H1N1 immunisation: too much too soon?

Abstract

In April 2009, a new influenza strain − H1N1 'swine flu' − was identified in Mexico with an apparent high case fatality rate (about 5%). As H1N1 spread rapidly throughout the world it caused not only a 'pandemic' but also widespread fear. However, overall, swine flu has been associated with fewer deaths (case fatality rate < 0.01%) than seasonal influenza (case fatality rate < 0.1% approx.),1and is of low virulence. While younger people were disproportionately infected by swine flu, it was people aged 50-60 years who had more frequent serious illness in terms of admissions to intensive care units and deaths.