Vaccination against bovine TB - Environment, Food and Rural Affairs Committee Contents


3  An injectable vaccine for badgers

38. An injectable BCG vaccine for badgers has been licensed for use since March 2010. Its availability is the culmination of 10 years and £11m of government research.[57] BadgerBCG does not confer complete protection from bovine TB and has no discernible effect on already infected animals. A study of infected captive badgers has demonstrated that vaccination can reduce the progression, severity and excretion of the disease. Dr Carter, Senior Scientist at FERA, told us that research conducted in the field supported this conclusion. While the field study was primarily designed to assess the safety of the vaccine and gather the data required to license BCG, the results were consistent with the clinical study.[58] The study showed vaccinated badgers continued to shed TB bacteria but to a lesser extent than unvaccinated badgers.[59]

39. Data from the study also demonstrated that the risk of unvaccinated cubs testing positive for the disease was reduced by 79% when more than a third of the adults in their social group had been vaccinated.[60] This would suggest that not every badger need be vaccinated every year for a vaccination policy to be effective—the vaccine needs to be administered only to enough of the uninfected population to establish herd immunity.[61] What is clear is that the longer the vaccination programme was maintained, the greater would be the benefit realised.

Known unknowns

THE BADGER POPULATION

40. The size and spatial variation of the badger population in the United Kingdom is largely unknown as is the level of TB infection in that population. The Randomised Badger Culling Trial (RBCT) demonstrated the degree to which the prevalence of TB can vary between areas. Within the 10 areas studied in the RBCT trial TB prevalence ranged from 1.5% to 35%.[62] Keith Meldrum, a former Chief Veterinary Officer states that 23% of the more than 13,000 badgers put down under a policy of removal in the mid-90s showed evidence of TB during post-mortem.[63]

41. A badger sett survey is currently under way, which will report this summer. The survey will provide an estimate of the density and abundance of badger social and family groups by region. A Defra-funded study planned for this winter will look at the average size of badger groups in different landscapes and parts of the country.[64] Neither study will demonstrate the level and distribution of TB in the badger population.

42. Density of population does not necessarily correlate with prevalence of disease.[65] Dr Wilson, Team Leader at FERA, thought that estimating the proportion of the badger population infected with bovine TB would be difficult but that 'measures of prevalence on their own are not particularly useful. What is more useful is looking at how they might vary either regionally or over time.'[66] Professor Hewinson admitted there was an 'evidence gap':

    We do not know whether TB is in badgers in areas where there is no cattle TB, and some of the work in Ireland suggests that there is TB in badgers in both high prevalence and low prevalence areas; it is just the level of TB in those badgers that is the difference.[67]

EFFICACY OF THE VACCINE

43. The BadgerBCG vaccine has been available only since March 2010; as Dr Wilson told us 'it is still an embryonic piece of work'.[68] Clinical and field trials have demonstrated a beneficial outcome of using the vaccine but precise efficacy appears difficult to quantify. For example, three tests used in the 2010 study by Chambers et al showed that:

    ·  Vaccination was associated with significant reductions in the incidence of positive Stat-Pak results (73.8%);

    ·  combined Stat-Pak and culture positives (61.4%); and

    ·  the incidence of IFNã test-positivity was not significantly reduced by vaccination.[69]

The study has led many to state that injectable BadgerBCG reduces positive serological results by 74%.[70] The Veterinary Association of Wildlife Management (VAWM) contest that, saying that the study was 'at best a small scale field study, which only involved 262 animals and which was presumably not designed to assess efficacy' and that while one test showed results of nearly 74%, another using the same data showed no significant difference.[71] In their written evidence Defra confirm that the study did not produce 'a true efficacy figure'.[72]

44. Since the 2010 study further work has been done reworking the original data using an additional more complex serological test. The 2012 work (Carter et al) states that the

    triple testV used here is the most sensitive and specific measure of M. bovis infection in a live vaccinated badger and so provides confidence that these results are biologically meaningful.

