In doing so they would be inviting disease.

These methods may not allow the distinguishing of vaccinated from infected animals, so molecular biology approaches that detect specific DNA sequences are now preferred.

Killing an infected chicken is still a big economic loss for many poor farmers and they are therefore often reluctant to abandon their flocks.

But, she said, it has decided to broaden its response to prevent more people from becoming infected.

The severity of a pandemic has to do with when people get infected, how often are they going to develop really severe disease.