Vaccination 'would not have worked'

Vaccines may not have prevented the spread

Professor Joe Brownlie, head of pathology & infectious diseases at the Royal Veterinary College, examines whether vaccination could have been used to contain the spread of foot-and-mouth disease.

---

In any foot-and-mouth outbreak there is always the possibility, if not pressure, for ring vaccination around infected zones to prevent further transmission.

Put simply, ring vaccination is the vaccination of animals not identified as having contracted the disease, but who are within a designated area where outbreaks have occurred.

The use of ring vaccination in the Netherlands outbreak has once again begged the question: Should we embark on such a policy in the UK?

Before looking in detail at the UK, we should note the following about the Dutch situation.

Ring vaccination can only be effective in containing the outbreak if there is no animal movement beyond the area

Professor Joe Brownlie

The outbreak there is strictly limited and therefore much easier to isolate by ring vaccination.

The Dutch do not have highland farms with wandering livestock.

There is less movement of livestock from farm to farm in the Netherlands.

Back to the UK: ring vaccination was one of the recommendations made in the Northumberland Report into the 1967 outbreak in the UK, and it makes interesting reading now.

Temporary immunity

"[Slaughter] policy by itself should be adopted only if the conditions of meat import policy are such as to reduce substantially the risks of primary outbreaks occurring.

"If not, we would recommend the slaughter policy should be reinforced by a ring vaccination scheme."

Such schemes have been used before in outbreaks - though never in the UK - and have been considered a successful adjunct to control in local areas.

It would be difficult to see where ring vaccination could have helped in the initial phase of this outbreak

Professor Joe Brownlie

This is how ring vaccination works: Obviously, it takes two to three weeks after the first vaccination to initiate protective immunity.

With the use of high potency vaccine, immunity to aerosol challenge can occur within four days.

This immunity is temporary and needs a booster inoculation at three-four weeks to provide a longer term protection.

Thus for ring vaccination, a single inoculation may be sufficient for a short duration.

Sheep movements

However, with the present strain of the disease in the UK, (FMDV O-PanAsia) there appears to be limited spread through the air from sheep.

It should be remembered that it is not possible to fully protect pigs by vaccination.

There may still be a case for strategic vaccination of endangered animals

Professor Joe Brownlie

It is clear that ring vaccination can only be effective in containing the outbreak if there is no animal movement beyond the area of ring vaccination.

With the identification of outbreaks in the first seven days in Essex, Northumberland, Devon, Wiltshire and Anglesey, ring vaccination could not have controlled this national spread of virus.

It is already clear from Maff reporting that widespread sheep movements and marketing have been central to the epidemiology.

That being said, the subsequent two weeks have shown an even greater increase in disease locations across the UK, with particular enlargement of the Cumbrian and Devon outbreaks.

In retrospect, it would be difficult to see where ring vaccination could have helped in the initial phase of this outbreak.

Strategic vaccination

There may still be a case for strategic vaccination of endangered animals (such as the Chillingham herd and zoo animals), but the political consequences may be prohibitive.

The value of selective vaccination around or downwind of large pig units may also be suggested.

The use of vaccines extends the interval between the last FMD case and retrieving our foot-and-mouth disease-free status

Professor Joe Brownlie

The Northumberland Report considered general foot-and-mouth disease vaccination of all susceptible animals in the UK untenable, but proposed that in future there may be a role for ring vaccination.

In the first three weeks of this outbreak, it would appear that any ring vaccination would have had little influence on the extraordinary spread of the virus by the transport and marketing of sheep throughout the UK.

Even if ring vaccination were to be introduced now, it would almost certainly be necessary to return to a stamping out policy later, to regain foot-and-mouth disease-free country status.

The use of vaccines extends the interval between the last FMD case and retrieving our foot-and-mouth disease-free status from three to 12 months and possibly as long as two years.

Thus, it appears once again that the essential elements to control the foot-and-mouth disease outbreak are the availability of professionals in the field, the rapidity of diagnosis, informed policy - and courage at the top.