A detailed analysis of influenza patterns indicates that the sharp dip in air travel after September 11, 2001 slowed flu spread and delayed the onset of the 2001-2002 U.S. flu season, report researchers at Children's Hospital Boston. Their findings, published in the September 12, 2006 issue of the online journal PLoS Medicine, suggest that limiting airline volume could buy critical time during a flu pandemic.
Most previous investigations of the effect of air travel on influenza spread have relied on simulations of flu activity rather than actual data.
"The post-September 11th flight ban was a natural experiment on the effect of flight restrictions on disease spread," says John Brownstein, PhD, the paper's lead author and a faculty member of the Children's Hospital Informatics Program (CHIP) at the Harvard-MIT Health Sciences and Technology program. "For the first time we've been able to show, using real data, that air travel spreads the flu, suggesting that reducing the number of air passengers might ameliorate a flu pandemic."
The spread of avian flu (H5N1) in Asia and Europe, including some likely cases of person-to-person transmission, has intensified debate over whether flight restrictions should be imposed to curb emerging flu pandemics. Both the World Health Organization (WHO) and the United States government are considering such restrictions.
Using data on influenza mortality from the Centers for Disease Control and Prevention (CDC), Brownstein and senior investigator, Kenneth Mandl, MD, MPH, a CHIP faculty member and an attending physician in Children's Department of Emergency Medicine, measured the rate of influenza spread across the U.S. during nine flu seasons, from 1996-97 to 2004-05.
During the first five flu seasons, flu mortality consistently peaked on or around February 17. But in the flu season after September 11, 2001, the peak was delayed until March 2, nearly two weeks later than average.
Contact: Rachel Pugh
Children's Hospital Boston