GENEVA (AFP) - The World Health Organisation is urging the planet to brace for a second wave of the swine flu pandemic as the heavily populated northern hemisphere edges towards the cooler season when flu thrives. The WHO is still mobilised and worried, spokesman Gregory Hartl said as the global health watchdog kept an anxious eye on some 'mysterious patterns of illness associated with the new A (H1N1) virus that appeared in April. Influenza traditionally surges to its peak during the northern autumn and winter. WHO Director General Margaret Chan warned on Friday that there had been second and third waves in previous pandemics. We cannot say for certain whether the worst is over or the worst is yet to come, Chan said in a videotaped address to a symposium on flu in the Asia-Pacific region. We need to be prepared for whatever surprises this capricious new virus delivers next, she added. Some 1,799 people have died since the A(H1N1) was uncovered in Mexico and the US nearly six months ago, according to the UN health agency. By comparison, an estimated 250,000 to 500,000 people die around the world every year from seasonal flu, and overall the symptoms of the new pandemic virus have proved to be mild in the great majority of known cases. However, it has spread swiftly into 177 countries, proving to be more infectious than seasonal flu and more durable through warmer months. Through a full season in the southern hemisphere, the pandemic strain gradually became dominant. WHO monitoring showed that it was now on the decline there, except in South Africa, and in some later affected areas of Argentina, Australia and Chile. Some 182,000 people worldwide are known to have caught swine flu based on laboratory confirmed cases, but the WHO has long advised countries to give up counting; the true number may in the millions, according to some experts.