Apart from tourism, a human-to- human pandemic would also have a huge impact on airlines, restaurants and hotels as people stop travelling and stay at home, said Martin Meltzer, senior health economist at the US Centers for Disease Control and Prevention.

Economies would also see a rapid drop in demand for consumer goods - everything from refrigerators to automobiles, he said.

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"The SARS outbreak really informed us of what the impact might be," said Meltzer. "SARS was confined to four or five countries, while an influenza pandemic could occur around the globe."

Severe Acute Respiratory Syndrome in 2003 killed about 800 people, crippling air travel and tourism, particularly in Asia, causing massive losses in various sectors. Tourist arrivals fell by 20-70 percent and retail sales dropped by 5-10 percent in the second quarter of 2003, the International Monetary Fund said. It estimated that regional economic growth was cut by 0.6 percentage point.

But most industries recovered fairly swiftly once SARS was brought under control. The World Bank estimates a year-long bird flu pandemic would cost the world economy US$800 billion (HK$6.24 trillion). Some expect a pandemic could last six to eight weeks at a time, with renewed waves of infection.

The Asian Development Bank has forecast that a year-long shock would cost Asia as much as US$283 billion and would reduce the region's gross domestic product by 6.5 percentage points, hitting Hong Kong and Singapore the hardest.

The IMF believes the worst disruption for economies would come from high absenteeism in the workplace. Meltzer said that an influenza pandemic would likely last less than four months - depending on the size of countries affected - and probably hit growth for just one to two quarters.

"After that, I expect to see a great rebound," he said. "People will return and we will see normal growth rates."

The leisure and hospitality sectors might take longer to recover, while health care will need more time to recoup from the strains caused by a pandemic, he said.

Since re-emerging in Asia in late 2003, bird flu has killed at least 113 people, who contracted the H5N1 virus from contact with infected birds. There have been no cases of bird flu spreading between humans.

A US White House bird flu plan sets out detailed plans for closing schools in case of a pandemic and asks businesses to let employees stay home without sanction. It forecasts that 40 percent of the work force will be absent at the peak of a pandemic.

The plan assumes the worst - that if an influenza pandemic begins it will be months, if not years, before the best defence, a vaccine, can be formulated and manufactured. REUTERS