A top World Health Organization official warned Friday that the avian flu virus is evolving quickly and urged heightened vigilance because the strain in China appears to have increased in virulence. «The virus remains unstable, unpredictable and very versatile,» Shigeru Omi, the WHO's Western Pacific regional director, said at a news conference, according to AP. «Anything could happen,» he said. «Judging from the way the virus has behaved it may have new and unpleasant surprises in store for us.» Omi said the H5N1 virus is behaving differently in China and Vietnam. China has reported no human cases of bird flu while Vietnam has had 38 of Asia's 54 human deaths. But the cases in Vietnam appear to be becoming less deadly, with fatality rates dropping from a high of 60 to 70 percent last year, to about 10 to 20 percent so far in 2005, Omi said. Vietnam has also seen more asymptomatic cases, where people are infected but don't develop symptoms. --More 1427 Local Time 1127 GMT
