Travel restrictions useless against bird flu

By Maggie Fox

WASHINGTON (Reuters) - Restricting air travel is unlikely to stop a flu pandemic, and even the fastest action will merely delay it by a few months, British researchers said on Monday.

Their study highlights what most flu experts have been saying: until a vaccine can be developed, society is virtually helpless to stop a mutant form of avian influenza.

Ben Cooper and colleagues at the Center for Infections at Britain's Health Protection Agency used mathematical modeling to calculate the spread of an historic pandemic -- the relatively mild 1968-1969 influenza.

Then they modeled several different scenarios for the spread of H5N1 avian influenza into people. Experts stress that any new influenza virus has the potential to cause a pandemic, but H5N1 is now considered the most likely candidate.

"We show that under most scenarios restrictions on air travel are likely to be of surprisingly little value in delaying epidemics, unless almost all travel ceases very soon after epidemics are detected," they write in the online journal, Public Library of Science Medicine.

"Even if 99.9 percent of all travel could be stopped, epidemics in most cities would be delayed by no more than 4 months," Cooper's team added in the report, available on the Internet at http://dx.doi.org/10.1371/journal.pmed.0030212.

The H5N1 avian influenza virus has spread among wild birds and poultry at an ever-faster rate in recent months and is now found across Asia, Europe and much of Africa.

It is almost exclusively an infection of birds, but has sickened 205 people, killing 113 of them.

A few mutations could allow the virus to spread easily between humans, possibly sparking a pandemic that, depending on the resulting virus, could kill tens of millions.

WAITING FOR A VACCINE

International health experts and most countries are trying to gear up to fight a pandemic but a vaccine could not be formulated until the pandemic strain of virus actually emerges, and drugs that treat infection are scarce.

When severe acute respiratory syndrome (SARS) broke out in 2003, methods including quarantine and travel restrictions may have contained the virus, which nonetheless managed to infect 8,000 people globally and kill more than 700 of them.

But SARS is not as infectious as influenza and is only transmitted by people with symptoms. Flu can be transmitted before people look or feel ill.

"Elsewhere it has been shown that airport entry screening would be unlikely to detect more than 10 percent of passengers latently infected with influenza when boarding," Cooper's team wrote.

They used data from the International Air Transport Association for 2002 that gave the number of seats on flights between 105 cities.

"Even when 99.9 percent of air traffic was suspended, most cities had a low probability of ultimately escaping the pandemic, and delays large enough to be of clinical significance (6 months or more) were common only if interventions were made after the first few cases," they said.

Experts say they fear bird flu will mutate into a human-to-human transmitted form in a relatively undeveloped country with few screening tests -- where it could spread for some time before being detected.