When Abbey got her first rabies shot at 6 months she was sick for several days afterward. Then she had a seizure and had to go to the emergency animal hospital. Her liver enzymes were elevated as in hepatitis! The vet swore he'd never seen hepatitis after rabies vaccination. In my state yearly vaccination is required but and this is the part I don't understand vets can give the 3 year dose if they choose to. That's what the vet did without telling me! We have a new vet now who knows her history and he gives the one year dose then watches her for several hours. No problems since.
Okay want to get even madder? MANY vets use ONLY the 3 yr vaccine but you pay one price if you ask for 1 yr, another for 3 yr, and they tag accordingly! When i first read that I had a fit, but its common.
Anyway, I give pups the one year shot, then go with the 3 yr the next time. I can't tell you if its rational, but I just like to keep the amounts down til they are mature.