Pasta :
Have you read how every stage of the development of this vaccine has been expedited? Have you read the reasons why other vaccines took so long?
Oxford didn't begin developing in March. They were already planning and working on a Coronavirus vaccine. It just needed tweaking and of course funding. Money suddenly became no object and the path through testing and licensing has also been smoother than in years gone by when urgency wasn't a factor.
We read an interesting article the other day because we were asking much the same question as you. We have a personal interest in the Oxford vaccine team and follow it closely in news and otherwise.
https://www.bbc.com/news/health-55041371
A long but fascinating article.