That may be but they must have some indication of how strong a response those who got the vaccine are generating vs the time they entered the trial. Is there fall off? More or less than expected? How confident are they that immunity will last at least a year?
They don't really have an indication of that. The way these trials work is just that they send everyone out to live their lives and check infection rates in the experimental group against the control group, so there's no effective way to dig in deeper to the biomechanics of it. A standardized measurement of immune response could only be done through what's known as a "challenge trial", where participants are deliberately infected with a predetermined dose; some of these are in the works, but none have yet been approved or performed.
