It's the only solid metric they can report on quantitatively. What else could they report on? There's no way to measure T/B-cell immunity. Plus you can underst

It's the only solid metric they can report on quantitatively. What else could they report on? There's no way to measure T/B-cell immunity. Plus you can understand that if 2 shots give a low immunity level of like 30%, the increase is substantial which would put 3 shots easily above 50% which is solid.