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Seasonal dynamics of recurrent epidemics

Nature volume 446, pages 533–536 (2007)Cite this article

Abstract

Seasonality is a driving force that has a major effect on the spatio-temporal dynamics of natural systems and their populations1,2,3,4,5. This is especially true for the transmission of common infectious diseases (such as influenza, measles, chickenpox and pertussis), and is of great relevance for host–parasite relationships in general1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23. Here we gain further insights into the nonlinear dynamics of recurrent diseases through the analysis of the classical seasonally forced SIR (susceptible, infectious or recovered) epidemic model6,7. Our analysis differs from other modelling studies in that the focus is more on post-epidemic dynamics than the outbreak itself. Despite the mathematical intractability of the forced SIR model, we identify a new threshold effect and give clear analytical conditions for predicting the occurrence of either a future epidemic outbreak, or a ‘skip’—a year in which an epidemic fails to initiate. The threshold is determined by the population’s susceptibility measured after the last outbreak and the rate at which new susceptible individuals are recruited into the population. Moreover, the time of occurrence (that is, the phase) of an outbreak proves to be a useful parameter that carries important epidemiological information. In forced systems, seasonal changes can prevent late-peaking diseases (that is, those having high phase) from spreading widely, thereby increasing population susceptibility, and controlling the triggering and intensity of future epidemics. These principles yield forecasting tools that should have relevance for the study of newly emerging and re-emerging diseases controlled by seasonal vectors.

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Figure 1: Epidemic time series together with their associated phase relationship and synchronization effects.
Figure 2: Effects of seasonality on population dynamics.
Figure 3: Testing the threshold prediction, equation (2).
Figure 4: The relationship between an outbreak’s current phase (month of year) and the maximum number of infectives I max in the following year’s outbreak.

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Acknowledgements

We are grateful for the support of the James S. McDonnell Foundation. A.H. was partly supported by the Porter School of Environmental Studies at Tel Aviv University.

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Author notes

  1. Lewi Stone, Ronen Olinky and Amit Huppert: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Zoology, Biomathematics Unit, Faculty of Life Science,

    Lewi Stone, Ronen Olinky & Amit Huppert

  2. The Porter School of Environmental Studies, Tel Aviv University, Ramat Aviv 69978, Israel,

    Lewi Stone & Amit Huppert

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  1. Lewi Stone
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  2. Ronen Olinky
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  3. Amit Huppert
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Correspondence to Lewi Stone.

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This file contains Supplementary Notes, Supplementary Figures 1-8 with Legends and additional references. (PDF 407 kb)

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Stone, L., Olinky, R. & Huppert, A. Seasonal dynamics of recurrent epidemics. Nature 446, 533–536 (2007). https://doi.org/10.1038/nature05638

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