The World Health Organization says the A/H1N1 flu could still mutate into a more virulent form and spark an influenza pandemic. This has the potential to circle the globe up to three times.

The WHO says the impact of any pandemic would vary, because a virus that causes only mild illnesses in countries with strong health systems could become "devastating" in those with weak health systems, insufficient drug supplies and poorly equipped hospitals.

It says the A/H1N1 virus appears to be more contagious than seasonal influenza, and practically the whole world lacks immunity to it. The WHO made the warning on Tuesday.

The number of A/H1N1 flu deaths across the globe stands at 63, with 58 in Mexico, three in the US, and one each in Canada and Costa Rica.

Confirmed cases are estimated at more than 59 hundred in 33 countries and regions.