I'm curious about this as I was reading another web site that claimed they weren't. The claim was that a dog's immune system works similar to ours so that once they've had all their shots they're pretty much set for life. The site also claimed that vets recommend yearly shots because up until recently, that was the standard but now it has changed. They also said there are some vets who recommend the shots just because they make a fair ammount of money off of them. I must confess the logic kind of made sense. I don't get a measles shot every year and I'm still immune to the measles (I hope). Are dogs immune systems that much different from ours?