It seems like there is new evidence of significant risk of blood clots associated with the AstraZenica vaccine for young women.

• NPR story

That story references but does not cite these studies from the New England Journal of Medicine:

• Thrombotic Thrombocytopenia after ChAdOx1 nCov-19 Vaccination
• Thrombosis and Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination

So it seems like there is significant risk associated with the AstraZenica vaccine for certain age groups, and that it may make sense to avoid for those people.