I am a little rusty on my probability basics now but I was trying to remember how one would go about answering the following question regarding Wuhan numbers cited in this study:

"Given a person has type A blood type, what is the probability of that person having covid19"

I remember this being something like P(E1 intersection E2)/P(E2) where E2 = event that a person has type A blood and E1 = event that the person has covid19.

In case of Wuhan 32.16% of the population has type A blood. So E2=0.3216. To get E1 we would need total infections/total population for the city. We don't have that number but is this thinking correct?