Badger Vaccination – fact sheet on TBhub
The vaccination of badgers with the BCG vaccine was licensed by the Veterinary Medicine Directorate (the body that regulates and licenses veterinary medicines in the UK) in 2010, based on scientific evidence that demonstrated the vaccine was effective (in badgers) and safe (to badgers and cattle).
See Brown et al. (2013) for a summary of the veterinary guidance for the vaccine.
Although badger vaccination was licensed nearly a decade ago, there still remains much confusion and misunderstanding over what research has been conducted on the subject, and what the results of this research can tell us. To try and address this I was involved in producing a two page fact sheet summarising the science and answering key questions on badger vaccination.
This fat sheet is now available on the TBhub
Summarising a complicated issue like badger vaccination in two pages is challenging, and it’s not possible to cover every fact or study in detail. Although the fact sheet summarises the key questions and answers, there a couple of additional points about badger vaccination that I have highlighted below.
Lab studies on the effect of vaccination
Experimental studies involve vaccinating badgers with BCG and then subjecting them to a TB ‘challenge’ which essentially involves delivering a dose of the M. bovis bacteria directly into the badgers airway. Bovine TB is a slowly progressing disease and experimental studies generally involve small numbers of animals which can only be housed in secure facilities for a given period of time. Because of this, the challenge dose of M. bovis given to badgers is very high, to guarantee that the disease develops (so that lesion scores can be compared) in the relatively short time period of the study. As a consequence, all badgers in these studies will become in infected, but this is unlikely to reflect what happens in a wild natural setting. This is explained by Chambers et al. (2014) in a summary of badger vaccination research….
“The protection afforded to badgers by BCG in experimental challenge models such as these is rarely complete (defined as the absence of visible pathology and the isolation of M bovis from tissues), most likely because of the relatively high infection doses used in experimental studies in order to generate reproducible levels of infection. Hence the protection afforded in experimental challenge models may not reflect the level of protection afforded against ‘natural challenge’ in the wild, where animals may be exposed to lower numbers of virulent bacteria”
The effect of badger vaccination on TB in cattle
Understanding the effects of badger vaccination in cattle would ideally require a large scale field trial involving multiple areas which were randomly selected, alongside control areas with no vaccination (similar to the RBCT culling trial). To date badger vaccination has been carried in only two large areas; the BVDP (badger vaccine deployment project) near Stroud Gloucestershire and the IAA (Intensive action area) in Wales.
Cattle TB incidence did decline in the BVDP area, although a decline was also observed in comparison areas without vaccination. Unfortunately the limited size of this study (one single area) along with other factors led the authors of the report to conclude….“The factors discussed here make assessing the impact of badger vaccination on cattle bTB incidence difficult and drawing firm conclusions from the data analysed here on the impacts of badger vaccination inappropriate”.
The IAA report also suggests some evidence of a reduction of TB in cattle. However, the IAA involved multiple measures other than badger vaccination and the single comparison area chosen differed from the IAA in several ways, leading the authors to conclude “For these reasons it may not be possible to detect meaningful differences in disease trends between the IAA and the other areas for some time. Differences observed in the short term may or may not be attributable to differences in surveillance and control strategies”.
Unfortunately neither of these studies can therefore be used to generate a robust answer to the question “does badger vaccination reduce TB in cattle?”, due to several reasons clearly stated by the authors. As a consequence, the effect of badger vaccination remains uncertain.