Flu's getting scarier by the day. Three-quarters of people infected with seasonal flu and swine flu in recent years have shown no symptoms. In other words, in today's world you might be down with influenza till the end, but show no symptom of it. In any case, for instance, not everyone with flu will have fever. Researchers analysed data gathered in England during the winter flu seasons between 2006 and 2011, including the 2009 H1N1 "swine flu" pandemic, and found that one in five of the...