Kennel cough vaccines and managing theoretical risks

Going back to critical appraisal (we'll go back to finish the series of "what's the point of..." various different bits of pharmacy next time), we're having a look at the risks around getting your dog vaccinated against kennel cough. Are you going to catch kennel cough from them yourself? When we say "there's a theoretical risk" what do we mean? And if we know what we mean, do the people we're explaining things to take the same meaning from what we say? How do we help people to optimise the risks they might take in a world where we don't have definite numbers to work with?