Recently I read someone arguing against pharmaceuticals saying COVID 19 vaccine immunity would last around a year. His argument was that how do they know that it's good for a year if a year has not passed yet.
I answered that maybe it had to do with the fact that diseases mutate and they just measure the rate of mutation of the disease to be able to predict the lasting effect of the vaccine, but I'm not really sure about that, I'm not a medic.
How does it work? and is there a formula for this? Thanks!