There's a ton of information available about Rabies vaccinations. I'm seeing a bunch of websites that give the misguided impression that rabies has been eradicated. These are probably the same idjits that think we don't have to worry about TB, Polio or Whooping Cough any more, but recent events in the news are letting us know that indeed, we do.
Rabies is a public health threat, since it's one of the few diseases animals carry that can be given to humans. Rabies is fatal. This is where animal control and state health laws come in. Licensing requires a rabies vaccine. Some jurisdictions are also requiring that cats be licensed.
There is no difference between a 1 year and a 3 year rabies vaccine. It is mandated by the state (NOT the vet's office) how long a rabies vaccine may be good for. It varies by state but a rabies vaccine is good for one year when given to cats, puppies (4 months of age is the youngest) and adult dogs with an unknown history. So, if you have a dog that is getting it's first rabies shot, that's good for a year, after that it's good for 3 (or whatever your state dictates).
Most states require that a rabies vaccine be administered by a licensed vet, so you can't buy the rabies vaccine from an online store or vet supply.
Generally it's recommended that cats get yearly rabies boosters because outdoor cats, being allowed to roam wherever come in contact with wild animals that may expose them. Indoor cats should also get rabies vaccines as some of the critters that sneak in the house may not have read the memo that rabies is supposed to be eradicated. You may not choose to get your indoor cat vaccinated yearly, but for cripes sakes, get it done periodically. At an efficacy rate in the high 90s for the rabies vaccine, wouldn't you rather have some peace of mind?
When your pet gets a rabies vaccine, if it needs to be licensed, you get a rabies certificate. This is a legal state document. Make sure you check it out before you leave, and if there is a mistake, take care of it before you leave. I had a long headdesk conversation with a man who had his dog vaccinated for rabies 2 years ago and just realized his certificate was only good for one year. Despite his pissing and moaning, I can't go back and change that document after all this time. It could have been done within a few days. So check it before you leave.
If your dog has an illness that makes any vaccination life threatening, or is pregnant, you can still obtain a license. As your vet about an Anti Rabies Innoculation Certificate.