NewScientist reports that many millions more people than previously thought might have been given a polio vaccine contaminated with a monkey virus that has been linked to cancer, reveal US researchers. Around 30 million people were exposed to the virus, SV40, through the vaccine between 1955 and 1963, after which the problem was thought to have been eliminated. But a new study suggests the Soviet polio vaccine, exported to China, Japan and Africa could have been contaminated until the early 1980s