I understand the thinking is that the efficacy is 91% after the second dose has been given but before that second dose would have had any effect, i.e. it would have got to 91% regardless.
Seems like a good idea to me.
No mention of this in the medical journals. 52% after first, 95% 7 days after the second.
https://www.bmj.com/content/371/bmj.m4826#:~:text=Read%20our%20latest%20coverage%20of%20the%20coronavirus%20outbreak&text=The%20study%2C%20published%20in%20the,cases%20in%20the%20placebo%20group.