South Africa is/was a big tourist spot for Europe. Secured resorts, mostly, I think. I'm not sure if it still is. Disclose saying they're not letting pax off a SA originated plane in Amsterdam. Don't know if it's tourists or not. Schipol is a big International hub, so connections are a concern, I bet.
Out in the bush in Africa probably not much foreign contact..
Another factor could be, speculating here, that the covid vax comes from aids research. I wonder if there is some aids exposure related covid immunity, or just general immunity stemming from a largely unvaccinated, for any disease, group.