Elderly may have some immunity to swine flu
US research suggests that older people may have some pre-existing immunity to the H1N1 human swine flu virus.
A study in the Morbidity and Mortality Weekly Report said that one third of people over 60 showed immune responses to H1N1, before being tested for immunity levels from previous influenza season vaccines.
The report said they had possibly come into contact with a virus similar to swine flu.