I wonder if because the Oxford vaccine has taken an already tested and approved vaccine approach it has a higher chance of safety than the other 2 which use a new approach that has never been approved by regulators before.
FTA: "The Oxford vaccine (ChAdOx1 nCoV-19) is made from a virus, which is a weakened version of a common cold virus (adenovirus), that has been genetically changed so that it is impossible for it to grow in humans. Adenovirus vaccines have been researched and used extensively for decades"
