Do Brasilian immigration officials strictly check for yellow fever vaccination certificate?

i am traveling only to Sao Paulo and so wouldn't normally need a yellow fever vaccination, but I am connecting in Colombia which is on their list of required countries, i actually plan on getting the vaccine, but would prefer to do it for free in Brasil instead of paying a lot of money for it here in the US, how strictly do they check for it? could i get away with not getting it and what would happen to me if i was stopped and didn't have it? thanks for any help