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.
Evan Sparks's Aviation Policy Blog 
Swine flu: the dark side of international air travel
Posted in Evan's Commentary, tagged asia, australia pacific, health, regulation, usa on April 27, 2009| 3 Comments »
The outbreak and rapid spread of the H1N1 swine influenza virus in Mexico and now the United States puts policymakers and business leaders in a difficult position vis-a-vis air travel. Pandemics exploit all the virtues of the air travel boom of the past few decades — a system that transports people and goods for travel, commerce, and economic opportunity suddenly becomes a primary agent of deadly disease. It’s the downside risk of international economic and cultural integration. Such integration still pays handsome benefits, however, and the risks can be mitigated by a multilateral public health infrastructure poised to go into action.
We are now in a critical moment for U.S. and World Health Organization (WHO) policymakers and the international aviation industry. To declare a pandemic right now and impose travel restrictions (as the U.S. and WHO have not done) might overstate the threat from swine flu and excessively impair travel to Mexico and U.S. border regions. But this outbreak appears to be unusually aggressive, with high mortality, suggesting that policymakers should nip it in the bud regardless of the cost to the travel industry. As the first case was reported in Europe, EU authorities issued travel advisories for the United States and Mexico. The danger to the aviation industry from either an over-aggressive response or from a widespread pandemic is high. In April and May 2003, at the height of the SARS epidemic in Southeast Asia and Canada, air traffic in the Asia-Pacific region dropped 45 and 51 percent, respectively. U.S. carriers with extensive routes in Asia — Northwest and United, especially — also suffered. This is an even worse problem in a recession, in which the prospect of future growth after an epidemic-related contraction is limited.
Part of the problem for policymakers is that U.S. citizens are inexperienced with pandemic response procedures. We are used to frequent and easy travel, not only by air but also locally, for work, school, or recreation. With deadly infectious diseases like smallpox and polio eradicated, we have become lazy. Less than half the number of people for whom the annual flu vaccine is recommended get it. Activists play on fear to spread the unproven belief that ingredients of children’s vaccines can cause autism, and their success in misinforming the public is correlated with a spike in pediatric measles infections (Megan McArdle referred to parents who decline to vaccinate their children as “twee BoBo sociopaths“). Our cities are unaccustomed to quarantines. How would you react to an order to stay indoors except for essential business? Would you obey it? The discipline of disease control is honed over time and cannot be immediately adopted with success. Moreover, the scale of the United States is also unsuitable for a concerted public health response. It’s one thing to isolate SARS in a tiny enclave like Hong Kong (which is extremely vigilant, at any rate) or on an island like Taiwan (unconscionably prohibited by Beijing from receiving WHO support during epidemics, by the way).
Whether or not this swine flu outbreak becomes an epidemic or a pandemic, policymakers and airline industry leaders need to be prepared for the dark side of global integration. Preventing the spread of epidemic diseases should be at the top of any government’s list.
Further reading:
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