Interesting question: The viruses are in those areas. When individuals are tested for the antibodies, levels are found in many children. Public health resources are not as available and testing/reporting limited. It simply isn't as reported. Also, malaria is prevalent in many areas and symptoms may be attributed to that wide spread (Africa) disease. I would also guess that better climate leads to less time in enclosed spaces and less opportunity for virus to spread.

In order to know how prevalent different influenza viruses are in different locations, we need to conduct surveillance, and how much active surveillance of influenza viruses is taking place can vary greatly between different locations (as an example, this MMWR report discussed differences in influenza activity worldwide during 2018: https://pubmed.ncbi.nlm.nih.gov/30359347/ ). The WHO’s Global Influenza Surveillance and Response System (GISRS) aggregates data from different influenza virus surveillance systems worldwide to better understand which viruses are circulating where and to what degree (more info of CDC’s role in GISRS is: https://www.cdc.gov/flu/weekly/who-collaboration.htm ). Thinking about a continent like Africa, there is still circulation of influenza viruses, but seasonality can vary depending where you look (described more in this 2022 research paper: https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-022-07727-2 ).