What does that do ?
The vaccine is supposed to be injected into the deltoid muscle tissue and stay at that location. The deltoid muscle has few capillaries in it, so the chances of injecting the vaccine into the bloodstream are small. The theory is that injecting the vaccine, even a small amount, into the bloodstream delivers the vaccine to organs where it doesn’t belong and can cause all sorts of organ and health damage. Japanese data was released about six months showing the vaccine concentrating in certain organs which was unexpected. There is suspicion that the cardiac problems might be caused by intravenous injection of the vaccine.
“Aspiration” simply means that you push the needle in and pull the plunger back a tiny bit. If the needle hit a blood vessel, you will see red in the syringe and know that you don’t want to inject there. You pull the needle out and try a different location. If no red in the syringe, you are in muscle tissue, so go ahead and inject.
That’s my layman’s understanding (which the nurse confirmed).
I learned about this potential problem in one of the many articles on FR.