The role of children in the spatial spread of 2009 Pandemic Influenza in the US

School-age children had a critical role in facilitating the geographic spread of 2009 pandemic influenza in the United States. This is one of the main findings that emerged from a paper published on PLoS Biology by a group of British and American scientists. The authors of the study used statistical and mathematical models to run an analysis on the weekly number of office visits with diagnosed influenza-like illness in 2009. Such data were obtained from a private sector electronic health database of insurance claims.

The approach used by the researchers allowed them to describe spatial and temporal patterns of the fall wave of the flu across 271 different locations within the US. Their model accounted for several factors that could have played a role in the diffusion of the infection: environmental elements like absolute humidity, population sizes, demographic factors, prior immunity due to the previous spring wave and so on.

From their findings, an explanation different from previous studies – that indicated environmental factors, population sizes and long-distance transmission as major determinants in the spread of the disease – came out. Indeed, the researchers found out that the 2009 pandemic fall wave was largely driven by short-distance transmission events, which in turn were mainly triggered by school openings. The low transmissibility of the flu also accounted for its slow spread.