Frog,I'm no expert on this who is ?
But if huge numbers of people are given a drug, any drug,a very small number will have an adverse reaction,or worse may die.
This goes for cancer drugs,opoiods, diabetes meds,even paracetamol.
You've got to offset this with the huge amount of good they do,if this wasn't the case then these drugs would never get licensed, now the vaccines were put into production far quicker than any other drug but given the situation the world was in,it had to be that way, otherwise imagine how deaths there would have been.