The nation has developed an effective method for instant diagnosis of H1N1 influenza, known as "swine flu", Minister of Health Chen Zhu said on Thursday.

The new method, which features a testing chemical reagent, will be used at the center for disease control and prevention (CDC) offices at all levels, he told a news conference.

News of the breakthrough came as the World Health Organization raised the official alert level to phase 5, one notch below a full-fledged global pandemic.

"All countries should immediately activate their pandemic preparedness plans. Countries should remain on high alert for unusual outbreaks of influenza-like illness and severe pneumonia," WHO Director-General Margaret Chan said late on Wednesday.

In response to the heightened alert, Mexican President Felipe Calderon told his people to stay home from on Thursday for a five-day partial shutdown of the country, where 176 people have been killed by the epidemic.

As soon as China was warned by the WHO about the possible outbreak, research work began on an effective diagnostic method for quick detection, Chen said.

Only a few countries have the capacity for instant diagnosis of the virus, according to Dr Jeffrey McFarland of the US Center for Disease Control and Prevention China Office.

Chen also said China has asked the WHO, and some disease-hit countries including the United States, for the virus strain of the variant H1N1, which is crucial in the ongoing research for a vaccine.

Li Dexin, a senior official at China's CDC, said that the WHO might provide the virus strain by mid-May.

"Once we get the H1N1 virus strain, it's possible to produce the vaccine in three months," Li said.

Yang Weizhong, deputy director of China's CDC, said it is unlikely the country can avoid being affected because the window of opportunity to prevent a global outbreak had passed.

The best the government can do is to delay the spread of the virus to win more time for the research and production of vaccines, he said.

The health minister said that little is known about the new virus and it may mutate after human-to-human transmission.

But the government is "confident" and "capable" of preventing and containing the epidemic, he said, adding the country has gained valuable experience after fighting SARS in 2003 and the bird-flu virus in recent years.

"We have to do our best to prepare for the worst," he said.

Cases of H1N1 influenza will be immediately reported and infected people will be treated in isolation, he said.

There has no reported case in the country of H1N1 infection in either humans or animals.

(China Daily May 1, 2009)