Are you referring to aspiration vs intravenous injection? I am not a medical doctor, but John Campbell and his presentation of data from Denmark convinced me to ask for aspirated admission of my dose(s). Can't find the presentation rn, unfortunately, but some similar considerations are mentioned here [1]
Oh, I saw a video in 2021 in which a retired doctor/uni. prof. explained AZ complications (it was someone from the UK) were most likely/could be related to how nurses handled the needle and where they stung it. Like, he was concerned about the lack of instructions given to vaccinating squad. I blacked this info out because it was too much of a yet another thing I had to watch for at the time on top of others but for my first booster I had a chat with the nurse about the dosage of the booster and... yeah... better check these kind of things out yourselves, things can go wrong really fast (and mark your legs and operation instructions on your body before going under the scalpel :).
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.
[1] https://pubmed.ncbi.nlm.nih.gov/35320581/