The vaccine is one that Hong Kong health authorities are checking in the countdown to a pandemic.

The WHO's regional director for the Western Pacific, Shin Young Soo, said the vaccine - the first registered by mainland authorities for the H1N1 strain - is just as effective as the Western-made vaccines already registered in the United States, Europe and Australia.

But its safety has still to be tested in mass-inoculation programs, though mainland authorities have started vaccinating people with it. "Pandemic flu is very mild, but the threat is very real and will grow," Shin said yesterday on the eve of a WHO regional meeting in Hong Kong that opens today.

He said experts have estimated that from 20 to 30 percent of the population in the WHO's Western Pacific region eventually will be affected - or between 448 million and 672 million people.

The worst-case death scenario is 0.1 to 0.5 percent of those infected, said Kasai Takeshi, the WHO regional adviser for communicable diseases, surveillance and response.

Shin, asked about vaccines that poor nations might turn to against human swine flu, was adamant: "The WHO will not compromise on safety and quality."

He said clinical trials in the West and the mainland have shown mild side effects for H1N1 vaccines that are commonly seen in vaccines against seasonal forms of flu.

"But we are talking about vaccinating millions and millions of people, so there is some possibility of serious side effects," Shin said. These include paralysis and neurological damage.

On the supply issue, Shin said it was fortunate that there needs to be only one injection of the H1N1 vaccine. "So we are in good shape."

Hong Kong Director of Health Lam Ping-yan, who along with other experts from the SAR has just visited the Beijing-based Sinovac plant for a first- hand look at its systems and product, said: "The vaccine produced at that particular plant is of very high quality and safe."

The group made the visit as Hong Kong continues to seek a vaccine supply for the local population.

Lam also said he understands that the mainland's vaccine production will be enough to inoculate 5 percent of its population. The mainland has reported about 10,000 confirmed cases but no deaths from the H1N1 virus.

Shin asked: "Why no death? According to their official report and our analysis, China may not be in a situation of what we call extensive local transmission, which Hong Kong is in now." Once it does happen, he said, "we can see a lot of severe cases."

Hong Kong has recorded 15 deaths from H1N1 following a 33-year-old woman dying on Saturday at Alice Ho Miu Ling Nethersole Hospital in Tai Po. The cause of death was confirmed last night.

Hong Kong continues to struggle against the virus as the wait for vaccine continues.

Eight people were in critical condition last night, including a 43-year- old man in Queen Elizabeth Hospital who was newly confirmed as an H1N1 victim. He was among 492 new cases confirmed in Hong Kong, taking the total to 22,054 yesterday.