"If ever there was a demonstration of the power of science, it is the course of the fight billed 'Mankind v AIDS'. Until 1981 the disease (though already established in parts of Africa) was unknown to science. Within a decade it passed from being seen as primarily a threat to gay men, and then to promiscuous heterosexuals, to being a plague that might do to some parts of Africa what the Black Death did to medieval Europe. But now, though 1.6m people a year still die of it, that number is on a downward trajectory, and AIDS rarely makes the headlines any more. How was this achieved? The answer has two parts: sound science and international co-operation."