    The effect of vaccination on the triple testV outcome was to reduce the risk of a positive result by 54% in vaccinated individuals. Without post-mortem data it was not possible to ascertain what proportion of the triple testV-negative, vaccinated badgers were protected from infection and what proportion still acquired infection, but were not detected using the triple testV. It is unsafe to assume that triple testV negativity equates to the absence of infection. A greater estimate of vaccine effect (76%) was observed with the dual test. The IGRA (ESAT-6/CFP-10) was absent from the dual test. As the IGRA is more sensitive than either the Stat-Pak or culture at detecting M. bovis infection in live badgers, this result was not entirely unexpected.[73]

45. As with the 2010 study, the higher figure from the 2012 work (76%) is widely quoted[74] despite the more sensitive and specific test showing the effect of vaccination was to reduce the risk of a positive result to the lower figure of 54%. In order for vaccination to be considered part of a strategy to eradicate bovine TB we first need to establish what level of efficacy can be expected. The research undertaken by Chambers et al was vital in gathering the data required to get a badger vaccine licensed and available to use and we congratulate those involved in achieving this aim. To have another tool to use against bovine TB is valuable. However, what is also apparent is that substantial data clearly showing the effect of the vaccine in the field are lacking. Now that a vaccine is available the Government should consider addressing this evidence gap by researching the efficacy of the BadgerBCG vaccine in the field.

IMPACT OF A PROGRAMME OF BADGER VACCINATION ON CATTLE

46. There is no direct evidence that a programme of badger vaccination results in reduced transmission of TB to cattle. Dr Wilson described the lack of data as 'one of the most fundamental knowledge gaps that we have'.[75] Use of the BadgerBCG vaccine is still in its infancy so the lack of such data is not surprising. It is not clear how or whether the Government intends to address this problem. In its written evidence Defra state that to quantify the contribution 'it is likely we would need to carry out a large-scale field trial (on a comparable scale to the RBCT) the results of which would take many years to collect.'[76]

47. The Government currently funds a Badger Vaccine Deployment Project (BVDP) which covers 120km2 in Gloucestershire. The project was not set up as a scientific trial but exists to test the deployment of vaccination and train lay vaccinators. The BVDP was originally intended to cover six areas but five of the planned projects were cancelled soon after the current Government took office. Dr Wilson told us that the area in Gloucestershire 'is not large enough in its own right to look at statistical effects of TB on cattle herd breakdowns ... there is no doubt, however, that if all six areas had all been online there would have been more data for us to work with to start looking and addressing questions around what effect this work is having on cattle TB rates ... it is going to be more difficult from the position we are in now to fill the knowledge gap'.[77] Although they were not originally planned to test the effectiveness of the vaccine or the impact of its deployment on the incidence of TB in cattle, the cancellation of five of the six Badger Vaccine Deployment Projects represents a missed opportunity to collect valuable data on the effect of the badger vaccine.

48. The absence of empirical evidence of the impact of badger vaccination on the incidence of TB in cattle is not on its own a reason not to pursue a vaccination strategy. A vaccine that reduces the excretion of M. Bovis bacteria is a powerful tool. An effective programme of badger vaccination in areas where badgers are the suspected source of TB in cattle would be expected to reduce transmission of the disease between the species.

TRANSMISSION

49. The discovery of bovine TB in 'closed herds'[78] has led to badgers being identified as a source of TB in cattle. The strength of transmission of M. Bovis between badgers and cattle is largely unknown as is the route of transmission.[79] Dr Wilson told us:

    In the past, the feeling was that transmission was more likely on pasture, where cattle come into contact with contaminated excreta from badgers at latrines. Equally, however, we now know from research we have carried out in the last few years that badgers readily enter farm buildings. ... farm buildings represent a high risk area because we know in some circumstances badgers and cattle will come into quite close contact with each other.[80]

50. There is evidence that infected badgers tend to range further than non-infected individuals and the different behaviour pattern may increase the likelihood of the infected badgers encountering cattle.[81] Not everyone agrees that badgers are a cause of TB in cattle. In written evidence Martin Hancox made clear his view that:

    The widely held belief that cows catch TB from badger urine with 300,000 bacilli/cc is wildly improbable. Some 99% drains straight into soil; the rest is disinfected by UV in sunlight within 3 days, so a cow is unlikely to ingest the minimum dose c1million bacilli, ie 3cc of fresh urine.[82]

51. Although the extent of infection transmitted between badgers and cattle is subject to debate, we believe there is merit in gathering information on potential transmission pathways and we welcome FERA's research project on badger farm visits. Developing and implementing effective badger exclusion methods may prove more cost effective than other measures aimed at addressing the impact of infected badgers on cattle.

