The vaccines work, in part, by preventing binding between the virus and the host cell receptor. It also produces antibodies that can be distinguished from those created during natural infection.
The Pfizer vaccine is a little faster than the Oxford vaccine in creating antibodies; however, both of these vaccines show about the same efficacy at four weeks.
Some people may see less efficacy of the vaccines, particularly those who have undergone organ transplants.
Read more on this topic at https://www.news-medical.net/news/20210519/Spike-antibodies-after-vaccination-with-Pfizer-and-Oxford-vaccines.aspx