I looked this up for Namibia but SA not a risk country so  see that is would be required coming from Lisbon going through several Central African countries but not SA: Required if traveling from a country with risk of YF virus transmission and ≥9 months of age, including transit >12 hours in an airport located in a country with risk of YF virus transmission.1   This list of risk countries https://wwwnc.cdc.gov/travel/yellowbook/2020/travel-relat