The article did mention a younger aged population with fewer elderly. Perhaps sunshine and more time outside also help.
The thing is, even in those areas where river blindness or elephantiasis is endemic and ivermectin is used, it’s only taken one time, once per year, sometimes twice per year.
For maps where it is taken, vs Covid rates see here:
https://freerepublic.com/focus/news/4015279/posts?page=30#30
See also:
https://freerepublic.com/focus/f-news/4015279/posts?page=34#34
Yes, I agree about the sunshine and younger population. Also, fewer people in climate-controlled buildings and shopping at outdoor markets. And no nursing homes.