Some might not be worth it as you are required to have the yellow card when you check in. If you don't have it, they will cancel your segments as it is illegal. The yellow fever shot is above $200 in the USA and needs to have at least a few days ahead of your scheduled flight. Had it done last year for my Brazil/JNB trip. Plus, if you are from the USA, some might not even know that we can enter Brazil now without a visa, coming back from JNB into Brazil as the book/manual that they have is not yet updated so you will to seek a supervisor if the security check is confusing for them to understand.