Spatial Patterns in Transmissibility and Mortality Impact during the 1918-19 Influenza Pandemic

Gerardo Chowell - Los Alamos National Laboratory  

Abstract: The 1918-19 influenza pandemic ("Spanish flu") has been the most devastating of recent history with an estimate of at least 20 million deaths worldwide. Although the 1918-19 influenza pandemic had a devastating mortality impact, the effects of geographic and demographic factors on influenza transmissibility and death rates have not been explored at a refined spatial scale and could prove important to improve knowledge of influenza transmission mechanisms at the population level and may help design more efficient public health interventions in the case of a future pandemic. We used weekly influenza mortality during the fall and winter waves of the 1918-19 pandemic in England and Wales, at two spatial scales (333 administrative areas and 62 counties). We found significant variability of transmissibility across counties during the fall and winter waves. Transmissibility tended to be higher as a function of larger populations and higher population density.  The death rate in cities was relatively insensitive to population size whereas in rural areas influenza death rates decreased with population size. The1918-19 pandemic influenza dynamics were weakly affected by population size and density, in line with the invasion wave of a 'democratic disease'. Our results suggest that control measures should be spread out homogeneously across locations.

.