Scientists say field trials aimed at developing an oral TB badger vaccine show “encouraging” results.

Candidate vaccine baits for badgers have been identified and are currently being evaluated in trials for palatability and efficacy – the degree of protection afforded to badgers that consume the bait.

However, the formulation of the vaccine is only one important element of the research, according to a review of research into the development of vaccinations against TB in badgers and cattle published in Veterinary Record.

In addition, scientists are seeking to identify practical strategies that will maximise the uptake of vaccine among the target badger population. And, as far as possible, minimise consumption by non-target species and cattle.

The review, entitled “Vaccination against tuberculosis in badgers and cattle: an overview of the challenges, developments and current research priorities in Great Britain”, says work on developing an oral vaccine has produced “some encouraging results”.

But further research on both vaccine efficacy and deployment needs to be concluded before a final candidate vaccine is ready for licensing, the study points out.

“Current research suggests that baits will need to be deployed at active badger setts in target areas to maximise bait uptake rates,” says the review.

“This relies on the locations of active badger setts to be known or surveys to be carried out in order to identify them.”

Studies have shown that badgers in bovine TB-endemic areas of the UK tended to live in group territories that contained one main sett where the majority of the social group spent most of its time.

Therefore, it is “possible” considerably less bait could be deployed at smaller outlying setts, the review suggests.

However the study stresses that an oral vaccine would only be a viable control tool if the vaccine bait and associated deployment costs were “relatively inexpensive, or less than that of the injectable vaccine”.

Deployment costs could be reduced by pre-baiting for a number of days with bait that does not contain the vaccine formulation to habituate badgers to the bait, it adds.

The safety of oral vaccine baits in non-target species, including cattle and a range of wild species – particularly rodents – must also be considered, urges the report.

“Current research indicates that deployment of bait down setts is the most likely delivery method,” says the review. “This approach would substantially reduce the risk of exposure to cattle and other livestock.”

Defra and the Welsh government have been funding research into the development of an oral vaccine for badgers since 2005.

UK government scientists are currently working with their counterparts in Ireland on field trials in the country to develop an oral TB badger vaccine .

The Animal Health and Veterinary Laboratories Agency (AHVLA) said scientists were currently focusing on generating data that would allow submission to licensing authority the Veterinary Medicines Directorate (VMD) to develop an effective, value-for-money Bacillus Calmette-Guerin (BCG) vaccine.

“We are looking at bait formulations and what works well in the field, but it will be a few years yet before an oral vaccine is ready,” confirmed an AHVLA spokesman.

“We will have to jump through a few hoops before a vaccine is licensed.”

Meanwhile, Defra has recently commissioned the design of field trials for a TB cattle vaccine. It hopes to receive EU approval for a field trial to be carried out in the UK.

However, field trials of a cattle vaccine face substantial legal and practical challenges and the adoption of a cattle vaccine without trade restrictions is not expected until at least 2023 .

Defra believes TB vaccination has an important long-term role to play in its 25-year TB eradication policy in the UK.

In the meantime, other disease control measures, including a controversial cull of badgers, are being deployed in a bid to tackle the reservoir of disease in wildlife.