An influenza strain associated with pandemics in 1918 and 2009-10, as well as a Russian epidemic in 1977-8 and some lesser epidemics. It is associated with a relatively higher mortality in younger patients than the normal seasonal flu - presumed to be partly due to cytokine storm, partly background level of resistance in the elderly.
Risks:
The risk of H1N1 vaccination causing guillain barre syndrome (GBS) (flu vaccination per se approx 1:1 million) has been widely publicised, many reporters pointing out that the 1976 H1N1 vaccine programme resulted in an unexplained higher incidence of GBS (1:100K). However, even considering the higher figure, the risk of acquiring GBS following H1N1 flu itself is greater than the risk of acquiring GBS following the vaccine.
Effectiveness:
85 to 98 per cent of adults aged 18 to 64 will produce antibodies.
