Good morning jhp, somewhere in the back of my mind is that if you have been to a country such as Brazil that you have to show your YF card if you visit certain other countries following being there.Having said that I never had to show my card in other countries.
Seems to me that since you're only transiting through Brazil why would you need it.
Hey if you do get it at least its good for 10 years!! I figure that my next one(this year) will be my last one,but maybe not since my motto is "have bags will travel"