Restricting air travel as good as useless when it comes to stopping bird flu

May 3 2006

According to British researchers attempts to halt a flu pandemic by restricting air travel will have little effect and even in the best case scenario the speediest action will serve to delay it by only a few months.

The predictions by Ben Cooper and colleagues at the Center for Infections at Britain's Health Protection Agency add support to the views of the majority of flu experts that the only answer is a vaccine.

However developing an effective vaccine before the pandemic strain of a virus actually emerges is a tricky problem.

The H5N1 avian influenza virus currently spreading rapidly amongst the wild bird population and poultry can now be found across Asia, Europe and much of Africa.

It remains almost exclusively an infection of birds, but has made over 200 people ill and has killed 113 since 2003. It is contracted by handling sick poultry.

Experts fear this particular virus will mutate and acquire the ability to pass from human to human triggering a pandemic which could kill millions.

Cooper and his team used mathematical modeling to first calculate the spread of the 1968-1969 influenza pandemic which was comparitively mild.

They then modeled several different scenarios for the spread of a human H5N1 avian influenza which experts consider to be the most likely candidate for a pandemic.

They found that placing restrictions on air travel was unlikely to delay an epidemic unless virtually all travel stops immediately an epidemic is detected.

Even then that would only produce a delay of around four months.

When Severe Acute Respiratory Syndrome, or the SARS virus occured in 2003, quarantine and travel restrictions may have contained the virus, but 8,000 people worldwide were infected and more than 700 died.

But SARS was easier to deal with as it is not as infectious as influenza, and is only passed on by people with symptoms, whereas influenza can be transmitted before people look or feel ill.

Cooper says it has already been shown that airport entry screening would detect at the most 10 percent of passengers latently infected with influenza when boarding.

The computer-simulated scenario follows recent research by Imperial College, London which demonstrated that the United States could presently do little to stop a pandemic.

According to Cooper the computer model was based on "optimistic assumptions" and that shutting down nearly all air travel would not stop the flu's spread because vaccine supplies were limited.