The other 'random' variable is that the vax overlords know each nurse (and every arm they jab) is a different situation. If the juice doesn't land in the muscle and hits the blood stream, all bets are off. I believe this is the most important random part of the setup. It is situational, but bound to happen. This is why the deaths are so random, and while prevalent, are not easily attributable to a certain ethnicity or other biological characteristic.