there are different kinds of ace2 receptors in humans, scattered across various ethnic groups. there are also different kinds of ace2 knockout mouse models, with names like balb/c k18-hace2. so, if you run a weaponized pathogen through a lot of generations of mice bearing, say, the ace2 receptors of only westerners, the pathogen will develop a preference for infecting those with enough serial passaging. there's another receptor at play, tmprss2, with the same bias.
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