The adenovirus vaccines were found to slightly increase the risk of blood clots. The mRNA vaccines do not increase blood clot risk. Covid-19, of course, greatly increases the risk of blood clots, which occur in about 30% of hospitalized Covid patients.
Partly because of the slightly increased risk of blood clots with the J&J vaccine, the FDA revoked approval of this vaccine in June, 2023. It is not surprising, therefore, that the AstraZeneca vaccine is also being pulled.
I do not know if other vaccines based on an adenovirus vector would also increase the risk of blood clots. I also do not know why the adenovirus-based vaccines had this risk. There is currently a gene therapy being developed which uses adenovirus to deliver a gene encoding VEGF (vascular endothelial growth factor) to help patients with angina grow new blood vessels in the heart and decrease the angina pain. Although this use of the adenovirus is called a gene therapy (because it replicates what a natural human gene does), it is doubtful that the adenovirus will stick around for any length of time.
Gene Therapy Allowing Heart to Grow New Blood Vessels Supported by Early Data