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' Peak would signal infections falling but pandemic not over' WHO formal decision to be announced on WednesdayGENEVA (Reuters) - Flu experts convened on Tuesday to assess whether the H1N1 pandemic has peaked, the World Health Organisation (WHO) said.Such a recommendation - which is widely expected - would signal infections are falling in most countries but fresh waves can still occur and health authorities should remain vigilant.The WHO, a United Nations agency, declared last June that the new virus was causing the first influenza pandemic in more than 40 years and raised the alert level to the maximum 6 on its scale of 1 to 6."The main question will be to advise the WHO on whether we are still in phase 6 or whether we in effect have moved to what is called the post-peak period," WHO spokesman Gregory Hartl told a news briefing. "The pandemic will not be declared over."The WHO's emergency committee, composed of 15 experts and headed by Australian John MacKenzie, will make a confidential recommendation to WHO director-general Dr. Margaret Chan.She will inform the health ministries of WHO's 192 member states and the Vatican of her decision early on Tuesday evening, Hartl said. The WHO's decision will be announced formally by the WHO's top flu expert Keiji Fukuda on Wednesday.The H1N1 virus, which emerged in North America last March, spread with unprecedented speed and infected millions of people.It is confirmed as having killed 16,000 people, but it will take a year or two after the pandemic ends to establish the true death toll, the WHO says.SUBSTANTIAL OUTBREAKSThe pandemic sparked a race to develop new vaccines by drug makers including GlaxoSmithKline and Sanofi-Aventis, but has proved to be of moderate severity and many people failed to take up the new vaccine.Previous influenza pandemics have been marked by waves of disease activity spread over months, meaning the post-peak period could last for quite a while, according to the WHO.The final stage, called the post-pandemic period, is when disease activity returns to levels normally seen for seasonal influenza, it says."There is no on and off switch for a pandemic. It's not a single event. What we have to see is that the behaviour of the H1N1 virus becomes like the behaviour of other seasonal viruses," Hartl said. "At the moment, it is still causing substantial outbreaks of disease outside the normal influenza seasons and affecting groups who are not normally affected by seasonal influenza. So as long as that continues, it does not behave like seasonal influenza." Younger people, especially those with chronic medical conditions, and pregnant women continue to be at a higher risk of infection and viral pneumonia from the H1N1 virus, Fukuda told reporters last week.The WHO has warned that the H1N1 virus could still mutate or mix with the more deadly bird flu virus, which remains endemic in poultry in many Asian countries.