You might want to check with Ngaire on this. Her advice in the past is "get the shots". And in fact, our consulate website states that you have to bring the certificate with you when you apply for a visa.
We have to get them, since we're transitting thru Panama. That's on the list of countries which, if you have visited them within a certain timeframe, Brazil demands the shot. This seems to contradict the above, so who knows who's correct.
