TB is a very difficult infection against which to develop vaccines. Huge efforts have and are being made to develop new vaccines particularly against human TB. While progress is being made to develop new vaccines, currently the only vaccine available for clinical use in humans is BCG which was developed more than 100 years ago. This illustrates the huge challenges in developing TB vaccines.
A TB vaccine would be an assistance in the fight against TB. While the use of a vaccine will not cure an animal that already has bTB, the vaccination of cattle could prevent disease in a herd and also prevent the transmission of disease between herds.
BCG is a weakened (attenuated) strain of bTB. It is known to be protective against TB in both humans and cattle. However its efficacy (ability to produce the desired effect) does vary and the reasons for this variation are not fully understood. Nonetheless it could provide very useful protection against bTB in cattle. Unfortunately its use is currently precluded in NI as vaccinated cattle will also test positive with both the skin test and the interferon-gamma blood test. In other words it would be impossible to differentiate infected from vaccinated cattle. This would have a very substantial negative impact on the NI bTB control programme and on the international trade of animals and animal products. It is therefore currently prohibited from use.
There is work ongoing to develop a novel test that could differentiate infected from vaccinated animals. This is still undergoing validation and is some way off becoming a viable option for farmers. Two key areas that will need to be addressed before it could be considered for use are:
- that the test consistently works in differentiating infected from vaccinated cattle with a high level of accuracy, and
- that the test is accepted under trade rules as a recognised diagnostic test.