Beijing - China confirmed its first human cases of avian flu yesterday shortly after the government announced plans for possibly the biggest vaccination campaign in global history covering the country's entire poultry stock of 14 billion.

The measures, a sign of the authorities' growing desperation, came as China reported its 11th outbreak of bird flu in little more than a month and acknowledged that the virus had claimed its first confirmed human victim, a 24-year-old woman in Anhui province, a poultry worker.

Beijing also confirmed last night that a boy, aged nine, from Hunan province, who became sick last month but recovered, had the H5N1 virus. His 12-year-old sister fell ill and died though authorities cannot confirm she was a victim of bird flu because she was cremated before samples were taken. The government said earlier that the siblings were victims of pneumonia, though they became ill after eating sick chickens.

Adding to fears that the virus could mutate and lead to a global pandemic, Vietnamese scientists reported two new strains of the virus, which has killed at least 64 people, as well as ravaged poultry and forced a cull of tens of millions of birds across the region.

Since the outbreak in 2003 most of the reported casualties have been in south-east Asia. But in the past month China has become the new frontline in the battle to control the disease.

"It's not a surprise. It shows that China, like other countries that have bird flu in poultry, can have human cases," Roy Wadia, spokesman for the WHO, told reporters. He said there were at least two other suspected human cases, located in Hunan and Liaoning.

Until now Beijing's first response to the disease has been control ahead of openness. Quarantine has been established around areas of infection, and there have been mass culls. In Liaoning the authorities announced yesterday that they had finally halted the spread of the disease after slaughtering more than 10m birds.

On Monday, the central government said it would vaccinate all of the country's 14 billion chickens, geese and ducks - a huge logistical challenge given the remote locations of many farms and the small budgets of many rural authorities.

The H5N1 pathogen kills birds in less than an hour. Transmission to humans is still rare but about 50% of the people who have contracted the disease, mostly by handling poultry, have died. Health officials fear that as the pathogen spreads among birds the chances of it mutating into a form that can be passed between humans are increasing.

There were signs yesterday that the virus was changing. Vietnamese veterinarians at the Ho Chi Minh City regional animal health centre said they had identified new strains of H3 and H4 sub-types; though less virulent than H5N1 these could mix with the old to produce a disease able to spread more easily among people.

Such concerns have yet to be realised, but the issue is rising rapidly up the political agenda.

Yesterday, government ministers at the Asia-Pacific Economic Cooperation summit, in Busan, South Korea, called for greater regional cooperation to combat avian flu. Condoleezza Rice, the US secretary of state, told the annual forum: "We need to improve our ability to communicate accurate, relevant information quickly to the international community, and we must encourage our private sector to help us prepare for outbreaks before they happen."