from what I understand the one year vaccine is the same as the three year vaccine. It just depends on how often it is lawfully required.
I know for a fact that in wv you have to get your dogs vaccinated against rabies every two years. Unless it is a pup and then you have to revaccinate a year later. But if I go over to Maryland and have a Maryland vet vaccinate my dogs it is good for three years........but since I live in wv, the three year vaccination is only good for two years, so I must get it again at the two year mark. Unless it is a pup, then I have to get it again at the one year mark.
I have real reason to believe that all the rabies vaccinations last up to three years, but depending on where you live, and severity of cases, and the law, it is thought to be different shots, but in reality are all the same.
So in reality the "one year shot" is the same as the "three year shot". I did question a vet on this and would not give me a direct answer. They just have to follow laws and therefore it seems like a one year shot would be less damaging than a three year shot, but what they give around here are all one in the same.
Now it might be different other places, but I have compared the one year shot that Rocket got, and the 3 year shot that Charlie and Shiloh got and there was no difference. Although Charlie and Shiloh, because of our laws will need another in two years not three. Very confusing but it helps to do a little research for rabies vaccines in your area.