My two Yorkies have only had their initial shots and haven't had any since then and they are now 14 and 15 months old. When they are around 5 years old I will have the titer test run on them to see if they are still protected. My 15 year old Chihuahua never gets shots at all. When she was just a puppy getting her puppy shots she had a seizure. That was it as far as I was concerned!
http://www.wholisticanimal.com/petvaccinations.html http://www.chron.com/cs/CDA/story.hts/front/1377004