April, including 429 deaths

A study by Oxford Economics - a forecasting consultancy whose clients include multinational corporations and government - said recovery could be delayed by a couple of years due to the swine flu pandemic.

'Although so far the social and economic impacts have been very small, if infection rates were to rise much further, significant costs could be expected,' it said.

Comparing the outbreak to the 2003 SARS crisis, it said that outbreak had occurred at a time of strong economic growth. Both consumption and growth had returned as soon as the epidemic was considered under control.

'This time around, such a sharp rebound is unlikely,' it said.

'There is a risk that swine flu tips the United Kingdom and the world economy into deflation. This is because the pandemic would hit at a time when businesses and banks are still reeling from the economic crisis.'

On Thursday, England's chief medical officer Liam Donaldson said that in a worst case scenario, around one in three Britons could be infected and 65,000 could die.

The WHO policy shift was partly motivated by the 'mildness of symptoms in the overwhelming majority of patients, who usually recover, even without medical treatment, within a week of the onset of symptoms'.

In some countries, the investigation and laboratory testing of all cases had absorbed huge resources, leaving health systems with little capacity to monitor severe cases or exceptional events that might mark an increase in the virulence of swine flu.

In the last table released by the WHO on July 6, the health agency had recorded 94,512 laboratory-confirmed cases in 136 countries and territories since April, including 429 deaths.