Abstract
BackgroundThe influence of air travel on influenza spread has been the subject of numerous investigations using simulation, but very little empirical evidence has been provided. Understanding the role of airline travel in large-scale influenza spread is especially important given the mounting threat of an influenza pandemic. Several recent simulation studies have concluded that air travel restrictions may not have a significant impact on the course of a pandemic. Here, we assess, with empirical data, the role of airline volume on the yearly inter-regional spread of influenza in the United States.Methods and FindingsWe measured rate of inter-regional spread and timing of influenza in the United States for nine seasons, from 1996 to 2005 using weekly influenza and pneumonia mortality from the Centers for Disease Control and Prevention. Seasonality was characterized by band-pass filtering. We found that domestic airline travel volume in November (mostly surrounding the Thanksgiving holiday) predicts the rate of influenza spread (r 2 = 0.60; p = 0.014). We also found that international airline travel influences the timing of influenza mortality (r 2 = 0.59; p = 0.016). The flight ban in the US after the terrorist attack on September 11, 2001, and the subsequent depression of the air travel market, provided a natural experiment for the evaluation of flight restrictions; the decrease in air travel was associated with a delayed and prolonged influenza season.ConclusionsWe provide the first empirical evidence for the role of airline travel in long-range dissemination of influenza. Our results suggest an important influence of international air travel on the timing of influenza introduction, as well as an influence of domestic air travel on the rate of inter-regional influenza spread in the US. Pandemic preparedness strategies should account for a possible benefit of airline travel restrictions on influenza spread.
Highlights
The influence of air travel on the geographic spread of influenza has been the subject of a number of simulation studies [1,2,3,4]
We provide the first empirical evidence for the role of airline travel in long-range dissemination of influenza
Our results suggest an important influence of international air travel on the timing of influenza introduction, as well as an influence of domestic air travel on the rate of inter-regional influenza spread in the US
Summary
The influence of air travel on the geographic spread of influenza has been the subject of a number of simulation studies [1,2,3,4]. We assess, with empirical data, the role of airline volume on the yearly interregional spread of influenza in the United States In both the northern and southern hemispheres, influenza epidemics occur annually during the winter ‘‘flu season.’’ the disease maps out a remarkably similar pattern in most years, little is known about the specific mechanisms by which geographic spread occurs. The researchers analyzed weekly government records on deaths from influenza and pneumonia in cities from nine regions of the US during the nine influenza seasons between 1996 and 2005 For each year, they determined the time it took for the epidemic to spread across the US and the date of the national peak in influenza deaths. They used government estimates of passenger air travel to explore any connection with the timing of the annual flu epidemics
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