There are about 125 strains of kennel cough and no vaccine covers all of them...in fact they take care of very few (about 25). Kennel cough is a contagious disease and is common but rarely life threatening. It is likeded to a "doggy cold". If I had to weigh the risks of kennel cough vs the risk of vaccinosis from over vaccinsting my dog, I would risk the kennel cough.
My dogs do not get Bordatella. Please research what the vaccine actually protects against and discuss the necessity if this with your vet and maybe a homeopathic vet for a second opinion. I think you will be glad you did.
A titer test can also be done before giving another vaccine to see what your dog's immunity level is.
Here is one doctor's vaccine protocola dn his views on Bordatella:
http://www.alkiswissies.com/vaccines.htm He says the vaccine only protects against 25 of the 125 strains of the disease and it basically a "doggy cold" and not that serious. He recommends against the vaccine unless you live in an area that has a particularly deadly strain and then he recommends the vaccines. Please read his article...It was copyrighted so I could not "cut and paste" here.
http://www.alkiswissies.com/vaccines.htm
Here is one story about over vaccination. It is about a cat, but is still relevant and shows the attitude of some vets.
http://www.blakkatz.com/zorro.html
Hope this helps.