TECHNIQUE

Emergency Mass Vaccination for Foot-and-Mouth Disease (Disease Investigation & Control - Treatment and Care)

Summary Information
Type of technique Health & Management / Disease Investigation & Control / Treatment & Care / Techniques:
Synonyms and Keywords  
Description Vaccination of susceptible animals over a wide geographical area, such as a country, in the face of an outbreak of foot-and-mouth-disease.
Appropriate Use (?)
  • In order to control the disease without slaughtering excessive numbers of livestock
  • To reduce the risk of the disease spreading into areas with large populations of wildlife in which the disease might then circulate.
    • If FMD became endemic in a wildlife population, control of the disease in that population might require the eradication of that wild population. this may be difficult/impossible, and may not be publicly acceptable.
    • If FMD became endemic in a wildlife population, control of the disease in domestic livestock would require ongoing (routine/prophylactic) vaccination of livestock and/or the setting up of barriers to prevent contact between domestic livestock and wild animals.
  • Both the EU Strategy for Emergency Vaccination and the Northumberland Report (The Report of the Committee of Inquiry on Foot-and-Mouth Diseases 1968) make it clear that if emergency vaccination programmes are not implemented rapidly, and FMD becomes widespread, regional or national vaccination (mass vaccination) may be the only remaining option for the control of the disease.
    • "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." (D35.w1)
    • "If, as would happen in the event of a large number of scattered outbreaks, large areas of the country and large numbers, say fifty per cent of animals were involved in ring vaccination, then general prophylactic vaccination would probably become inevitable." (D36.Para207).

Vaccinated animals are protected against FMD. They will not usually develop the disease. This means that:

  • They will not develop the clinical signs of FMD.
    • No loss of milk output
    • No weight/condition loss
    • No loss of growth rate
    • No deaths of young animals
    • No loss of draught power
    • No welfare problems associated with severe disease
    • No secondary infections of lesions
    • No prolonged convalescence of recovered animals.
  • They will not excrete large quantities of virus which could infect other animals; the total amount of virus in the environment will be reduced. (J70.12.w1)
    • However, low level excretion may occur with subclinical infection if infected prior to fully developing protection, but much less than with full disease.
    • However, may still develop carrier state if exposed to virus (ruminants, not pigs) with slight risk of passing virus to other animals.
    • N.B. Number of carrier animals decreases with time. (J19.73.w1).
  • Reduced numbers of farms on which FMD occurs (J3.102.w6).
  • Except where used as part of a "vaccinate and cull" policy around infected areas, livestock which have been vaccinated do not need to be culled.
  • Meat, milk and other animal products from vaccinated animals may enter the human food chain as usual. and other
    • There are no risks to human health health from FMD vaccines (which are inactivated vaccines) entering the food chain (W32.Apl01.sib1).
  • The loss of genetically valuable stock and rare breeds, including e.g. hill sheep which are particularly adapted to their local area, is avoided. (D35.w2)
  • The loss of income to farmers associated with loss of stock due to either infection on the premises or extended culling is avoided, along with the costs to the government of compensation.
  • The costs and environmental risks associated with disposal of carcasses following culling operations may be greatly reduced.
  • Movement restrictions may be lifted within a relatively short time following the end of the period in which exposure to infection may occur (e.g. two or three weeks) (J21.23.w1)
  • Could be useful to prevent virus entering populations such as gated or hefted upland/moorland sheep and susceptible wildlife populations (e.g. deer) in upland areas where domestic and wild species share habitat (D35.w2).
    • FMD in the wild deer population could be a source of infection for domestic livestock.
    • Vaccination of wild deer would be very difficult or impossible, however vaccinating livestock would reduce the risk of the disease being passed to deer and therefore the risk of the disease being passed back from deer to susceptible livestock.
Notes
  • "FMD-free" status may be regained 12 months after the last case of FMD even if the vaccinated animals are not slaughtered (D35.w2).
  • The option to use emergency vaccination was retained by the European Union when routine vaccination was abandoned after 1991, and stores of highly concentrated vaccine were set up to allow the rapid use of emergency vaccination if required.
  • Concentrated inactivated FMDV antigens may be stored at ultralow temperatures which allow stable storage for several years and formulation of vaccine when required (J70.16.w2).
Complications/ Limitations / Risk
  • Disease control considerations:
    • Increased risk of disease spread associated with increased contact between animals and personnel involved in vaccination.(J3.131.w1, J16.22.w1).
    • Some animals may be in the early incubation stages of FMD at the time when they are vaccinated, and a small proportion may become carriers (D36.Para124).

    Difficulties in differentiating between animals which have been vaccinated and those which have been infected.

