THE CASE FOR A CHANGE OF POLICY TO UTILISE VACCINATION IN THE STRATEGY TO CONTROL FOOT AND MOUTH DISEASE

During the last week we stated our opinion that relying solely on the slaughter of animals to control the spread of FMD was not working. We argued that a more flexible strategy utilising vaccinations was called for. Since then we have received many messages of support but also some criticism. It seems to us that most of this criticism is based on a misunderstanding or an outdated view of the possibilities of vaccination against FMD.

This is such an important issue that we have prepared this document to fully explain and present the case for vaccination.

What is wrong with the current policy?

1. The disease is simply too infectious under British conditions in high density stock rearing areas for control by slaughter policy, especially where the authorities have proven unable to match the short recognition to slaughter interval used in the 1967-8 outbreak (almost all cases being slaughtered within 2 days). The speed of response in many cases can be seen to have contravened article 5.2(a) of Directive 85/511/EC, which requires slaughter and safe disposal of the carcasses "without delay" and with no risk of spreading the virus. If the authorities are "overwhelmed" in this process this is seen as an indication for the use of vaccination (European Commission, 1999).

Council Directive 85/511/EEC, 18th November 1985 (legislation in force 17th March 2001)
European Commission, 1999. Strategy for Emergency Vaccination against Foot and Mouth Disease (FMD). http://europa.eu.int/comm/dg24/health/sc/scah/index_en.html

2. The authorities have mistakenly used the stated incubation period in the Office Internationale des Epizooties (OIE) Animal Health Code of 14 days in their predictions of effectiveness of their policy. This figure of 14 days refers to the maximum incubation time, a figure needed in the quarantine of premises, and is far longer than the interval between infection of one animal and its ability to infect another (the generation interval). The latter is lower in sheep than other stock, therefore the rapidity of the slaughter response has to be faster than that of the 1967 situation to be effective. Since sheep with type O strain (as occurs in the current outbreak) are infective for other sheep and pigs in less than 4 days and as many as 25% were infectious at 2 days (Donaldson, 1986; Cox et al, 1998, Callens et al, 1998), the 14 day incubation can therefore mask over 3 new amplifying rounds of infection. Each FMD infected animal is estimated to initiate between 2 and 73 new infections (Woolhouse, 1996), with the lower end of this range only occurring under dry, hot conditions with low densities of stock. Situations which are far from the case in sheep flocks in Cumbria. Every delay of 4 days or more enables a new generation of infective sheep (and/or transmission to other stock) to occur.

Cox et al, 1998. Report of the Session of the Research group of the European Commission for the Control of Foot-and-mouth disease. FAO, Rome, pp139-143.
Callens et al, 1998. ibid, pp129-138.
Donaldson, 1986. Rev.Sci.tech.Off.int Epiz., 5(2), 315-321.
Woolhouse, 1996. Epidemiol.Infect., 363-371.

3. The current delayed slaughter response favours new infections, and unrecognised animals with FMD could therefore be expected to result in between 5 and 50 new infections within 7 days. Airborne spread within the neighbouring 3-5 km frequently occurred in the 1967/8 outbreak under "unfavourable" conditions on calm, warm, dry spring days and up to 100 km under cooler, moist airflows with higher humidity. The reported delays of 3-4 days from suspicion of infection to slaughter are therefore too slow to be effective in preventing longer distance spread, and establishment of infection in new areas. It must be noted that the longest recorded distance of airborne transmission occurred exactly at this time of year (the winds of March 7th and 10th), and previous longest recorded (Denmark to Sweden) also occurred at the latitudes (54-560N) of Cumbria/south of Scotland (ie climatically very similar).

Haydon et al, 1997. J. math. Appl. Med. Biol., 14, 1-9.(information also from other sources)
Donaldson, A.I. et al, 1982. Veterinary Record, 110, 53.

4. The epidemiology of FMD involving sheep is far too uncertain to have confidence that a mass cull within 3 km would be effective, or scientifically justified. In the FMD epidemic in Greece in 1994 the infection in sheep "faded out" although control measures were poorly implemented (Callens et al, 1998, Kitching, 1998). In the Macedonian outbreak of 1996, FMD infection entered sheep subclinically and as many as 50% sampled 2 years later had evidence of past infection, but again this source did not result in the outbreak perpetuating itself. Experimental studies suggest sheep produce relatively little virus for onward transmission compared to cattle, and over 1000 times less than pigs (Sellers, 1971) and are often poor at perpetuating infection by contact. The cull of sheep is therefore not supported by evidence whereas extremely active controls of pig and cattle infections are. However the "fade-out" scenarios mainly occurred under hot, dry conditions, (with the exception of Tunisia in 1989). Under cool, moist conditions, with overcast skies, long distance spread over land (1-100 km, beyond the restriction zones) is possible, particularly from cattle and pig sources, and has already thought to have occurred in this outbreak (Vet Record, March 9th 2001). Further, since sheep are the most sensitive species for becoming infected with virus, there is simply no information available on how many animals have become infected within or beyond the 3 km restriction zones, especially those which may have received windborne virus from the first infected pig farms. It simply cannot be concluded that infection has been restricted to areas planned for the cull.

