you assume states with more restrictions had the same vulnerability as others ( :
but yes, we are more population-dense in some regions and less so in others, as some countries are more or less than us, as every country has at least a slightly different culture. i don't see how to reasonably account for those and other variables. some countries under more authoritarian regimes did better for that reason, i suppose.
is China developing race-specific germ warfare? are we? if so, it's unlikely that we'd know of it.