Age is also a factor: South Africa has an age pyramid like a pyramid (elderly population 5.6%), the US has an age pyramid like a ton (elderly population 17%).
Good point.
Vaccines are also a factor: Omicron loves vaccinated people if the vaccination is old (3-4 months), that's why they do the booster drive:
I already addressed this. This is a screenshot from the study in the article.
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