HERD IMMUNITY

52. A specific challenge for a vaccination policy is to vaccinate animals before they become infected. As Carter et al (2012) point out:

    This is a particular concern for the vaccination of badgers against TB because they live in close contact with one another and their young do not generally emerge from their underground den (sett) for the first two months of their life. The argument that many badger cubs will become infected during this period (i.e. before they can be caught and vaccinated), has been identified as a key potential constraint on the effectiveness of badger vaccination as a management tool.[83]

53. Analysis of evidence from the four-year field study has shown that where a high proportion of group members were vaccinated, unvaccinated cubs born into those groups were significantly less likely to test positive for TB. Dr Carter told us the most plausible explanation for this is herd immunity:[84] 'the cubs were indirectly protected because a higher proportion of the badgers they were coming into contact with over the course of the study had been vaccinated and had at least received some form of protection from the vaccine.'[85] Results from the field study showed that when more than a third of the social group had been vaccinated the risk to unvaccinated cubs was reduced by 79%.[86] However, Dr Carter explained that owing to a range of factors including prevalence of infection, population density, and other environmental factors, 'we cannot say what proportion of the population you would need to vaccinate to achieve herd immunity'.[87]

54. Herd immunity is a sought after outcome of any vaccination programme. It means transmission of disease is reduced and non-vaccinated animals are given a measure of protection reducing the need for further deployment of the vaccine. The identification of the indirect effect of badger vaccination on unvaccinated cubs is an important step forward in research on the effectiveness of the BadgerBCG vaccine. For herd immunity to occur, a significant proportion of the uninfected badger population must be trapped and vaccinated. The precise numbers depend not only on local factors such as badger population, density and environmental factors but, as importantly, on the efficacy of the vaccine. While herd immunity may mean that not every badger has to be vaccinated every year, we need to be confident, without testing each badger, that herd immunity has developed. Further research on the indirect effect of vaccination is therefore necessary and must be included as part of future evidence-gathering on the efficacy of the vaccine in the field.

Cost

DEPLOYMENT

55. Vaccination of badgers is expensive. Defra's current best estimate of the cost of trapping and vaccinating badgers is £2,000-£4,000 per km2.[88] Costs can vary according to factors such as ease of access to setts, terrain, weather, time of year and experience of personnel. The cost will also depend on factors such as the size of area being vaccinated, density of badgers, frequency of vaccination, and model of deployment. Fixed costs include the vaccine itself, fridges (as the vaccine needs to be kept in cold conditions at all times to remain viable), disposables, traps, vehicles and training. However, as Dr Wilson told us, the largest cost is manpower:

    A badger vaccination round on a farm or something like that would involve a survey, the deployment of the traps—i.e. putting or digging them into place—and then perhaps several days of pre-baiting the traps, which involves repeated visits by staff and operatives going back, with the traps locked open, putting bait in them and getting the badgers used to going in them for food rewards. The final step is to set the traps, go back, check the traps the morning after setting them, vaccinate the animals and release them, and then remove the traps and clean up. That can be a two or three­week programme. Obviously, if you are talking about manpower for that length of time there is clearly a significant cost associated with that.[89]

Research by the NFU has indicated that even where farmers pre-baited traps on their own land, the cost of vaccination still amounted to £1,736km2.[90]

56. In 2012, work undertaken by FERA, the Welsh Assembly Government and a number of NGOs led to more than 2,500 badgers being vaccinated.[91] A dozen wildlife organisations now actively deploy the vaccine in England. Although vaccination is costly, scope exists for economies of scale but this will need a more coordinated national approach to badger vaccination to enable equipment and information to be shared more effectively. There is great enthusiasm among voluntary organisations for deploying the badger vaccine. The Government should not miss the opportunity to use them both to gather evidence and as a resource to carry out vaccination. A first step should be to set up an advisory service to help NGOs plan and deploy a programme of vaccination and to advise what data it would be useful to obtain.

IDENTIFICATION AND SURVEILLANCE

57. Better targeting of resources is key to reducing the costs of a vaccination programme. Collaborative work undertaken by the University of Warwick's School of Life Sciences and the Government (Travers et al 2012) suggests that Polymerase Chain Reaction (PCR) tests on faeces in badger latrines can determine whether inhabitants of the related sett are infected with bovine TB. While the PCR test will not identify which individual badger has TB, such tests may, when fully developed, prove useful in identifying which setts harbour infected badgers.[92] The research concludes that 'field studies are now required to determine how best to apply the assay for population-level bTB surveillance in wildlife'.[93]

58. Another option is to test captured badgers for infection, releasing only those which tested negative. However, as the BVA made clear, this option could make the problem worse:

    the diagnostics for badger­side testing have a low sensitivity of about 50%. So arguably, in simple terms, for every two infected badgers that are trapped and tested, one will be vaccinated and released and one will be culled and removed. So we still have the disturbance in the badger population from that proportion that has been culled. That can create perturbation. What you have actually done is release infected badgers back into that perturbed population. Potentially you could make the perturbation effect worse than removing badgers on a pure culling exercise alone.[94]

59. PCR testing of badger faeces has the potential to identify those setts which harbour infected badgers. Doing so will not only enable a vaccination programme to be better targeted and therefore more cost-effective but may also be able to show whether the vaccination has been successful in creating herd immunity in particular social groups. We recommend that the Government provide funding to explore how this research might be applied practically in the field.

