It’s not surprising that historically plague-ridden Europeans would be less susceptible to a new blight then other ethnicities. Disease resistance has been selected for.
Cystic fibrosis is a predominantly Caucasian genetic disorder because one copy of the gene helps protect against certain historical plagues in Europe without being too debilitating. But two copies kill you gruesomely at a young age. And it kills you primarily by making you more prone to infection.
Kind of like how Sickle Cell works. It helps protect against malaria, but two copies of the gene are bad news.
In western countries at least, an obvious confounded for those of asian or black ethnic descent is _poverty_ and thus access to healthcare, malnutrition, sleep deprivation, poor education and everything else that goes with poverty.
The two regions often responded very dissimilarly. nKyle Harper'sbThe Fate of Rome looks at this in depth.
TL:DR; civilisation's patterns (cities, trade, travel) co-evolve diseases. Populations tend to evolve resistance to local endemic disease, but are susceptible to novel agents, including foreign infections. Rome infected China and vice versa.
