands of other companies--dominate our economy.

Hubs, it turns out, are what make networks so resilient.

These discoveries have profound implications for understanding how AIDS spreads and how to stop it.

Recently, a team of Swedish and American scientists mapped a network of sexual contacts, a kind of “sex web.” They found the same kind of hub structure seen in other networks; although most people have one to 10 sexual partners during their lifetime, a few individuals, such as Wilt Chamberlain, collect thousands.

At the same time, Italian theorists have offered a shocking prediction: In networks dominated by hubs, even a disease like AIDS--which is not highly infectious--will persist and spread.


Hubs play a key role in spreading a virus: They are likely to become infected because of their many sexual contacts and, once infected, are likely to spread it to many people.

While the use of condoms may save the individual, they will never eradicate the epidemic. Nor will drugs, if not given to all.

Given limited resources, the unique role of the hubs suggests a bold but cruel solution: When there is not enough money to help everybody who needs it, we should primarily give it to the hubs. Indeed, if we identify and help all the individuals who have many potential sexual partners, the number of newly infected cases will drastically decrease. The more hubs we target, the higher the chance that the epidemic will die out.

An effective AIDS policy requires more than money for drugs. We need the resources to quickly identify the hubs, and then we must have the mandate to single them out. Epidemiologists have long known the important role that prostitutes play in spreading sexually transmitted diseases. What the new science of networks is telling us is that any AIDS policy that ignores them is destined to fail.

Such a policy that targets individuals, of course, raises important ethical questions. Should society “reward” promiscuity? But with so many people dying every day, the real question is this: What is the best way to save the most people?


Albert-Laszlo Barabasi, a physics professor at the University of Notre Dame, is the author of “Linked: The New Science of Networks” (Perseus, 2002).