Restricting air travel could slow down the spread of bird flu pandemic

According to researchers, a noticeable drop in the number of people travelling by air following the September 11 attacks, had an effect on the start and spread of the 2001-2002 U.S. flu season.

They say this confirms that air travel could help spread a bird flu pandemic and restricting air travel could delay the spread of a deadly virus and give more time to prepare vaccines, drugs and adopt other measures.

The researchers at the Children's Hospital Boston say this is the first time real data has been used to show that air travel spreads the flu.

Study leader John Brownstein says while there is no way to stop a pandemic completely, reducing the number of air passengers might lessen the impact.

It seems the team recognised the opportunity for a "natural experiment" when air traffic fell after the Sept. 11 attacks to 3.5 million passengers in September of 2001, from 4.9 million passengers in September 2000.

Dr. Kenneth Mandl, who worked on the study with Brownstein says they had been trying to map the spread of flu and they looked at data from the U.S. Department of Transportation and the Centers for Disease Control and Prevention for the years between 1996 and 2005.

In the Northern Hemisphere the flu season usually starts in September or October, and peaks between January and March and they noticed that the 2001-2002 flu season was highly unusual.

They soon realised that they were seeing the effect the 9/11 attacks were having on the influenza season.

In the first five flu seasons, flu deaths peaked on or around February 17, but in 2002 the peak was delayed by two weeks, until March 2.

During the 2001-2002 flu season, it took 53 days for flu to spread across the United States, 60 percent longer than the average time of 33 days.

In comparison in France, where flight restrictions were not imposed, there was no delay in flu activity during the 2001-2002 flu season.

Brownstein says the more domestic travel, the faster the spread of flu, and the more inbound international travel, the earlier the influenza season begins.

A range of viruses cause influenza and as a rule the mix changes slightly from year to year; significant changes in the virus means more people become ill, often seriously ill, and more die.

According to the World Health Organization, every year anywhere between 250,000 and 500,000 people die from influenza, and a pandemic which occurs about every thirty years, can kill millions.

Experts fear that the H5N1 avian flu virus now killing birds worldwide could mutate and acquire the ability to transfer from human to human, triggering the next pandemic.

The H5N1 virus currently doing the rounds has to date infected 244 people and killed 143, and remains a disease of birds which is contracted almost always by handling sick or diseased fowl.

Governments, large companies and organizations are making preparations for such a pandemic by stockpiling vaccines they hope will provide some protection.

The researchers, both from Harvard Medical School, suggest that limiting airline travel could buy critical time during a flu pandemic and it is reported that both the World Health Organization and the United States government are considering such restrictions.

Their findings are published in the September 12, 2006 issue of the online journal PLoS Medicine.