EXETER — For decades, malaria vaccines have proved frustratingly difficult to develop. So scientists have been quick to welcome the recent news (December 2001) that a candidate vaccine tested in West Africa provided partial protection against the parasite Plasmodium falciparum, which causes the disease. The vaccine, given the less-than-catchy name of RTS,S/AS02, is the first of its kind to show convincing effects against the parasite. But the protection is incomplete and shortlived, at least in adults, and the vaccine's developers are already modifying it to try to improve its efficacy. Meanwhile, the existing form of the vaccine is already being tested in children, because the team have sufficient confidence in it to believe that it may benefit children more than adults.