TRAINING

60. Vaccination can be undertaken only by trained vaccinators. The Government has made up to £250,000 a year available over three years to support and encourage badger vaccination.[95] The scheme is aimed at supporting vaccination in the cull pilot areas and to subsidise lay vaccinator training and certification costs for voluntary and community organisations only.[96] Brock Vaccination and the NFU considered that the allocation of funding resources might be better targeted if farmers who wished to undertake the vaccinator training were also eligible for support. We agree. Farmers are not entitled to funding to complete the lay vaccinator training course despite it being their land on which access is required to undertake the vaccination. This is perverse. The Government should amend eligibility for the course to include farmers.

61. Gloucestershire Wildlife Trust report that training capacity for lay vaccinators and subsequent certification and licensing is a limiting factor for any significant increase in voluntary deployment: 'in 2013 there are only 50 places on the FERA training course, with 10 places available per course.'[97] The Government should increase the number of places on its lay vaccinator training course. It would be disappointing if a lack of qualified vaccinators became the limiting factor in a programme aimed at reducing TB in badgers.

Strategy

62. If cost-effective, a programme of badger vaccination will undoubtedly meet greater support and public approval than culling. It would be unlikely to be subject to public protest and disruption and, while trapping brings with it welfare concerns, a programme of vaccination is more likely than other options to result in a healthy badger population. There is also no evidence of the perturbation effect that is attributed to culling. The efforts of wildlife NGOs, the Welsh Assembly Government and FERA have demonstrated that deploying an injectable vaccine, while expensive, is feasible in limited areas. However, it remains the case that vaccination does not remove and has no effect on already-infected badgers. Indeed, mitigating the effect of the disease through vaccination may increase the survival time of carriers and secretors.[98]

63. Benefits from vaccination would be expected to accrue incrementally over several years as the number of badgers vaccinated increased and infected badgers died off. Although, according to Defra, most individual badgers already infected with bovine TB will die off within five years, it is likely that annual vaccination would need to last many years more to be successful.[99] For vaccination to produce herd immunity, a significant proportion of badgers need to be captured. The Carter et al research suggested that vaccination reduced the risk of a positive test result by 54% in vaccinated individuals. However, if only 50% of badgers were trapped and vaccinated with a vaccine that is 54% effective then just a quarter of the badger population would have a reduced risk of infection - and that is assuming that those vaccinated were not already infected. The more endemic the disease the more difficult it will be and the longer it will take for vaccination to be effective.[100] The Government needs to undertake further research in order to have confidence in the level of efficacy to be expected from the vaccine when deployed in the field.

64. The development of a vaccine that reduced the level of infection in badgers would be a valuable tool in the battle against bovine TB but, despite 10 years of research and £11million spent in development, it is one that Defra lack a strategy for using. A number of voluntary organisations are deploying the vaccine and, while we commend their actions, in the absence of a clear nationally coordinated strategy this work can only have a limited impact on the wider problem of bovine TB. We are particularly concerned that Defra may miss the opportunity to make use of the enthusiasm that exists in the voluntary sector for badger vaccination.

65. Badger vaccination is expensive and no magic bullet. We agree with the Wildlife Trusts that if it is going to make a difference, it needs to be deployed strategically in areas where it is likely to have the biggest impact. The vaccine has been available for use for more than three years. Having developed the vaccine, Defra must now produce a clear strategy for its use.



57   Ev w2 [RSPCA] Back

58   Q 15; Chambers et al, Bacillus Calmette-Guérin vaccination reduces the severity and progression of tuberculosis in badgers, Proceedings of the Royal Society: B, 22 June 2011, vol. 278 no. 1713 1913-1920, available at http://rspb.royalsocietypublishing.org/content/278/1713/1913.full Back

59   Ev w29 [VAWM], Q 15 and Carter SP, Chambers MA, Rushton SP, Shirley MDF, Schuchert P, et al, BCG Vaccination Reduces Risk of Tuberculosis Infection in Vaccinated Badgers and Unvaccinated Badger Cubs. PLoS ONE 7(12): available at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0049833 Back

60   Ev w20 [Humane Society] and Carter et al study Back

61   Ev w22 [RSPB] Back

62   Q 14 Back

63   Ev w19 [Keith Meldrum] Back

64   Q 13 Back

65   See written evidence from Martin Hancox, Ev w8, for further discussion on this subject and Bovine Tuberculosis in Cattle and Badgers: Report to the Rt Hon Dr Jack Cunningham MP by Professor J Krebs and the Independent Scientific Review Group, p46 Back

