Wow, I had no idea that the Yellow Fever vaccine was controversial! I had to have one to travel to Peru in 2006 (I was 50 at the time), it was easy to get by appointment at the local travel clinic (in a town of 10,000), I think it cost around $150 (my health insurance covered it) and the vaccine certificate of proof was stamped in my passport and off I went, without any issues.

So there is certainly precedence with countries requiring a specific vaccine for entry.