Sorensen, K.J., & Naletoski, I. (1998). Report of the Session of the Research group of the European Commission for the Control of Foot-and-mouth disease. FAO, Rome , pp 176-181.
Callens, M., et al. 1998. ibid, pp 129-135.
Kitching, P. 1998. A recent history of FMD. J. Comp. Path., 118, 89-108
Sellers, R.F 1971. Quantitiative aspects of the spread of FMD. Vet. Bull., 41, 431-439.

5. The UK mass cull, therefore, unless it had occurred much earlier and involving all cattle and pigs in the restricted zones would be nowhere near sufficient to prevent infection in cattle and sheep beyond the 3 km radius. Since clinical screening in sheep is a poor guide to recognition (Callens, 1998, ref above), almost certainly the cull would be a temporary measure and a prelude to later larger culls in the areas beyond the 3 km restriction, and/or the later use of vaccination.
.
What are the effective alternatives?

6. An emergency vaccination strategy, with stamping out of infected cases, was vigorously promoted and financially supported by the EU and was very effective in the control of type A FMD in Albania (Berlinzani et a, 1998) and neighbouring Macedonia in 1996. The outbreaks were eliminated within 12 weeks and 3 weeks respectively. The former was the first outbreak in the region and therefore international responses were delayed. In the latter an area as large as Cumbria was involved and 120,000 cattle were vaccinated and a further 4,500 destroyed.

Berlinzani, A, Brocchi, B.,& Simone, F. (1998). Report of the Session of the Research group of the European Commission for the Control of Foot-and-mouth disease. FAO, Rome, pp166-175.
Sorensen, K.J., & Naletoski, I. (1998). Ibid, pp 176-181.

7. Emergency vaccination is an approved form of FMD control in Europe and there is significant preparedness to mount an effective vaccine based response, which MAFF and the EU has been funding for at least 15 years. A decision to use emergency vaccination is very likely to be approved without delay by the European Commission since the current outbreak meets almost all the criteria outlined in their policy guidelines (European Commission, 1999):

7.1. A high density of susceptible animals, (Cumbria, Dumfriesshire, mid-Wales and west Devon have very high ruminant densities favouring rapid transmission).

7.2. An infrastructure that is capable of rapidly deploying vaccination (we have highly motivated and technically competent farm staff used to vaccinating their own animals and hundreds of veterinarians and veterinary students available to undertake the work)

7.3. Predicted airborne spread of the virus (a situation that favours the use of vaccination). Although pig farms are less involved in the current locations, climatic conditions favour airborne spread from cattle farms, which paradoxically are not destined for the proposed cull.

7.4. A suitable vaccine exists, there are at least 500,000 doses (equal to 1,000,000 sheep doses) of type O vaccine at Pirbright, UK and about 10 million in the European Vaccine bank.

7.5. The incidence slope; new outbreaks are occurring daily (a rise to a record of 37 new cases on 17/3) and a very significant reservoir of infection is still present awaiting slaughter, capable of generating new waves of infection.

7.6. Distribution of outbreaks; widespread outbreaks are seen as an indication for vaccination (29 counties, 17th March) However the main foci could be surrounded by an immune barrier by ring vaccination, an approved EU approved strategies (see below).

7.7. Public reaction to stamping out; a significant negative reaction is seen as an indicator for vaccine use, since the reaction would be damaging to eventual control (non-compliance) and international opinion to Europe

7.8. Likelihood exists of the European Commission request for regionalisation of the vaccinated population. The position of the committee which framed the Report was that there would be no reason to refuse a request to regionalise the outbreak by vaccination if 1) the disease control measures would be fully enforced, 2) the protection and surveillance zones are subjected to strict controls, and 3) the control of movement of animals and their products is effective, each of which can be expected to demonstrably be the case with current EU opinion on MAFF's capabilities.

7.9. Another indication for vaccination is "an overwhelming of the capacity to kill and dispose of carcasses within a short time period" (ibid, p 5); patently the case in this outbreak where the delayed slaughter and disposal brings a risk of onward transmission.

European Commission, 1999. Strategy for Emergency Vaccination against Foot and Mouth Disease (FMD). http://europa.eu.int/comm/dg24/health/sc/scah/index_en.html

8. However, what the Emergency Vaccination report fails to consider is the value of prevention of virus entry into hill sheep and wildlife populations in upland areas. This should be a strong indicator for vaccination, since a huge cull, in effect total depopulation, would be needed if control by slaughter were the only option.

