Vaccines are useless against this virus

There is no vaccine available against bird flu. Existing vaccines are unlikely to be effective against the new strain.

Researchers are working to develop a vaccine targeted at the H5N1 strain but even if it is successful, to manufacture sufficient quantities to protect the world's population from a pandemic will take years. A generic H5N1 vaccine would not prevent infection but it might lessen its severity and save lives. Countries including the UK are relying on the anti-viral drug Tamiflu.

Anti-flu drugs work in a different way from vaccines and can be used against any strain of flu. But they have a limited effect, shortening the course of the illness by a day or two, provided they are taken within 48 hours of infection. In outbreaks of ordinary human flu, they can prevent secondary complications such as pneumonia and reduce infectivity, cutting the rate of spread.

It is hoped that they would be similarly effective against bird flu in humans, saving lives by reducing the severity of the illness. But it is not certain.

The Government has ordered 14.6 million courses of Tamiflu, enough for a quarter of the population, at a cost of £200m, from the manufacturers, the Swiss pharmaceutical company Roche. About 900,000 doses have been delivered.

There is a worldwide shortage of Tamiflu because the raw materials from which it is made are scarce and the manufacturing process is slow and complex. If a human pandemic were to arrive in the UK this winter, the shortage could provoke panic, with hospitals under siege.