Why vaccinate badgers against TB?

Why vaccinate badgers against TB? It is not a cure, there are no field studies to show how effective it will be and isn’t it just as expensive as culling?

We will attempt to answer some of those questions below.

badger by Andrew Mason

badger by Andrew Mason

It is quite right that there has been no field study of the impacts of vaccination equivalent to that done for culling (the £50m Randomised Badger Culling Trial, RBCT). As such there is no robust field study that shows the extent to which the vaccination of badgers can and would impact the extent of TB breakdowns under different conditions in the field. There are many, many potentially confounding issues which is why the RBCT cost so much itself, and despite all that time and money remains criticised by some for its robustness.

What we do have, however, is a mixture of laboratory and now field evidence as well that shows beneficial effects of the vaccine on the epidemiology of the disease within the badger population. This includes:

(1) In a clinical field study, BCG vaccination of free-living badgers reduced the incidence of positive serological test results by 73.8 per cent. (Chambers, MA et al. (2010) Bacillus Calmette-Guerin vaccination reduces the severity and progression of tuberculosis in badgers. Proc. R. Soc. B , published online)

(2) A second paper showing that as well as the above protective effect, there was an impact on unvaccinated cubs; that when more than a third of the social group of adult badgers is vaccinated the risk to cubs reduces by 79%. (Carter SP, Chambers MA, Rushton SP, Shirley MDF, Schuchert P, et al. (2012) BCG Vaccination Reduces Risk of Tuberculosis Infection in Vaccinated Badgers and Unvaccinated Badger Cubs. PLoS ONE 7(12): e49833. doi:10.1371/journal.pone.0049833)

We also know from the first year of Welsh Government’s programme that cage trapping and vaccinating- whilst less ideal than an oral bait vaccine for example, until that is available- is feasible. Just as feasible as cage trapping and shooting- and slightly less expensive as there are no costs associated with carcass disposal and testing (or for that matter, policing the kind of civil disorder currently evident in England).

We would agree absolutely that in an ideal world we would have a field trial on the scale of the RBCT to assess the impacts of vaccination. Unfortunately we know that this won’t be accepted – partly because of the current financial climate, and partly because of the political perception that we need to be ‘seen to act’ now rather than delay with another programme of this nature, which could take ten years, and as with the RBCT, still be criticised and not accepted by all.

Badger by Margaret Holland

Badger by Margaret Holland

Defra and FERA were running the Badger Vaccine Deployment Project (BVDP) which would have gone some way to answering the questions about impact on cattle disease, but tragically cut funding to it, reducing their study areas from five/six to just one, meaning that whilst it will contribute to the evidence base for feasibility and impact on badgers it is not likely to tell us anything meaningful about the follow-on effect  on cattle. Likewise the Welsh Government’s action in north Pembrokeshire is very much a ‘treatment’ and will not tell us anything quantitative about the impact of vaccination because there are too many other variables that are also different in this area, confounding the results, such as stricter cattle measures.

The principal reasons why the Wildlife Trusts and WTSWW are supporting vaccination is that we believe it is the only sustainable way of tackling the disease. Culling, IF it meets the criteria, can result in a modest reduction in breakdowns; 16% is the best reduction anticipated. However because it targets badgers and not the disease, ultimately it does not address the reservoir of the disease in the badger population. In fact Rosie Woodroffe’s analysis from the RBCT data showed that in some cases the prevalence of the disease in the remaining badgers increased, another result of perturbation, even though total number of badgers (and therefore TB breakdowns) reduced in the short term. Therefore there is no exit strategy other than keeping badger numbers low in perpetuity, which would be very difficult to do whilst maintaining the strict conditions required to avoid perturbation and spread the disease.

Badger by Jon Hawkins

Badger by Jon Hawkins

Culling could actually make future vaccination more difficult. If the remaining badgers, with the same or greater disease burden, form the founding members of a recovering population, then clearly we are not any better off than before. We are also clearly very concerned that the risk of failing to meet the conditions required to reduce TB breakdowns will NOT be met and the cull will be in vain.

We appreciate that there is less evidence to quantify the impact that vaccination will have, and in better circumstances we would absolutely be lobbying for an appropriate field trial. But we know that vaccination WILL reduce the disease burden in the badgers, and that it won’t cause perturbation and carries no risk of worsening TB in cattle by that route. It will also protect badgers from contracting the disease from cattle, thereby reducing the impact of the disease in the wildlife reservoir.

Therefore there is an element of balancing unequal evidence and risk between the approaches, we hope this clarifies our position, which ultimately could be summarised as ‘do no harm’, with a strong eye to the future, and being serious about eliminating the disease. Ultimately vaccination is the only way of actually removing the disease from any population that does not involve exterminating the host as well.

Find out more about what we are doing to tackle the disease.