Research Article: Effects of reactive social distancing on the 1918 influenza pandemic

Date Published: July 12, 2017

Publisher: Public Library of Science

Author(s): Duo Yu, Qianying Lin, Alice PY Chiu, Daihai He, Gerardo Chowell.


The 1918 influenza pandemic was characterized by multiple epidemic waves. We investigated reactive social distancing, a form of behavioral response where individuals avoid potentially infectious contacts in response to available information on an ongoing epidemic or pandemic. We modelled its effects on the three influenza waves in the United Kingdom. In previous studies, human behavioral response was modelled by a Power function of the proportion of recent influenza mortality in a population, and by a Hill function, which is a function of the number of recent influenza mortality. Using a simple epidemic model with a Power function and one common set of parameters, we provided a good model fit for the observed multiple epidemic waves in London boroughs, Birmingham and Liverpool. We further applied the model parameters from these three cities to all 334 administrative units in England and Wales and including the population sizes of individual administrative units. We computed the Pearson’s correlation between the observed and simulated for each administrative unit. We found a median correlation of 0.636, indicating that our model predictions are performing reasonably well. Our modelling approach is an improvement from previous studies where separate models are fitted to each city. With the reduced number of model parameters used, we achieved computational efficiency gain without over-fitting the model. We also showed the importance of reactive behavioral distancing as a potential non-pharmaceutical intervention during an influenza pandemic. Our work has both scientific and public health significance.

Partial Text

The influenza pandemic of 1918 had been regarded as the deadliest pandemic in history. It had caused an estimated 50 to 100 million deaths worldwide [1, 2]. Due to its exceptional lethality and unusual epidemiological features, an in-depth understanding of the 1918 pandemic could provide insights to future influenza pandemic control and intervention. The 1918 pandemic was characterized by multiple waves of mortality. In the United Kingdom, the pandemic took place as three distinct waves: the first wave in the summer 1918, the second wave in the autumn of the same year, and the third wave in the spring of 1919.

Our study compared three forms of behavioral functions that described reactive social distancing, which assumes individuals either respond to the number of recent mortality or the proportion of mortality in the overall population. Using simple epidemic models to fit mortality cases in London boroughs, Birmingham and Liverpool, we showed the behavioral functions in the form of the Power function or the modified-Hill function outperformed the Hill function in terms of model fit. These results suggest that the proportion of mortality plays a more important role than the number of recent mortality.