The Wikipedia data for yellow fever IFR [0] claims that the data are based on "optimally treated patients". The problem in some of the countries where a vaccination certificate is mandatory to enter is that they do not have healthcare infrastructure to adequately treat patients. Somewhere in the past I have seen statistics that during some African yellow-fever outbreaks, 25–50% of those infected perished, which is why states were so insistent on this vaccination specifically.

[0] https://en.wikipedia.org/wiki/List_of_human_disease_case_fat...

That doesn't seem at odds with a single order-of-magnitude difference though. Covid IFR in the 0.5% range is also based on more or less optimally treated patients given a developed country's population demographics. There isn't really room for a fatality rate to be "hundreds or thousands of times higher", you run into the 100% fatal bound pretty quickly.

The Covid IFR is not in the 0.5% range, and a few exceptions notwithstanding, the fatality rate tends to be lower in developing countries than the developed world.

US covid deaths are 0.51% of the CDC’s estimated total number of covid cases. The highest (NPR) estimate of US covid deaths is 0.79% of the CDC’s estimated total number of covid cases (which is, itself, not the highest total case estimate). Many studies have estimates in the similar range.

I know the IFR is lower in developing countries, I never meant to imply otherwise.