Might be the difference between effectiveness against the strains they were designed for, and effectiveness against whichever strain ends up being dominant in the year they were administered.
Some years they totally blow it. I worked with a guy who didn’t get it, one year his Doctor was really on his case about it and he replied “you and I both know they’re just guessing at it” and his Doc relented.
I recently heard it on the Dan Bongino show. I trust his analysis but, I will now verify!
Might be the difference between effectiveness against the strains they were designed for, and effectiveness against whichever strain ends up being dominant in the year they were administered.
Some years they totally blow it. I worked with a guy who didn’t get it, one year his Doctor was really on his case about it and he replied “you and I both know they’re just guessing at it” and his Doc relented.