The world's first vaccine against the leading cause of childhood diarrhoea, a virus that hospitalises thousands of children each year and kills one million in other countries, has won approval by the US Food and Drug Administration.Widespread vaccination with Rotashield could prevent on million American pre-schoolers every from getting diarrhoea caused by intestinal infection Rotavirus and keep 34,000 of them out of the hospital, said manufacturer Wyeth-Ayerst Laboratories, which is selling the vaccine created by the National Institutes of Health.