How vaccination might work

27 March 2001



How vaccination might work

By FWi staff

BRITAINS battle against foot-and-mouth disease intensified as the government requested permission from Brussels to vaccinate livestock.

A national policy of vaccination as the protection mechanism against foot-and-mouth is not a policy adopted nor favoured by the European Commission.

But agriculture minister Nick Brown believes that emergency vaccination could play a part in controlling outbreak of foot-and-mouth disease.

Such vaccination would either establish zones of protection between infected areas and the rest or the country, or reduce the number of cases in hot-spot areas.

Vaccinations have been used in Europe in the 1990s with a “stamping-out” or culling policy to tackle foot-and-mouth. But they have never been used in Britain.

If Mr Brown does now decide to vaccinate, stock around infected areas will be inoculated to create a “firebreak” in the hope that the disease stops spreading.

Immunity will take two to three weeks to take effect, although high-potency vaccines can provide immunity against airborne spread within four days.

Once it is clear that the disease has not spread beyond vaccinated stock, the vaccinated animals can be slaughtered and the carcasses destroyed or buried.

If the vaccinated animals are slaughtered, foot-and-mouth-free status can be regained after three months from the last confirmed outbreak.

But if the animals are not removed, international rules mean it could take between 12 months and two years for disease-free status to be resumed.

Alex Donaldson, head of epidemiology at the Institute of Animal Health, has said that vaccination should be used only as a last resort to free up resources.

Vaccinated animals that are protected against the disease can still replicate the virus and re-excrete it, infecting other animals, he believes.

Vaccinated cattle can become carriers of foot-and-mouth for up to three years, and sheep can pass on the infection to sheep, said Prof Donaldson.

So while vaccination can reduce the general level of virus of in the field, it does not prevent infection which can circulate subclinically.

There is even the possibility that if the vaccine is not fully inactivated, it can actually cause disease, said Prof Donaldson.

There are also concerns that trade partners will only accept imports if they are certain all vaccinated animals have been slaughtered.

It is usually impossible to distinguish infected animals from those which have been vaccinated, unless inoculated stock develop the disease.

However, if the government introduces ring vaccination and subsequent slaughter, such a problem would not be an issue.