Blood type may be a factor but there isn’t enough data”
Unlike the western world where it’s very rare, China, India and especially Pakistan have relatively high blood numbers of people with type B.
https://www2.palomar.edu/anthro/vary/vary_3.htm
True, it looks that way - but I’m saying there are other variables:
India and Pakistan (ethnically they are one people) - have a hotter climate and more humidity than much of China.
China implemented draconian rules to keep people in place.
I’m not discounting the theory - just saying we don’t have enough data to state it conclusively.
Perhaps if we see the numbers out of India and Pakistan by blood type, we can be clearer.