Blood clot risk is much higher the younger you are[1]. It would have been far better to continue using AstraZeneca, but limit it to a certain age and older.
[1] For example, 1.1 of the specific clots per 100 000 vaccinations of people in their 20s, falling to 0.2 per 100 000 in their 60s. https://wintoncentre.maths.cam.ac.uk/news/communicating-pote...