Absolutely it would need to be looked at, but the fact that there were large numbers of both means you should be able to factor that out, as far as easy demogra

Absolutely it would need to be looked at, but the fact that there were large numbers of both means you should be able to factor that out, as far as easy demographic variables like age and sex. However, and this is to your point, if (in any given country) one of those became available well before the other, then those people who were more eager to get it would all get one type, and people with pre-existing conditions might be expected to mostly be in that group.