I thought they only got it when boarded. At least that's when mine used to get it before I realized it was cheaper to have someone stay at the house while gone than to pay to board the animals.
My Blue dawg (pictured in my avatar) is epileptic. He hates kennels and crates, so we always get someone to stay at the house. It's a lot cheaper than paying to board 3 dogs.
I always get the drops to protect against kennel cough. I don't board the dogs, but they do go to various greyhound events and always have to greet the other greys. My vet said it's safest that way.
BEG, I believe the protection should have lasted a year. Hope he gets better soon, poor pup.