Comment by UncleOxidant

John Campbell suggested on his video the other day that perhaps this is happening because some injectors are not aspirating. What that means is that when an intramuscular injection is given you want to ensure that it goes into the muscle and not into a vein. So the proper way to do this is for the person doing the injection to first pull out the syringe (after it's been stuck into the arm) a bit to make sure there's no blood coming out. Then if not, the vaccine is pushed in. If blood is seen then a new site has to be chosen. Apparently Denmark has included aspiration in their directions for usage of the AZ vaccine.