A ’Local-Global’ model for Seasonal Diseases: Influenza Subtypes Analysis Case Study

Abstract

Influenza epidemics in temperate regions display dynamics that are characterized by pronounced seasonal peaks during the winter. The general lack of influenza cases during the off-season may result from the virus physically disappearing at the end of the season, in which case it must be imported annually. Alternatively, it may result from persistent asymptomatic carriers or unnoticed local transmission chains that develop into local epidemics as conditions become conducive. Here I attempt to understand these differing explanations by analyzing the global distribution of the four major subtypes that comprise influenza over a period of 18 years based on FluNet data, the surveillance network and database compiled by the WHO, and the NCBI influenza data resource, a repository of relevant genetic information. Examining the annual proportion of each subtype, I find considerable variations in subtype annual proportions between the regions. Moreover, I find that seasonal influenza subtypes can remain confined to specific temperate regions, without showing measurable global presence. These results indicate that although largely undetected during the off-season, influenza is likely to persist locally, and imply a ‘local-global’ model where annual influenza epidemics are a mixture of local strains undergoing reactivation together with an influx of global variants.