The World Health Organization (WHO) is urging the planet to brace itself for a second wave of the swine flu pandemic as the heavily populated northern hemisphere edges toward the cooler season when flu thrives.
　　"The WHO is still mobilized and wor来源：www.examda.comried," spokesman Gregory Hartl says as the global health watchdog kept an anxious eye on some "mysterious" patterns of illness associated with the new H1N1 virus that appeared in April.
　　Influenza traditionally surges to its peak during the northern autumn and winter.
　　WHO Director General Margaret Chan warns 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 says. "We need to be prepared for whatever surprises this capricious new virus delivers next," s来源：考试大he adds.
　　Some 1,800 people have died since the H1N1 was uncovered in Mexico and the United States 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.
　　With autumn approaching, northern countries have set emergency flu plans into motion, in some instances before the WHO’s long heralded formal declaration of a pandemic on June 11 that mwww.Ｅxamda.CoM考试就到考试大arked global spread of the virus.
　　While that includes many of来源：www.examda.com the wealthiest nations - with the most medicines, access to key anti-viral drugs and vaccine development, as well as the best healthcare - Hartl points out that the hemisphere also includes five-sixths of the world’s population.
　　More than 1 billion doses of preventive vaccine have been ordered by these countries.
　　But the vaccine is not expected to be ready for use until October and will only be available gradually, for the most vulnerable groups and health workers first.
　　The WHO has cut its estimate of maximum annual production capacity of 4.9 billion vaccines, currently focusing on about half or even one quarter of that amount. It is still unclear whether one or two doses will be necessary.
　　In the meantime, plans to mobilize stockpiles of anti-viral drugs, such as Tamiflu, reinforce healthcare capacity and close down schools temporarily to limit the spread of infection have already been tested in the first wave.
　　"Everyone must be ready," says the WHO spokesman. "It is already amongst us, as we saw this summer."