Numerical forecasting of epidemics of influenza in Great Britain and Northern Ireland.

Examination of the weekly incidence data collected by the Research Unit of the Royal College of General Practitioners in England, Wales, Scotland and Northern Ireland, shows that, for influenza, the highest weekly total and the rate of decrease from such a peak over the next 4 weeks are highly correlated with the mean rate of weekly increase over the period 7 weeks before to 3 weeks before the peak week. Analysis of the mean rate of increase over 4-week periods of the incidence of the Febrile Common Cold showed that it rose to a critical value some 3-4 weeks ahead of the influenza peak week, thus identifying the significant initial period of influenza increase. Formulae for the numerical forecasting for the 7-week progress of an influenza epidemic were derived from the data for the years 1968-1974 (8 winters). These were then tested on the data for the years 1974-1981 (7 winters) with satisfactory results.