Vaxzevria and (I think) most of the other vaccines require intramuscular injection. Which means, don't do an intravenous injection (into the blood).
Researchers, who've been investigating the low level of blood clotting with Vaxzevria, are coming to an understanding of the cause of it.
They're attributing clotting to the vaccine leaking into the blood stream from capillary damage caused by the vaccine injection.
But, as nurse educator John Campbell points out here [mp4], without aspiration, it's possible to give an intravenous injection, and thus increase the chances of blood clotting.
There are recorded deaths from Vaxzevria clotting. They may have been prevented by aspirating the injection site.
But, who can know, when they don't know how many injections were intramuscular, and how many were intravenous?
This is our government's nonsensical contribution. It's from the Australian Immunisation Handbook.
"It is not necessary to draw back on the syringe plunger before injecting a vaccine. However, if you have done this and a flash of blood appears in the needle hub, withdraw the needle and select a new site for injection".