A nurse friend of mine raised this as a concern. The protocol for intramuscular injections used to be (and in some places still is) to draw the plunger back a b

A nurse friend of mine raised this as a concern. The protocol for intramuscular injections used to be (and in some places still is) to draw the plunger back a bit first to verify that you're in muscle, and haven't hit a small vein. If you pull blood, you find new spot. In practice this doesn't happen for covid vaccines, and her personal hypothesis was that many of the adverse reactions (myocarditis, or just being hit hard) were due to the vaccine partially being administered into a vein.