VOA慢速英语 美国缓解学校对H1N1流感政策

　　The World Health Organization, the United Nations health agency, uses a system of six phases to warn of possible influenza pandemics. The current system has been used since two thousand five. For the first time the W.H.O. raised its alert level from phase four to phase five on April twenty-ninth.

　　Phase four means that a virus has gained the ability to cause community-level outbreaks. Phase five is marked by human-to-human spread of the virus into at least two countries in the same area of the world. This declaration is meant to warn that the time to plan for a pandemic is short.

　　Phase six would mean a global pandemic. Still, this would only mean that there are community-level outbreaks in at least one other country in a different area of the world.

　　The threat of H1N1 may have eased in recent days. But public health officials point out that flu viruses can return more aggressively after a few months. That happened with the so-called Spanish flu of nineteen eighteen which killed millions worldwide.

060s.com