It depends and where you are coming from and where you are going to. Do the countries have yellow fever?
Google " countries that require yellow feaver shot" and you will find the latest.
These days most docs do not stock the shots or keep up on them. In florida the county health departments keeps the shot on hand and keep up with country requirements. They have a clinic and you will pay for what they give.
Have a wonderful time on your travels!
I believe the yellow fever vaccine is only for travel in certain remote provinces in Brazil, mostly the remote western Amazonian regions. They are not required to visit Rio or Sao Paulo, to the best of my knowledge. I know it is not required for Argentina, Chile or Peru as I've visited those countries several times.