What are the advantages of emergency vaccination?

9. Emergency vaccination is of proven use in FMD control (European Commission, 1999, Salt, 1997). It can be used in two ways, simultaneously or separately; to create an immune barrier ("ring" or "belt" vaccination, creating immunised zones) to prevent spread through populations at risk from airborne or local spread of infection. Alternatively to "dampen down" infection within known FMD infected areas where there is a recognised urgent need to reduce virus transmission and to prevent onward spread beyond the restricted area (European Commission, 1999, p5).

Salt, J. (1997) . Vaccination against FMD. Veterinary Vaccinology, Elsevier Press. pp641-649.

10. Rapid reduction in virus circulation and new cases; as noted for Macedonia, effective and rapid deployment of vaccination reduced the total period of reported FMD cases to 3 weeks, despite over 18 villages in two districts being involved and avoided establishment in the sheep population of the region. Vaccination limited the slaughter to only 4,500 animals.

11. It is capable of enormously reducing the risk of airborne and vehicular spread to unaffected areas, vastly increasing public confidence within and outwith restricted areas in the control process.

12. Vaccination is also seen as ethically and publicly acceptable, a rational response to an exceptionally infective condition and which has a very rapid response. Public acceptance, and farming compliance would be expected to be exceptionally high compared to mass culling.

13. The activities can be undertaken by personnel who are not in short supply (as are veterinarians at present). Most farmers, with brief training and with additional support (veterinary students are one resource), could undertake the vaccination programme.

14. It enables valuable germ-plasm to be saved. The current culling policy is unacceptable for its impact on rare breeds and high genetic quality stock. Emergency vaccination can enable this to be mitigated. Present recommendations under the rapid system (3 months) for regaining FMD freedom require that vaccinated animals be slaughtered. This would give a short opportunity before slaughter to enable germ-plasm (particularly semen) to be collected and stored. This could be tested, with internationally approved tests recommended for FMD freedom in germ-plasm, and later used in re-establishment of the breed line. If vaccinated animals were not slaughtered, a 12-month period would need to elapse after the last case before international recognition of export trade.

15. An effective vaccine is available and approved for emergency use

15.1. Two banks of vaccine for emergency use occur in the UK, the International vaccine Bank and the European vaccine bank, both held at Pirbright (the latter bank has also deposits of vaccine in 3 other countries). These banks have 0.5 million and 10 million cattle doses of suitable O type available, which translates to about 22 million sheep doses.

Callis, J.J (1997). Problems of vaccine distribution (vaccine banks). Veterinary Vaccinology, Elsevier Press. pp703-704.

15.2. The aim of vaccination is two-fold. To protect stock against the disease and to vastly reduce the proportion of animals which could amplify virus to a point where it is unable to create new cases and naturally dies out.

15.3. The proportion of each flock herd to be effectively immunised must be at least 70%, but preferably 80% (Salt, 1997; and Professor Ahl, Tubingen, formerly Chair of EU Animal Health and Welfare Ctte, FMD Emergency vaccination working group). This is a very achievable figure in the UK where very high compliance is expected. In such an emergency as this it would be expected that UK farmers would be anxious to achieve near 100% vaccination rates.

Salt, 1997, reference above.

15.4. These emergency vaccines have a high "payload" in order to be rapidly effective as a single dose. They have been shown to be effective as early as 3 days after immunisation, in prevention of infection and disease. Within between 4 and 7 days all immunised cattle and sheep are prevented from becoming "amplifiers" capable of onward transmission. (Cox et al, 1998, Salt et al, 1997). This period is shorter than the period between the proposed cull and the expected start of the slaughter!

15.5. Further high payload vaccines are considered effective against almost all strains of the virus type O, therefore expected to be effective in the UK epidemic.

Cox et al, 1998. Report of the Session of the Research group of the European Commission for the Control of Foot-and-mouth disease. FAO, Rome, pp139-143
Salt et al,1997, Vaccine 16,7, 746-754

15.6. Vaccine delivery to farmers in Cumbria would in my opinion be expected to result in near 100% vaccination rates within 5 days, and almost complete herd immunity in 10 days. A reduction in cases to nil could be expected within 3 weeks.

16. The ramifications for farmers of emergency vaccination are almost certainly better than the current culling policy; but depend on whether MAFF opts for one of the following options:

16.1. Vaccination in the restricted zones to prevent transmission and risk to surrounding areas, followed by slaughter of vaccinated animals and active cases. This would enable a return to FMD free status in 3 months under the OIE Animal Health Code (see: www.oie.int), and despite the apparent severity of the requirement that vaccinated animals would be eventually slaughtered, the latter could occur in a progressive, orderly manner. This would allow germ-plasm from very valued bloodlines to be stored for later re-stocking/breed resuscitation, and be more acceptable locally than mass culling. The vaccination could be restricted to sheep and pigs, since they have the principal risk of rapid virus amplification and disease is more difficult to detect. Fewer herds would therefore require emergency culling and the outbreak should be curtailed in 3 weeks.

