mine have never been vaccinated but never go into kennels. That say, my collie cross caught it about 4 years ago, but there was a bit of an epidemic in our village cos some kind person kept on walking their dogs with other dogs even though they knew their dog had kennel cough (unfortunately i didnt find out until it was too late). Given that she was 12 at the time she coped with it really well, so suspect she only had a mild version.
Our vet has never even suggested it as she knows i never put them in kennels
