Thanks for all the advice. I was pretty confident there would be no problem based on the reponses and especially the fact that I was coming in from the US, not Colombia. The agent didn't page through my passport at all, and there were no questions re: Yellow Fever countries on the entry paper work.

As for getting the shot for my own safety, I was in Medellin, Colombia, at a medium altitude, in an upscale neighborhood. I never heard or felt a mosquito. No one I met ever mentioned mosquitos or Yellow Fever. I have friends that have been many times, including to other, more remote places. They had never heard of the requirement. Just because Brazil has a specific requirement, doesn't mean that my particular trip put me at risk. If I thought I was at risk, I would have gotten the shot, even if I weren't going to Brazil.

As for getting it in one day, I barely had time to finish up work, pack, pick up a few things and make personal arrangements. My guess is that getting the shot would have involved hours of driving and hours of waiting. I'm in a far south suburb.

By getting the advice from Flyertalkers, I felt pretty confident that I wouldn't have a problem. This is a one time problem for me, as I'll check more carefully in the future.

Thanks again for all the responses.