As the foot and mouth epidemic sweeps the UK and spills into other European countries, the question of whether to vaccinate or not has become crucial. Here, New Scientist unravels the complexities of the arguments.
Why is vaccination so controversial? The answer has everything to do with economics and very little to do with what's good for the animals. Using vaccination prevents farmers from selling animals and produce to countries free of foot and mouth disease, such as the US, Australia, New Zealand and Japan. Protecting these exports is also why animals with foot and mouth disease, which affects productivity but is not fatal, are always slaughtered.
But how can a vaccine jeopardise export trade? All it does is protect animals against the virus? It's not as simple as that, I'm afraid. Vaccines are not 100 per cent effective, so some animals remain vulnerable to the virus. Worse still, even vaccinated animals can still carry the live virus. If your country was free of disease, would you risk importing vaccinated animals?
What if vaccines were improved to be 100 per cent effective? Even then, there's a problem - it's impossible to tell vaccinated and infected animals apart. Current foot and mouth vaccines are made from killed virus. In blood tests, these dead viruses appear the same as live ones in an infected animal. The same is true of tests for antibodies that vaccinated animals make to fight the disease - infected animals have them too.
Isn't there any difference at all? Some researchers think there is. They say that a sufficiently sensitive test could spot fragments unique to the live virus (
Wouldn't the need to test all animals deter trade? Very possibly. Animals from a country with guaranteed disease-free livestock would require no testing, other than occasional spot surveillance. Imports from vaccinating countries would require much tighter surveillance, with frequent screening. Which would you choose to import?
Any other arguments against vaccination? Indeed there are. Today's vaccines don't protect the animals for very long. They wear off after about six months so vets would have to revaccinate periodically. Also, vaccines seldom protect against all seven major strains of the foot and mouth virus.
Does anyone vaccinate? Many countries whose farmers don't depend on exports to disease-free countries choose to vaccinate, e.g. China. Farmers who are too poor to either vaccinate or slaughter infected animals simply live with the disease, but have to accept much reduced productivity from the animals. But vaccination is often used in developing countries to "ring fence" outbreaks, preventing the virus from reaching neighbouring farms.
But vaccination is the kiss of death for countries that want to export to "disease-free" nations? Yes. It's taken as a sign that you haven't got the disease totally under control. Faced with these doubts, importers generally take the safe option and buy their goods from other disease-free sources.
So is it totally useless in countries which strive for disease-free status? No, not always. "Emergency" vaccination can be used locally to fight the spread of the virus - if it can be carried out faster than slaughter.
How does emergency vaccination work? The main idea is to buy time for overstretched slaughter teams. If livestock is condemned because of a nearby outbreak, vaccinating them means that they cannot catch and spread the disease while they await slaughter. This creates a "firewall" and stops the spread of the epidemic. Another approach is "dampening down". Here, infected animals are vaccinated and rapidly stop exhaling large amounts of the virus. Again this slows spread and again the animals are ultimately killed. Finally, it could in theory be used to protect rare or valuable breeds of livestock, which would not be later killed but would be quarantined.
What are the penalties if countries seeking "disease-free" status use vaccination? Countries using only slaughter are allowed to resume exports three months after the last reported case. The embargo automatically lasts nine months longer if countries have used emergency vaccination and slaughtered all the vaccinated animals. If countries allow any vaccinated animals to live on, they face at least two years of purdah after the last case. Britain's agriculture ministry says that this last scenario would cost the country up to £570 million per year in lost export markets. So again, it all comes down to economics.
So how do you decide whether to vaccinate or not? You have to weigh up the cost of the exports you lose if you do, against the compensation costs for the extra animals you are likely to have to kill if you don't. Professor David Harvey, of Newcastle University's Centre for Rural Economy, calculated recently that the UK could "afford" to slaughter every 10 years and it would still be cheaper than using vaccination. But not everyone agrees and the picture is also complicated by the general election that the government is widely believed to have planned for 3 May.
UK prepares to vaccinate (27/03/01)
UK epidemic may become eight times greater (23/03/01)
Dutch pledge to vaccinate vulnerable animals (22/03/01)
Virus spreads to the Netherlands (21/03/01)
Healthy animals join the cull (16/03/01)
Virus emigrates to Europe (14/03/01)
New vaccine could one day prevent slaughter (28/02/01)
Europe joins the slaughter (28/02/ 01)
Mass slaughter inevitable in UK (23/02/01)
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