very old dr told me he noticed the techs who gave him his shots failed to follow the best practice he was taught, which is to withdraw the plunger to see if you pull out any blood. If you draw any blood you have hit an artery and need to start over.
His vax people just stuck it in and plunged, no testing.
I’m not in this field at all, but having read a lot of research papers at the time it is my understanding that many countries have revised this recommendation (some even before Covid). It takes additional time, causes significant additional discomfort to patients, requires more training of whoever is administering the vaccines, and does not provide significant benefit. Similarly, it’s no longer commonplace to wipe the arm with alcohol before an injection, yet that was always considered best practice in the not-too-distant past.
His vax people just stuck it in and plunged, no testing.