It may just be that it worked on 2 out of 3 people, regardless of race. The female originally didn’t respond to the first dose and required a second dose, unlike the white male - so that’s an indication of how individuals respond differently. We don’t know the way the African doctor’s prior health history compared with that of the whites. I see your point, you may be right, but I wonder if the African’s health was not as good to start with.
That could be true about the two out of three and perhaps the African in not as good health.
There is an article on ABC news, which I am not sure that it is allowed to post the link, that researchers have found that the Black Death may have been an Ebola virus and not a Bubonic plague. They state that the plague did not spread like a disease spread by fleas or rats but spread person to person like Ebola.
That would lend credence to the theory that those who survived the plague are more likely to survive Ebola.
Since it took two doses for the woman versus one for the man, it would be interesting to know whether more males survived the plague than did females.