Why African countries with onchocerciasis ivermectin programs show much better COVID-19 results

Up to date, there are sixteen ivermectin studies on covid as prophylaxis. All of them validate the effectiveness in preventing a symptomatic disease.[i] The studies also underline a positive dose-response relationship. The results range from near 100% effectiveness in weekly doses to 50% in the 42-day period following a single dose. As onchocerciasis program comprises one dose every half-year, it is reasonable to think that the protection doesn’t last that long. A deeper look could give us a better understanding.

In March 2021, Japanese researchers published a study about African countries and Ivermectin on Covid-19. [ii] In the study, the authors evaluate COVID-19 outcomes in African regions. They split the countries into two groups: A group of countries with ivermectin programs to fight onchocerciasis, and another group with the remaining countries. As an aggregate, countries with the program have had a small fraction of Covid cases and deaths than the aggregation of countries without interventions.

After ruling out the age disparities, the authors concluded: “treatment with ivermectin is the most reasonable explanation”.

Undoubtedly, age is a vital factor in COVID-19 outcomes, but it is not the only one. There are other aspects to consider and cancel out before concluding in favor of ivermectin. We know more testing means more cases. Were there fewer tests in the “ivermectin group”? We know that winter affects the outbreaks, are winter in the “ivermectin group” milder? Should we analyze international travelers? Should we examine the medical system or cultural traditions?