To contain the spread of foot and mouth. Those in favour of vaccination say that the present policy of mass slaughter isn't working - there are simply too many animals to be killed. Pigs are particularly unpredictable. That would be impossible, given that there are 60m cattle, sheep and pigs in Britain, not to speak of a million deer and countless other wild animals which can contract or carry the disease. Animals within the cordon sanitaire would be vaccinated, and slaughtered later, when the disease is under control.
Treatment needs to be repeated every six months, and given to each new generation of animals.
The adoption of vaccination as a policy is a tacit admission that foot and mouth has not been eradicated. Their main argument is that it is impossible to distinguish between vaccinated animals, and those with the disease. However, according to EU rules, a limited vaccination programme would not necessarily mean an export ban. There is a total ban on export of meat and live animals, so long as the disease persists. That is why most farmers favour drastic action to end the crisis as quickly as possible.