A homegrown vaccine for humans against the H5N1 influenza virus, commonly known as bird flu, was on Wednesday approved by the State Food and Drug Administration (SFDA).

Worldwide, only the United States and the European Union have approved human vaccines against bird flu.

The SFDA approval follows two rounds of clinical tests involving 500 volunteers from 2005 to 2007.

The vaccine will enhance the country's capability to protect people from an influenza pandemic, said SFDA spokeswoman Yan Jiangying.

"Almost all known human bird-flu cases are caused by the H5N1 strain," said Yin Hongzhang, head of the biological product department of the SFDA.

But given the constant mutation of the bird-flu virus, it might be another strain instead that could trigger a pandemic, he added.

Yin Weidong, CEO of Beijing-based Sinovac Biotech and the vaccine maker, said in case of a pandemic, the WHO would offer the identified viral strain in three weeks for the producer to incorporate into the vaccine.

The production time for a vaccine against a new strain would take about four months, he said, adding that it takes two months for the H5N1 virus.

The vaccine-induced immunity lasts a year, similar to that of a seasonal flu shot, he added.

The company can churn out at least 20 million doses of the trivalent vaccines, Xinhua News Agency reported earlier.

Yan noted that the company will not sell the vaccine commercially.

"It will be purchased by the government for inclusion in the national strategic stockpile."

She said the SFDA streamlined approval procedures for the vaccine.

"It's also part of the task to secure an outbreak-free Beijing Olympics," she added.

Some 373 people worldwide have been infected with the virus since 2003, of whom 236 have died, according to the WHO. China has recorded 30 infections and 20 deaths.

To date, H5N1 influenza has remained primarily an animal disease, but experts fear the virus could acquire the ability for sustained transmission among humans.

(China Daily April 3, 2008)