The flu could still hit Singapore, but there is no need for undue alarm. Scientists have confirmed that the two antiviral drugs, Tamiflu and Relenza, are still effective against it.

New information on the character of the virus, though still incomplete, means that Singapore need no longer operate under orange alert conditions, with temperature screenings at schools, workplaces and mass events.

More visitors will be allowed into hospitals, and not all doctors and nurses need to do work masked and gowned.

The measures will be rolled back progressively from Thursday. Come Monday, the alert level will go down to yellow, a shade above green - or the all-clear - in the five-colour system.

But Health Minister Khaw Boon Wan said on Wednesday: 'Let me stress that the situation remains dynamic and we must continue to stay vigilant and manage this crisis nimbly, scaling up or down as necessary.'

Since the outbreak was reported in Mexico late last month, Singapore has scaled up its preparations for a pandemic, setting aside beds and screening travellers, especially those from affected countries, which include Mexico, the United States and several European nations.

Singapore's flu pandemic alert colour code, which goes from green to yellow, orange, red and black, is based on knowledge of the virus - in particular, how infectious and deadly it is.

This differs from the World Health Organisation's pandemic alert levels, which progress from one to six and are based only on how far the virus has spread throughout the world, not its severity.

Last Thursday, after WHO raised its alert level to five, Singapore went into orange mode.