Besides the low cost, the vaccine does not require refrigeration or special storage. Aids has caused an estimated 100m deaths this century. More than half have been in sub-Saharan Africa, although deaths in China have risen steeply in the past 10 years. Uganda was one of the first African countries to tackle the problem. The low price means that inoculation programmes are feasible in poorer nations.
Conventional vaccines use a dead or modified virus to trigger the immune system.
It is produced from genetically modified bacteria, which means it can withstand high temperatures and long periods in storage.