The Cabinet Office and the Department of Health have released updated Planning Assumptions for the current A/H1N1 Influenza Pandemic, which indicate (but do not predict) worst case scenarios for pandemic planning.

The clinical attack rate for the population has remained unchanged at 30 percent and the absence rate for the workforce could peak at 12 percent.  Hospitalisation and fatality rates are both lower than previous planning assumptions (1 and 0.1 percent each).

The planning assumptions are based on analysis and modelling of data from both inside and outside the UK and reflect the latest evidence on the severity of the current A/H1N1 strain.  The assumptions contain a number of parameters, each taken at their 'reasonable worst case' value and should not be taken as a prediction of how the pandemic will develop.

The Planning Assumptions also take no account of the possible effect of vaccination against the pandemic strain until the government can be more certain about the timing of delivery and licensing of the vaccine on order.  The government also state that a vaccine will only have a large effect if a substantial proportion of the population can be vaccinated before the pandemic has peaked.