Matt Phillips digs up a 2006 PLoS Medicine article by John S. Brownstein, Cecily J. Wolfe, and Kenneth D. Mandl that found a correlation between the grounding of commercial aircraft in the days after 9/11 and the later peak of the 2001-2002 flu season, which peaked at the normal time in countries that did not ground their aircraft. The takeaway from this? “At the regional level, our results suggest an important influence of international air travel on influenza timing as well as an influence of domestic air travel on influenza spread in the US.”
[O]ur results suggest that inter-regional spread occurs by a different mechanism, where air travel may be an important mode of long-range dissemination of influenza. We find that the effect of airline volume on regional influenza spread is largely based on travel in November. Though influenza activity is highest between January and March, initial regional seeding of infection may occur earlier. Our results suggest that for a non-pandemic year, travel during the Thanksgiving holiday may be central to the yearly national spread of influenza in the US. Similarly, we found that international airline travel influences the absolute timing of seasonal influenza mortality.
The flight ban in the US after the terrorist attack of September 11, 2001, and the subsequent depression of the air travel market provided a natural experiment for the evaluation of the effect of flight restrictions on disease spread. The importance of airline activity was highlighted by the delayed peak of influenza in 2001–2002 following the period of reduced flying activity. This finding is further validated by the absence of a similar delay in influenza activity in France, where flight restrictions were not imposed.
Thus, even though air travel is a major agent in spreading flu, by the time infections peak, the virus has already been seeded around the country and the world.
Matt interviewed John Brownstein, and their discussion is available at the Middle Seat Terminal blog post.
For more: yesterday’s post.