66   Q 14 Back

67   Q 313 Back

68   Q 52 Back

69   Chambers et al, Bacillus Calmette-Guérin vaccination reduces the severity and progression of tuberculosis in badgers, Proceedings of the Royal Society: B, 22 June 2011, vol. 278 no. 1713 1913-1920 http://rspb.royalsocietypublishing.org/content/278/1713/1913.full Back

70   For example, Ev w27 [Network for Animals], Ev w42 [British Veterinary Zoological Society], Ev w50 [Secret World Wildlife Rescue] Back

71   Ev w29 [VAWM] Back

72   Ev 70 [Defra] Back

73   Carter SP, Chambers MA, Rushton SP, Shirley MDF, Schuchert P, et al, BCG Vaccination Reduces Risk of Tuberculosis Infection in Vaccinated Badgers and Unvaccinated Badger Cubs. PLoS ONE 7(12): available at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0049833 Back

74   For example, Ev w20 [Humane Society], Badger Trust press notice 18 December 2012 http://www.badger.org.uk/_Attachments/Resources/776_S4.pdf Back

75   Q 38 Back

76   Ev 70 [Defra] Back

77   Q 23 Back

78   In this context a closed herd is one without contact with cattle from outside the herd. Back

79   Q 42 Back

80   Qq 43-4; FERA told the NIA Agriculture and Rural Development Committee that 'Of the 32 farms [studied], 19 had visits from badgers. Some of those had only one or two visits recorded over the whole year, but at the other end of the scale, about 10% of the farms had visits on 70% to 80% of nights. Badgers came on five or six nights a week. It was not just one badger, it was not just one incursion a night, and they were not just travelling through the farmyards; they were going into the farm buildings'. See Northern Ireland Assembly Agriculture and Rural Development Committee Report, Review into Bovine Tuberculosis, paras 105-109 for further discussion of badger visits to farm buildings. Back

81   Ev w31 [Society of Biology] and Qq 44-5 Back

82   Ev w8 [Martin Hancox] Back

83   Carter et al study, 2012, see earlier footnote for full citation Back

84   Herd immunity occurs when the vaccination of a significant proportion of a population provides a measure of protection for individuals that have no immunity. It arises when a sufficiently high percentage of the population is protected through vaccination to disrupt chains of infection and therefore stop the spread of disease. Establishing herd immunity is therefore a sought after outcome of vaccination policy. Back

85   Q 20 Back

86   Ev 70 [Defra] Back

87   Q 20 Back

88   Ev 70 [Defra]; Gloucestershire Wildlife Trust published a cost range of £41-51 per hectare for their work in 2011 and provide a detailed breakdown of costs in their report Nature Reserves Badger Vaccination Deployment Programme 2011, while the Welsh Assembly Government's project cost £3912 per km2 in its first year. Back

89   Q 31 Back

90   Ev w51 [NFU] Back

91   Ev w22 [RSPB]; In the first year of the Welsh Assembly Government's five year vaccination programme a total of 1,424 badgers were vaccinated over an area of 288km2 at a cost of £943,000. Back

92   Ev 46 [IFAW]; Travis ER, Gaze WH, Pontiroli A, Sweeney FP, Porter D, et al. (2011) An Inter-Laboratory Validation of a Real Time PCR Assay to Measure Host Excretion of Bacterial Pathogens, Particularly of Mycobacterium bovis. PLoS ONE 6(11). Similar work, funded by Defra, is also being undertaken by Queens University Belfast. Back

93   Ibid. Back

94   Q 252 Back

95   Defra website, https://www.gov.uk/government/news/update-on-measures-to-tackle-bovine-tb and Ev 70 [Defra] Back

96   Defra are providing funds to cover 50% of the cost of becoming an accredited and certified lay vaccinator. Farmers are not eligible to apply for funding from this scheme to train as vaccinators. To date, Fera have trained 137 lay vaccinators on the Cage Trapping and Vaccination of Badgers course. Back

97   Gloucestershire Wildlife Trust Nature Reserves Badger Vaccine Deployment 2012 available at www.gloucestershirewildlifetrust.co.uk Back

98   Ev w17 [Ian Kett] Back

99   The British Cattle Veterinary Association has referred to a timescale of 12 years and Paul Livingstone, Technical Manager of the Animal Health Board in New Zealand,has referred to a timescale of 20 years - see www.bovinetb.info for further discussion. Back

100   Options for the use of badger vaccines for the control of bovine TB, Defra Back


 
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