I transited GRU on the way to JNB on 14 June. I had about a 7hr stay and I was not asked for the vaccination card at any point in the process, nor did I see anyone else being questioned at the gate. That said, I don't know if they were asked upon check in at GRU, but I only saw a handful of yellow cards being flashed about so from my observation there wasn't a whole lot of concern. I also was not asked upon arrival at JNB before connecting to CPT. YMMV.