The vaccine is completely useless if the dog already has the disease. You should also be aware that your dogs are not completely protected. Kennel cough has many strains. Vaccinated dogs are protected against only that strain in the vaccine. They can still get a different one--just like your flu shot only protects against certain strains of the flu not all of them! Keep them well away from the infected dog. Kennel cough is airborne so if this is a close neighbor isolation may not be possible. My dogs all caught it two years ago from a kennel over a mile away--course every sled dog yard for 100 miles had kennel cough that spring!