There is no room for sexual morality in an honest conversation about Aids

When scientists first identified the HIV virus in 1984, they expected to have a vaccine in two years. Twenty-three years later, we are still waiting. Meanwhile various partially effective means of prevention have been developed. Consistent condom use reduces the likelihood of HIV transmission, as does male circumcision, in those with the condition. But people seldom use condoms consistently, and male circumcision is still rare in the most highly Aids-affected countries.

What can be done? One thing that we can do is explore what happened in places where the epidemic did turn around. I've been thinking about this for nearly 15 years, and it's become increasingly clear to me that the key to fighting Aids lies in something for which public health has no name or programme. It is best described as a sense of solidarity, compassion and mutual aid that is impossible to quantify or measure. It has to be this way. Because our sexuality is shaped by society and because sex itself involves more than one person, behaviour change is a collective act, not one of individuals acting alone. That's the reason why social mobilisation is so important. And that's also why HIV prevention is so difficult.

But sometimes it works. Almost as soon as the first bulletins about a new disease affecting homosexual men appeared in US newspapers in 1981, the entire gay community rose up against it. Gays argued about bathhouses and condoms; they chained themselves to government buildings to protest official inaction; they nursed their dying friends. If you visit the Aids section of any library, you'll find a wall of literature from that time: poems, plays, memoirs, art books, philosophical essays. It was like a mass conversation. During this period, a huge shift in sexual norms occurred, and the incidence of HIV infection fell by about 80%.

Something similar happened in Uganda when the HIV rate there plummeted by about 70% during the 1990s. I worked in Uganda at that time, and I remember thinking that the epidemic might have been different from the gay epidemic, but the response was remarkably similar. There were plays, vigils and marches, and everyone talked about Aids in highly personal ways. There was vigorous public debate about condoms and about how men and women treated one another. For historical reasons, Uganda had a vibrant women's movement, and Aids fitted right into their agenda too. People cared for the sick and their orphaned children. Some were supported by donors and churches, but most simply volunteered. As one man who remembers this time explained to me: "You'd go over, take care of the kids, sweep the floor, just sit and talk to the patient; you couldn't just do nothing."

We'll never know why people in other African countries did not respond to Aids in this way, but, for a while, I've wondered whether it didn't have something to do with the fact that Ugandans - like gay men - knew where their risks were coming from, and this enabled a more open, pragmatic response.

In 1986, long before rich donors such as the US government and the UN came on the scene, Ugandan health officials designed their own HIV prevention programme. It was based on a crucial epidemiological insight that has, until recently, eluded most outsiders working on Aids in Africa: HIV rates are high in this region not because people have so many sexual partners, but because they are more likely than people elsewhere to have more than one - perhaps two or three - long-term partners at a time. This "long-term concurrency" differs from the "serial monogamy" more common in western countries, and the casual and commercial sexual encounters that occur everywhere. But long-term concurrent relationships are far more dangerous, because they link people into a giant network that creates a superhighway for HIV.

Uganda's original Aids campaign had two main messages. First, "zero grazing" - local slang, meaning roughly, "try to stick to one partner, but at least avoid casual partners, and cut down on concurrent partners if you can". And second, everyone is at risk, not just prostitutes, truckers and other so-called promiscuous people.

What was going on in the rest of Africa? One thing I have noticed is how many Aids campaigns elsewhere suggest that people with Aids are "promiscuous". When I was visiting Botswana a couple of years ago, a US government-funded campaign to promote condoms was under way. Like many such campaigns, it had a ribald, sexy tone. I remember one poster of a boxing glove, a condom and the slogan "It can take the fiercest punches". The ad reflected the prevailing view among epidemiologists at the time, that HIV was spread by "high risk groups" - meaning, typically, promiscuous people.

This was true in most of the rest of the world, but not in Botswana. The boxing glove ad and others like it may have promoted a false sense of security, and by associating HIV with womanising and violence, the ads may also have unintentionally reinforced the shame and denial that has made Aids prevention in southern Africa so difficult.

In 1992, foreign donors phased out Uganda's zero grazing campaign and replaced it with a programme emphasising condom use for "people at high risk" similar to those in the rest of the region. But a few years ago, officials began to worry because although the HIV infection rate had fallen rapidly in the 1990s, the decline had ceased by the end of the decade. But instead of reviving the zero grazing campaign, the officials, with support from the Bush administration, mounted an "abstinence" campaign, which ironically sent a message very similar to the condom ads: only immoral people get Aids. To everyone's horror, the HIV rate in Uganda is beginning to rise again.

People always ask me: "So, fighting Aids requires a social movement. How do you generate a social movement?" Well, one thing that always galvanises people is a common enemy. Too many donor funded Aids programmes have divided people: HIV-positive from HIV-negative, "moral" from "immoral", high-risk from low-risk. Such programmes send the message that the enemy is people with Aids. Ugandans and gay men knew early that the enemy was HIV itself.

Helen Epstein