- Camino(s) past & future
- 100 characters or fewer : see signature details
I did not say anything about the latter "defining" herd immunity, I said that the present trend of a downward shift of the average age of people being infected might be evidence (i.e. not "proof" nor "demonstration") of a shift towards that herd immunity. My attempt to explain why and how it might be such evidence clearly should not be interpreted as what herd immunity in itself constitutes.I think there is some confusion here. The concept of herd immunity is quite straightforward. Here is a definition:
“a situation in which a sufficient proportion of a population is immune to an infectious disease (through vaccination and/or prior illness) to make its spread from person to person unlikely.”
There is no reference to "the most vulnerable" nor to any shift "away from the most vulnerable". The sine qua non is the sheer number of immune persons in the population whether achieved through an episode of the illness or through vaccination.
As to your final point, and more particularly as to the Covid19, it's "whether achieved through an episode of the illness or through vaccination" ... "or through t-cell cross-protection from previous infections by other coronaviruses".
(hmmmmm, maybe these posts should have been in the old "maths and Covid19" thread ?)