The Aids epidemic is wreaking havoc on all parts of society in sub-Saharan Africa. Yet, if there were one group that has been affected the most, it would be young people. All across sub-Saharan Africa, there are swathes of young children growing up without parents who have already died from the disease.

According to a report released late last year by Unicef, 11m children under the age of 15 in Africa have lost one or both parents to Aids. By the end of the decade, that number is likely to have risen to 20m. In a dozen countries in the region, that will mean between 15 and 25 per cent of children will be orphans.

"They are a crisis that is massive, that is growing, that is long term and unless governments and the international community intervene, we are creating an explosive situation," says Carol Bellamy, executive director of Unicef.

The countries with the highest number are Botswana, Lesotho, Swaziland and Zimbabwe. Of those orphans, 50 per cent are between 10 and 14 years old, while 35 per cent are aged between five and nine.

Nor is the orphan disaster the only issue. Young people are also the most likely to become infected. According to one study, half of new infections were in the 15-24 age group. Young women appear to be particularly at risk, in part because of the pressure they face in some regions to have sex with older men, as well as their peers. Such catastrophic figures have prompted speculation about what happens to a society where one-quarter of the children are orphaned. Will crime explode and drug use soar? Will traditional social networks collapse?

A report from the World Bank also warned last year of the potential economic impact. Focusing on South Africa, it argued that the absence of parents in so many families would damage the process of passing knowledge to future generations and lead to lower attendance at school. The damage to the country's human capital, if unchecked, could lead to "economic collapse" within four generations.

A major part of the response to this crisis can only come from the state. As the World Bank report argued, the provision of anti- retroviral drugs to infected people is not only a humanitarian exercise; it will also keep parents alive for crucial parts of their children's development.

Improved education is another area where countries can help to reduce the social impact from Aids. Unicef argues strongly for the abolition of all fees on basic education to make it easier for children from orphan families to attend. It also argues that public policy should be directed at supporting extended families, which are most likely to pick up the burden from Aids deaths.

The death of a parent not only means grandparents and uncles and aunts often have to look after children, but it also places other financial pressures on extended families.

A study in four provinces in South Africa of households which had suffered an Aids death found that one-third of annual income was spent on funerals alone.

Many of the worst affected countries only had modest networks of social provision and healthcare even before being hit by HIV/Aids. Non- governmental organisations and churches can provide some of these services, but substantial contributions from international donors will be needed to support these initiatives.

Perhaps the greater role that civil society can play is in Aids prevention programmes. According to UNAids, a further 5m people became infected with HIV last year and there is concern among some health workers that the current focus on providing Aids treatment in poor countries will take resources away from the existing prevention efforts.

"People say that prevention programmes have failed, but in no African country - not even in Uganda - has there been a properly funded Aids prevention programme," says Debrework Zewdie, the director of the World Bank Global HIV/Aids programme.

A few lessons have been learnt from the experience in Uganda, however, where Aids prevalence has dropped dramatically during the last decade. For a start, young people were persuaded to begin having sex at a later age.

"In countries where there is a high prevalence of HIV, a young person's first sexual experience can be very risky and it takes a lot of discipline not to expose yourself to danger," says Peter Piot, executive director UNAids. "If you can persuade youngsters to delay their first sexual contact for a couple of years, you can have a big impact.

Community-based initiatives, where sexual advice comes from friends or respected local figures, are also seen as crucial by many health experts. It is this insight that a group of seven youth organisations, including the Scouts, Girl Guides and YMCA, have followed with an Aids prevention programme in five African countries.

"We are part of the local tapestry, part of the village," says Don Mohanlal, executive vice-president of the International Youth Foundation, one of the groups involved. "We are not some seminar being run by people from the big city."

While it might seem surprising for people in some western countries to see the Scouts and Girl Guides getting involved in sex education, Mr Mohanlal says they have the confidence and trust of local communities.

To learn more about the "Empowering Africa's Young People" initiative click here.