More than a year after the emergence of COVID-19, significant regional differences in terms of morbidity persist, showing lower incidence rates in sub-Saharan Africa, Southeast Asia, and Oceania. Like SARS-CoV-1 and MERS viruses, SARS-CoV-2 is monophyletically positioned with parental species of chiropteran coronavirus. Furthermore, we observe that the spatial distribution of several targeted bat species (i.e., Coronavirus species hosts) overlaps the distribution of countries with low COVID-19 incidence. The work presented here aims to test the presence of natural immunity among population with a low COVD-19 prevalence, potentially due to a previous exposure to coronavirus antigens of a virus close related to SARS-CoV-2.

Source: (PDF) Pre-pandemic SARS-CoV-2 potential natural immunity among population of the Democratic Republic of Congo

This map is making the social media rounds. It purports to show that parts of SE Asia and Africa may have had lower Covid-19 deaths perhaps because of some unrecognized pre-existing immunity or exposure to Covid-19.  View this as speculative, someone making an hypothesis.

By EdwardM