    • Vaccinated animals will have antibodies to FMDV.
    • Tests usually used for detecting antibodies to FMDV cannot give information as to whether an animal has been vaccinated (but not infected) or infected (whether or not it has been vaccinated).(J42.118.w1).
    • Also, seropositive animals (not including pigs, as these do not become carriers) are excluded from international trade. (J42.118.w1).
      • If no vaccination is used, or ring vaccination followed by slaughter of vaccinated animals and serological surveys show an absence of FMD antibodies, "free from FMD" status can be regained after three months from the last outbreak. (J42.118.w1).
    • If vaccination is used, "because serology cannot detect carrier animals and because FMD can infect immune animals and cause sub-clinical disease in partly immune animals, it is acknowledged that FMD may circulate undetected in a vaccinated population" (J42.118.w1).
    • Therefore, if vaccination is used, "free from FMD" status cannot be regained until two years after the cessation of vaccination (if vaccinated animals are not slaughtered). (J42.118.w1).
    • However, recently-developed serological (blood) tests are able to distinguish between animals which have been vaccinated against FMD and those which have actually been infected with foot-and-mouth disease virus. (J69.20S2.w1, J70.17.w2, J71.142.w1, J71.143.w1, J71.145.w1).

    2) Possibility of vaccinated animals becoming carriers (following undetected mild/subclinical infection, or without ever developing a general infection) and then infecting unvaccinated animals.

    • Ruminants, with or without developing clinical disease, and including animals which have been vaccinated and then been in contact with live FMD virus, may carry live FMD virus in the pharynx, for up to three years (cattle), nine months (sheep), less than nine months (goats). (J42.118.w1).
      • Carrier animals may represent a risk of initiating further outbreaks of FMD (J42.118.w1).
      • Epidemiological evidence suggests that carriers do sometimes transmit virus to susceptible animals in close contact with them.
      • Experimentally, it has been possible to prove transmission of virus from carrier animals only very rarely.
      • The factors which determine whether or not virus in the throats of carrier animals infects other animals are not known.
    • Detecting carrier animals is not easy.
      • Testing for carrier status requires sampling cells and mucus from the pharynx (back of the throat) using a probang cup. Virus is only excreted some of the time and often at low levels. Sensitivity of testing is probably 50%, that is, about 50% of carriers, tested on one occasion, would NOT be detected.
      • However, this can be improved by repeated sampling (J42.118.w1).
      • PCR techniques may be used to detect carriers using probang specimens: these are potentially more sensitive than detection using tissue culture (J35.148.w1)
      • There is no blood test to detect carrier animals; there is the possibility that vaccinated animals may occasionally become carriers without developing antibodies to the virus.
      • However, used on a herd basis it should be possible to distinguish by blood tests between vaccinated herds in which the virus has circulated (and in which there might be carriers) and those which have never encountered the virus (in which there cannot be any carriers). (J69.20S2.w1).

    3) Need for definite identification of vaccinated animals.

    • Vaccinated animals would need to be marked, to avoid the mixing of potentially carrier animals with the seronegative population (J70.12.w1).

    4) Perceived public health risks from meat, milk etc. from vaccinated animals.

    • N.B. There are no risks to human health from FMD vaccines (which are inactivated vaccines) entering the food chain (W32.Apl01.sib1).
    • Meat from animals vaccinated against FMD is commonly eaten in many countries, including countries which are free from FMD. There are no labelling requirements to indicate that the animal was vaccinated against FMD any more than to indicate that it was vaccinated against any of a range of other diseases.
Equipment / Chemicals required and Suppliers
  • Emergency mass vaccination is best carried out using high-potency vaccines which give effective vaccination within a short time (a few days).
    • The response to an initial vaccination depends on the dose of antigen used. High potency vaccines are essential for use in emergency situations (J16.22.w1).
    • High-potency vaccines can protect cattle and pigs within a few days (e.g. by four days after vaccination) (J70.12.w1, J70.16.w2).
  • Sufficient vaccine would be needed to vaccinate all animals within the designated vaccination area.
  • Suitable concentrated inactivated FMDV vaccines are stored in vaccine banks such as the International Vaccine Bank at Pirbright and the European Vaccine Bank.
  • Commercial vaccines, less highly concentrated, may also be used; however a second dose of vaccine must be given after 3-4 weeks.
Expertise level / Ease of Use
  • Basic training required for carrying out vaccination correctly and to recognise the need biosecurity measures, particularly disinfection, to minimise the risk of vaccination teams spreading virus from one premises to another.
  • A higher level of training would be required in and around an Infected Area to ensure that vaccination teams fully understood the risks of transferring FMD virus between premises and the importance of disinfection between premises as for Ring Vaccination and Protective Emergency Vaccination..
  • In an Infected Area, inspection of the animals on each premises by a veterinarian prior to the start of vaccination of the herd/flock would be important to detect clinical FMD, as with Ring Vaccination, "Damping-down" Emergency Vaccination and "Protective" Emergency Vaccination.
Cost/ Availability
  • Sufficient vaccine to complete an emergency mass vaccination programme, or stored antigen from which vaccine may be prepared, may not be available immediately.
Legal and Ethical Considerations The use of vaccination may be restricted legally within a region or country.
Author Debra Bourne
Referee Suzanne I Boardman
References

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