The spatial anatomy of an epidemic: influenza in London and the county boroughs of England and Wales, 1918–1919

From uncertain origins in the spring of 1918, an apparently new variant of influenza A virus spread around the world as three distinct diffusion waves, infecting half a billion and probably killing around 40 million people. This paper examines the spatial structure of influenza transmission during the ten–month course of the epidemic in England and Wales, June 1918–April 1919, using the weekly counts of influenza deaths in London and the county boroughs as collated by the General Register Office, London. In addition, a particular case study of the borough of Cambridge is presented. From mid–1916, Cambridge contained, as well as its undergraduate population, a large naval contingent billeted in both the colleges and the town. It therefore affords the opportunity of studying the effect of the epidemic in contiguous groups with widely differing demographic characteristics. Through the application of a range of statistical methods (average lags, correlations and regressions), it is shown that the three waves that comprised the pandemic had fundamentally different spatial and temporal characteristics. The first, moving through a population that was a virgin soil to the new virus strain, was explosive in its north to south progress across the country. The second wave was somewhat slower in its rate of diffusion and displayed a south to north drift. Finally, the third wave reverted more closely to the form of the first. The spread of all three waves, however, was underpinned by a clearly defined process of spatial contagion. The Cambridge study showed the special characteristics of this pandemic in terms of the ages of those attacked: high rates were experienced across the age spectrum, a feature also seen internationally.