They do have to be tested regularly though, it's nothing to with trust. You can't tell if an animal is carrying TB by looking at it, the test proves or disproves that.
This is from the MRCVS site: Cattle vaccination will not work on its own., and this from TBFree England website: There are calls for cows to be vaccinated against bTB. However there is no legal vaccine available. Currently the only option is the BCG vaccine (Mycobacterium bovis Bacille Calmette-Guérin ? ref 1,2,3,4,5). The problem is that at present it is impossible to distinguish between a BCG-vaccinated and TB-infected cow. And for this reason it is currently illegal under EU law to vaccinate cattle with the BCG jab. Work is underway to devise a DIVA test (ref 6,7,8) - a test that can Differentiate between Infected and Vaccinated Animals. But even when this has been fully developed, it will need to go through EU and international approval.
So, it's not just a question of vaccinating the cattle and leaving the badgers with TB, nor vice versa - it has to be a coordinated process limiting the disease in each animal.
As I said before, it's all very well saying "it's not worth it, it's cruel, don't do it" - what do you suggest farmers do now to reduce TB? Going vegan is never going to happen so it's pie in the sky to produce this as the answer - just saying you don't like it is fine, but it doesn't help anyone. And don't forget that all the time you say "don't cull the badgers" they are suffering too, this is from the Badgers Trust website: The disease chiefly affects the lungs and kidneys. Infected animals lose weight and body condition and experience breathing problems.
I seem incapable of making a short comment on this, I'd better go away and hide it!