Strategy for Emergency Vaccination against Foot and Mouth Disease
The rationale for using emergency vaccination for foot and mouth disease is:
1. Fear that after the introduction of FMDV into a free region, it may spread out of
control; In particular, outbreaks in areas containing high densities of susceptible animals and inadequate resources of manpower or rendering plants for the slaughter and disposal of animals or outbreaks involving a predicted risk of airborne virus spread beyond the protection zone;
2. Availability of high potency vaccines.
It has been demonstrated (Salt et al., 1994 and 1996) that a high level of immunity can be induced by potent vaccines within a few days in both cattle and pigs. These experimental data were confirmed on several occasions under field conditions.
3. Availability of new tests that will differentiate between infected and vaccinated animals
The availability of these tests allows the vaccine to be used in a similar fashion to a marker vaccine.
4. Responding to public opposition to the implementation of total stamping out and the demand for an alternative approach or the impossibility of carcass disposal because of concerns about water (carcass burial) or urban air pollution by smoke of carcass burning.
5. The successful implementation of emergency vaccination will limit the number of animals experiencing the symptoms and poor welfare associated with FMD infection.
The objectives of emergency vaccination are:
1. to create a zone of vaccination outside the protection zone to protect animals against airborne infection ('protective' emergency vaccination); 'protective' emergency vaccination is vaccination carried out on holdings in order to create an immune zone and protect the animals within the area being vaccinated against airborne infection from the infected area;
2. to reduce the quantity of virus spread within the suspected infected area (='dampening down' emergency vaccination) 'dampening down' emergency vaccination is vaccination which should be used
only in conjunction with a pre-emptive slaughter policy in a known foot and mouth disease infected area where it is considered that there is an urgent need to reduce the amount of virus circulating and the risk of spread beyond the area. This may be indicated as a measure to assist pre-emptive slaughter particularly in
the following circumstances: a high density of animals (especially pigs); an overwhelming of the capacity to kill and dispose of carcasses within a short time period, poor infrastructure, inadequate manpower or delayed stamping out. In the event that this emergency vaccination is applied, stamping out procedures
should continue and be applied to the animals, irrespective of the implementation of vaccination.
3. to assist the completion of stamping out and disposal of carcasses and materials from infected premises by minimising virus transmission while this is taking place;
4. to reduce the severity of 'direct' economic losses. It should be noted, however, that during the 14 days following the vaccination of cattle and 7 days following the vaccination of pigs, virus transmission can occur from those species to susceptible animals in contact with them (Donaldson and Kitching 1989; Salt
et al. 1998). It is emphasised, however, that with effective surveillance, rapid reporting of suspected cases, rapid diagnosis and the implementation of control measures without delay, foot and mouth disease can be controlled and virus eradicated before outbreaks develop into epidemics. On the other hand, should the circumstances be appropriate for the implementation of emergency vaccination then the decision to do so must be made quickly.
Farmers whose herds/flocks are vaccinated and who suffer losses as a result of the restrictions placed on them should be fully compensated. If not, they are unlikely to co-operate with an emergency vaccination programme.
4 If a policy of emergency vaccination is implemented the trade restrictions imposed on the vaccinated area (region) and/or country will be in place for longer than if stamping out only, is used. Therefore emergency vaccination will result in an increase of 'indirect' costs. For countries with a large export trade in animals and animal products this economic consequence will be the strongest argument against the implementation of emergency vaccination
5. Criteria and factors affecting the decision to implement
The rapid and objective assessment of the determining parameters is crucial to the decision to commence a vaccination programme. If an analysis of parameters gives a result which supports a programme of protective emergency vaccination then the programme must be implemented without delay. It is emphasised that if decision-making and the required actions are delayed and as a consequence the initiative is lost and the disease becomes widespread, then the only remaining option may be a programme of either regional or national vaccination.
Several computer assisted models have been developed (De Jong and Diekmann 1992; Sanson 1995; Mackay 1997; Haydon and Woolhouse 1997; Donaldson et al. 1999), some of which are useful for strategic purposes e.g. operational planning, allocation of resources, whereas others are suitable for use in an epidemic e.g. to predict airborne spread of virus. These models are useful tools to assist in decision making and planning but for further development require the input of more data to refine their parameters and assumptions. It is essential that the necessary data (e.g. farm locations, stocking density) be collected and kept up to date in advance of an outbreak. It is recommended that simulation models be further developed and used by Veterinary Services and experts to test the effects of variations in the quantitative elements referred to in Table 1. A list of criteria for or against the decision to implement a 'protective'
emergency vaccination is presented in Table 1. When considering a decision to use emergency vaccination, these criteria should be assessed on a case by case basis.
8. Conclusion and recommendations
In conclusion, the Scientific Committee on Animal Health and Animal Welfare having reviewed the scientific and technological progress made in the field of FMD diagnosis and vaccine production considers that emergency vaccination can be a useful tool in the control of FMD outbreaks with a risk or tendency towards uncontrolled spread.
The National Contingency Plans should consider the possibility of emergency vaccination and provide an estimate of all logistical requirements such as the number of vaccination teams required in different areas, in order to complete the task as rapidly as possible.
This report of the Scientific Committee on Animal Health and Animal Welfare is
substantially based on the work of a working group of the Committee.
The working group was chaired by Prof. G. Panina.
The members of the group were as follows;
Prof. G. Panina, Dr. R. Ahl, Dr. M. Amadori, Dr. S. Barteling, Dr. K. De Clercq, Dr. A.I. Donaldson, Dr. P. Have, Dr. S. Marangon.
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