I believe that would be sub-Saharan Africa (e.g., Uganda, Nigeria, Congo, etc) - the band of countries near the Equator. South Africa (and Botswana) are technically sub-Saharan, but far from the Equator, and they've typically been hit fairly hard by the Coronaviruses (delta, etc) - and been highly vaccinated.
The reason why the sub-Saharan countries have had low incidents of 'CoVid' cases isn't clear. Their vaccination levels are low, and they have high use of Ivermectin and/or HCQ. However, they also have a fairly young population, and the people that have survived to their adulthood have probably been exposed to a lot of 'tough' bugs - so their immune systems would be hardy. Also, they probably don't suffer from the Western disease of obesity. Soo... take your pick. They've been fairly resistant to CoVid due to their use of Ivermectin, or due to these other factors.
A FReeper speculated that because they live in a sunny climate, they may not be deficient in Vitamin D, which is purported to be helpful in avoiding COVID.