In the wake of the swine flu outbreak, virologist Dr Mike Leahy goes back over 50 years of BBC archives to explore the history of pandemics: waves of infectious diseases caused by bacteria, viruses or parasites. Inspired primarily by the Horizon back catalogue, he works his way through the diseases that have been tackled head-on through the 20th Century: polio, malaria, smallpox, AIDS, and up to the present day with SARS and the H5N1 bird-flu virus. Each pandemic episode tells us something about the world and our place within it. In his trip through the ages and the archives, Dr Leahy charts science's ongoing battle with nature and questions which one is winning. He makes a reasonable fist of the exercise, but is somewhat up against it as his source material can be patchy - first triumphant about man's successes and then defeatist when the previous triumph didn't work out quite as planned, etc.