The World Health Organisation (WHO) is urging people around the world to be aware of the second wave of the influenza A/H1N1 pandemic as the northern autumn approaches, according to media reports Monday.

WHO Director General Margaret Chan warned that second and third waves had appeared in previous pandemics.

"We cannot say for certain whether the worst is over or the worst is yet to come. We need to be prepared for whatever surprises this capricious new virus delivers next " Chan said in a videotaped address to a symposium on flu in the Asia-Pacific region.

It is estimated that 250,000 to 500,0000 people die around the world every year from seasonal flu. However, some 1,799 people have died since the new virus was uncovered in Mexico six months ago, according to the UN health agency.

The symptoms of the new flu have turned out to be mild in most of the known cases, but it is proved to be more infectious than seasonal flu and more durable through the previous warmer months.

Influenza traditionally thrives during the northern autumn and winter. As the northern hemisphere edges towards the cooler season, emergency flu plans have been set into motion in many countries. While that includes many of the wealthiest nations -- with the most medicines, access to key antiviral drugs and vaccine development, as well as the best health care -- WHO spokesman Gregory Hartl pointed out that the hemisphere also includes five-sixths of the world's population. The vaccine is not expected to be ready for use until October and will only be available gradually.

Hartl said it was impossible to rule out the resurgence of the new virus before October to November, the more usual period for the growth in seasonal influenza.

"Everyone must be ready," said the WHO spokesman, "It is already amongst us, as we saw this summer."

(Agencies via Xinhua August 24, 2009)