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Aims of 'Ring' Vaccination
Vaccine Banks
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A policy of 'stamping out' is the preferred option for the control of FMD. The option of
emergency 'ring' vaccination is employed only if an FMD outbreak threatens to become
extensive, or particularly valuable breeding stock are at risk.
Emergency vaccination can have one of two objectives:
1 - 'Dampening down' emergency vaccination aimed at reducing the amount of virus produced
within an infected area in circumstances where it is not possible to slaughter and dispose
of animals quickly enough to prevent spread of disease
2 - 'Protective' emergency vaccination carried out to produce an 'immune belt' of
vaccinated, protected animals around an infected area and thus reduce the risk of
spread of infection out of the infected area, particularly by airborne transmission.
If high-density pig or cattle areas are affected, it would be very difficult to slaughter
sufficiently quickly to control disease spread. In addition, in any high-density livestock
area, logistical, welfare and environmental problems would prevent mass slaughter. The
compensation costs could also become prohibitive. It should be kept in mind, however, that
the indirect costs through more protracted trade embargoes will be higher after emergency
vaccination.
Effective deployment of 'ring' vaccination depends on each country having appropriate
contingency plans. These should include the capacity for a rapid mobilisation of adequate
staff, vehicles, identification equipment, vaccine and vaccination equipment, cold chains,
handling facilities and measures to minimise the risk of further spreading the disease.
Coordination of vaccination teams will be performed by the local Crisis Centre.
Once movement restrictions associated with the Protection and Surveillance Zones have been
established, the major threat of extension of an outbreak is from wind-borne virus,
especially if pig herds are involved. A short-range computer model can interpret
epidemiological, topographical and meteorological information to assist with control. In
this way an 'at risk' area, having received sufficient wind-borne FMDV to produce disease
in cattle, the most susceptible species for airborne infection, can be accurately predicted.
If a decision to 'ring' vaccinate is made vaccination areas can be defined which fall
outside the 'at risk' area. All susceptible species will be vaccinated and identified, the
main target being grazing cattle, which are seen to be at greatest risk from aerosol
virus. In the EU, it is envisaged that a single vaccination will be given to all animals
in the ring, but a booster vaccination may be given after 21 days.
Controls after 'ring' vaccination
In view of the risk that vaccinated and infected ruminants can be FMDV carriers, and the
attendant problem of being unable to identify accurately these carriers, all 'ring'
vaccinated ruminants would be marked and held within the vaccination zone. For a defined
period (the length of which is still under consideration, but possibly up to one year),
there would be no movement of live ruminants out of the zone and only de-boned, and
matured carcasses with lymphoid tissues removed, could be sold for human consumption.
After this period all non-vaccinated ruminants could leave the zone, and vaccinates would
have to be FMDV negative in a probang test before release.
There are severe disadvantages in resorting to 'ring' vaccination. These include
restrictions upon the vaccinated, susceptible species for up to at least two years,
requiring the identification of individual vaccinated animals, and the policing of
movement restrictions. In addition, there is the possibility of FMDV carrier movement
within the Community and the loss of exports to FMD-free countries if 'regionalisation'
is not accepted. Therefore, although 'ring' vaccination is a useful tool in 'emergency'
FMD control, it is not without long-term repercussions.
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