The vaccination programme has won support from international organizations, including the World Health Organization and the World Organization for Animal Health, he said.

Jia strongly refuted some media reports that vaccinated chickens may carry the bird-flu virus without showing any symptoms.

"So far there has been no confirmed case of a healthy, live chicken being a carrier of the virus," he said.

China's neighbours, such as Viet Nam, are using China-made vaccines, Jia said.

"We have been using Chinese vaccines nationwide and there has been no problem regarding quality," Hoang Van Nam, deputy director of the Animal Health Department in Viet Nam's Agriculture Ministry, was quoted by Reuters as saying over the weekend.

"We have just completed tests of 20,000 poultry nationwide and found no trace of bird flu," the official said.

Vaccines used on the Chinese mainland include one that can effectively guard waterfowl from H5N1, and the world's first live vaccine developed by Chinese scientists against both bird flu and Newcastle disease two killer infections for poultry, according to Jia.

"Our vaccines are the most effective in the world," Jia told China Daily.

By Friday, the ministry had apportioned 2.967 billion vaccines to local departments. Most of the areas will be well prepared by the time migratory birds fly north in mid-April, Jia said.

Meanwhile, China is closely monitoring mutations of bird flu and is ready to make new vaccines to cope with possible major mutations, he said.

Confident as he was in the efficacy of vaccines, Jia said he was worried that not all poultry raised in backyard farms would be vaccinated.

The ministry has dispatched 28 inspection teams throughout the mainland to see if bird-flu prevention and control measures are in place, specially in rural household poultry farms, he said.