There are a lot of stats re efficacy flying around for the AZ vaccine. Lets go thru them:
-70.4% is a pooled estimate from the low dose & standard dose groups,Dec 8, n=11,636. Criticised for combining 2 distinct groups different wrt age, dosing interval & vaccine dose 1/n

62.1% from Dec 8 is the group who got 2 standard doses, (n=8,895); confirmed in a pre print Feb 1: 63.1% in n=14,379 pts (1 month more of data).
-dosing interval was highly variable: 54% got 2nd dose less than 6 wks, 18% 12 wks or more, with others in between

76% comes from a post hoc analysis (a subset of main trial data) of a single shot preventing symptomatic (not asymptomatic) infection from d22 to d90 , w wide uncertainty (95%CI 59-86%)...3/n

82.4% is the efficacy after extending the dosing to 12 wks or more in a post hoc analysis from n=2,649 w uncertainty in this estimate ranging from 62% to 92%. 4/n

Why does one shot have a higher efficacy (76%) than 2 standard doses (62-63%)? Why does spacing the dosing interval to 3 months or more appear to be better (but in a small cohort? Post hoc analyses are best at asking questions than answering them. For that you need a trial. 5/n

Hence, I take post hoc analyses w a grain of salt bc they are prone to bias, there is greater uncertainty around estimates (bc numbers are smaller) & you may find patterns where there are none. Do the randomised trial to answer the question thrown up by the post hoc. End