This is why Singapore is now moving down to yellow alert at a time when the WHO might still move up to level six, which indicates a full-blown pandemic.

Explaining the decoupling of Singapore's five-colour alert levels from WHO's six-digit alerts, Health Minister Khaw Boon Wan yesterday said it is quite natural to 'lock-step' at the start.

Once the situation becomes clearer, countries will look at the national and regional situation and take their own steps, either to be more stringent or to be more relaxed.

He said that WHO's levels look only at how far a disease spreads, while Singapore's system also takes into account how virulent that disease is.

WHO's outlook is global, so it might call a level six should it see Influenza A (H1N1) spreading quickly around the world even though the illness remains a mild one.

For Singapore, however, there will not be a need for such a high level of vigilance for a fast-spreading but mild disease.

At his third influenza press conference, the minister said: 'We should shift to a sustainable level of precautions and control measures. We must avoid 'flu fatigue'.'

He said that once the dust has settled, he would suggest to WHO that its system of zero to six warning levels 'is probably too limited because it bogs you down. You're fearful of over-reacting, so you may end up under-reacting'.

Singapore was more careful in coming up with its colour scheme, perhaps due to its brush with Sars in 2003.

Read the full story in Thursday's edition of The Straits Times.