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Put the brakes on the world’s biggest pandemic: HIV/AIDS.

HIV/AIDS remains a huge public health menace, especially in sub-Saharan Africa, Russia, and former Soviet republics like Kazakhstan. Measures to slow the spread of the disease include campaigns to encourage use of condoms, especially among at-risk populations, and expanded testing so that more people know their HIV status. David Holtgrave, chairman of the Bloomberg School’s Department of Health, Behavior, and Society, notes that even in the United States, which has a sophisticated health information system, only 79 percent of people who are HIV-positive know it.

Holtgrave cites data that indicate the effectiveness of efforts in the United States to halt the transmission of HIV—including a 2006 transmission rate of under 5.0, which means that more than 95 percent of HIV-positive people in the States are not transmitting the virus. He also notes that the United States has nearly eliminated perinatal infection, made its blood supply safe, and reduced transmission among injection-drug users.

But globally, the search for effective HIV prevention has been less encouraging. David Celentano, professor of epidemiology, is skeptical of the effectiveness of most interventions, despite DCPP’s enthusiasm. He runs down a list of interventions that randomized clinical trials indicate are not doing the job: HIV prophylactic vaccines, “not working”; female-controlled microbicides that do not require male participation, “so far, nothing’s working”; prophylaxis by female diaphragm, “a complete failure”; behavioral interventions, “three major trials reported out in the last two years, all of which have shown no effect.” Celentano says there have been two modest successes. The first is male circumcision. Three large trials have produced strong evidence that circumcision can prevent HIV acquisition. The other success has been in preventing mother-to-child transmission. Researchers have used two drugs, AZT and Nevirapine, to cut the transmission from HIV-positive mothers to their newborns from 25 percent of live births to about 2 percent.

Celentano suspects that in the case of HIV/AIDS interventions, randomized clinical trials may not produce meaningful data. He points out that the people in control groups end up getting counseling and health care, too, and that may be enough to improve their health to the point that they are no longer valid as members of control groups. He wonders if, as a result, some interventions have worked better than the trials would indicate. Nevertheless, he points out that HIV/AIDS is particularly tough to deal with as a public health issue. “The major problem with most of the prevention programs we’ve seen is that you’re asking people to do something [like use a condom] all the time,” he says. “Virtually none of us can do something all the time. How many times a week do you not floss? How many women taking oral contraceptives realize, ‘I forgot to take my pill.’ As humans, we constantly fail.”

Repel malaria-carrying mosquitoes with bed nets.

In a typical year, about 1 million children die of malaria-related anemia, brain damage, and other complications. When the Kenyan government six years ago initiated a campaign that increased tenfold the number of children sleeping under insecticide-treated mosquito nets, mortality from malaria among those children was 44 percent lower than among unprotected children. The Global Health Council estimates the cost at about five bucks per kid, though Matthew Lynch of the Bloomberg School’s Center for Communication Programs pegs the cost, after the expense of transport, campaigns to support effective use, and distribution, at more like $10.

Treated nets work but can be problematic. They’re easily torn, which allows mosquitoes to get inside, and the insecticide’s effectiveness wears off in a few years, so the nets have to be replaced regularly. Sustained distribution of fresh nets is a constant challenge, and with malaria, if you back off, the disease comes right back. “The classic example is Sri Lanka,” Lynch says. “In the 1930s, more than 20,000 people died in an epidemic. The Sri Lankan government did this huge indoor residual spray campaign [using DDT] and got the deaths down to 18 in 1963. But within a year or two, the government said, ‘Why are we spending all this money on a disease that kills only 18 people?’ and stopped. By 1969, there were 520,000 malaria cases and 220 people died. We’ve seen this cycle before.”

Illustrations by Michael Gibbs