Drugs against COVID

I've read that Chloroquine and Ivermectin are used in tropical areas, and that the rate of COVID is significantly lower in sub-Saharan Africa. This correlation could be indicative of something, if the disease rates were accurately reported. I'll stipulate for the moment that the per cohort rate is lower, but you may color me very dubious.

"Used" is a tricky word. How often are they used?

Anti-malarials aren't part of the normal weekly regimin in the malarial parts of Africa--and chloroquine isn't as useful as it once was. The link is to a study proposing monthly doses for children. When we lived there, we took one weekly.

Also, this meta-study of regular antihelmenthics on schoolchildren implies that these are not given what I'd call very regularly. Some of the studies used quarterly doses, some bi-annually. WHO advocated annual dosing.

It would seem likely that the anti-malarials or antihelmintics are only present in sub-Saharan Africans' blood periodically--probably on an as-needed basis. It isn't obvious that even if chloroquine or ivermectin provided prophylactic protection against COVID, that the residue from months before would make any difference. Desethylchloroquine has a half-life in the bloodstream of about 4 days. I'll take that as a proxy for the oral varieties. Ivermectin, per Merck, has a half-life of about 18 hours.

Maybe they help, but the correlation doesn't seem to help prove it.

On the other hand, I heard of one clinic that somebody who came in sick with anything remotely resembling malaria was automatically given an anti-malarial, on the grounds that they probably had that too. If that protocol is widely used, there could still be a relationship.

The devil is in the details--including the details of your assumptions.