16.2. Vaccination in the restricted zones, plus ring vaccination to prevent onward transmission. This is more effective at outbreak control, but if vaccinated flocks/herds would be culled the impact on "healthy" flocks would be high and apparently nonsensical. However in national terms, a return to free status would be regained after 3 months of disease freedom and after cull of the last vaccinated animals.

16.3. Vaccination as (16.2) but without culling of vaccinated animals unless FMD is diagnosed as present in the herd/flock. Under this system a return to free status would be achieved 12 months after the last case of disease. The economic loss associated with loss of the livestock trade is seen as the "strongest argument against implementation of emergency vaccination" (European Commission, 1999). However, this needs to be set against the economic loss to other sectors (tourism etc). Vaccination would hugely reduce the compensation package, greatly reduce the loss during re-stocking, and the cost of rural aid programmes after the outbreak. Importantly it would reduce the length of time from current to the last case of infection, which could be 2 months or longer (as it was in the more restricted 1967 outbreak) under the culling system or about 3 weeks under vaccination scenario.

17. How quickly could movement of vaccinated animals be resumed, once disease is controlled?

17.1. Free movement of vaccinated animals from free areas should be permitted (European Commission, 1999), and the report provides criteria for animal movement after vaccination. It can be assumed to be resumed from 60 days after the completion of the emergency vaccination provided that an effective and reliable surveillance system is in place aided by the recent tests that distinguish animals which have met virus from those which are merely vaccinated (Panina and Ahl, 1998), Working group on Emergency Vaccination, EU Animal health and Welfare Ctte, 1998).

Panina and Ahl, 1998, Working group on Emergency Vaccination, EU Animal health and Welfare Ctte, Report of the Session of the Research group of the European Commission for the Control of Foot-and-mouth disease. FAO, Rome, pp276-278
European Commission, 1999. Strategy for Emergency Vaccination against Foot and Mouth Disease (FMD). http://europa.eu.int/comm/dg24/health/sc/scah/index_en.html

18. Doesn't vaccination interfere with our FMD free status?

18.1. European policy of non-vaccination has the objective of creating a European herd that is without evidence of antibodies to FMD virus, since evidence of antibodies might indicate animals that carry infection after exposure. Since antibodies can also arise from vaccination, very considerable effort has been made in the 1990's to develop tests that distinguish antibodies resulting from vaccination from those resulting from infection. At least 5 different tests have been developed and validated (an entire European Union funded Concerted Action was devoted to this-research summarised in over 15 papers in the supplement of the Vet Quarterly, 1998, 20, suppl 2). These tests now transform our ability to distinguish vaccinated animals that have not met the infection. They can also identify the important category of those that have been vaccinated in an emergency situation and subsequently become infected upon severe virus challenge. The international recognition ("standardisation") of these tests for the purposes of international trade is ongoing, and the Scientific Ctte of the European Commission was "of the opinion that the application of NSP-tests allows for an earlier lifting of the restrictions on the movement of vaccinated animals." Changes to the Animal Health Code of the OIE in respect of testing vaccinated animals as part of the process of regaining FMD freedom, and are under consideration by the OIE, Paris. Amendment of the Animal Health code could occur within 2 months, given the strong European consensus on the use of these tests.

18.2. At worst with emergency vaccination UK exports would be curtailed for 12 months. At best the period could be as short as 3 months after the last case has been slaughtered if the OIE Animal health code was amended this spring.

Example peer-reviewed papers;
Bergmann, I.E., et al, 2000. Improvement of a sero-diagnostic strategy for FMD virus surveillance in cattle under systematic vaccination, Arch Virol., 145 (3), 473-489.
Sorensen, K.J., et al. 1998. Differentiation of infection from vaccination in foot-and-mouth (shortened title). Arch Virool, 148 (8), 1461-76.

18.3. If DG-Agriculture was to follow the recommendations of its Scientific Committee and recognise the use of the post-vaccination surveillance system, and at its annual meeting this spring the OIE was to amend its animal health code, then FMD free status could be rapidly regained by vaccinated herds without a need for culling, unless shown to be infected.

18.4. This decision could well be made in the next few weeks if MAFF pressed for it and would completely change the economic arguments (effect on livestock trade) against vaccination.

18.5. With current regulations emergency vaccination conducted by an effective veterinary service and stamping out of remaining active cases, would at worst result in 12 months loss of the export trade. Surely MAFF should consult with the NFU and other bodies to determine if they would accept this financial loss rather than the enormity of the proposed regional cull.

Go back to East Penrest