The seasonal campaign, the largest scale in the world, is expected to further fortify the country's defences against the fatal bird flu.

"The only way to prevent the spread of bird flu is to step up vaccinations," Vice-Minister Zhang Baowen told a press conference held by the State Council Information Office yesterday.

"We'll strictly check how vaccination work is being done in local areas."

In the first half of this year, vaccines were administered to at least 4.88 billion birds, and an estimated further 5 billion fowl will be vaccinated between now and the end of the year, Jia Youling, chief of the ministry's Veterinary Bureau, told China Daily yesterday.

Li Jinxiang, deputy chief of the bureau, said the ministry has made detailed plans for the vaccination, and will also monitor for signs of vaccine-resistant strains.

A national tele-meeting is scheduled for the middle of this month to formally unveil the vaccination campaign, according to ministry sources.

Li conceded that bird flu virus may proliferate through domestic poultry trade, as studies have found that some waterfowl may carry viruses but show no symptoms.

Other challenges for bird flu control include the difficulty of vaccinating all courtyard farm flocks in some remote mountainous areas. There are also the problems brought by migratory wild birds, some of which, according to the ministry's monitoring, carry viruses, Li told the press conference.

"Governments at all levels along with veterinary departments are striving to solve these difficulties," Li said.

Li also said China is active in promoting global and regional collaboration in bird flu control.

The country has provided technical support for its neighbours including Viet Nam, Mongolia, the Democratic People's Republic of Korea and Indonesia.

It has also co-operated well with the World Health Organization (WHO), the Food and Agricultural Organization of the United Nations and the World Bank, Li said.

China provided five samples of bird flu strains to the WHO in 2004, and is in the course of exchanging strains with international laboratories designated by the WHO.

"When viral strains cross international borders, special protocols are needed and we are working to complete those," he said.

China's most recent outbreak of H5N1 bird flu was identified in mid-August at a farm in Changsha, capital of Hunan Province in Central China.

In a related development, Indonesia has purchased 91 million doses of bird flu vaccine from China and already received 31 million doses, with the remainder expected to arrive early this month, the Antara news agency quoted Musni Suatmojo, director of veterinary with the Indonesia's Ministry of Agriculture, as saying on Monday.