“Overshooting herd immunity” means we achieve herd immunity in the space of a few weeks, with perhaps 60+% of all Americans getting sick; and then (because the total number of infectious people is so high) a large portion of the rest of the population gets infected too even though the virus’s effective reproduction number R is much lower now.
I don’t understand what that means. How is herd immunity in this context formally defined?
The cumulative proportion of individuals who get infected during the course of a disease outbreak can exceed the HIT. This is because the HIT does not represent the point at which the disease stops spreading, but rather the point at which each infected person infects fewer than one additional person on average. When the HIT is reached, the number of additional infections begins to taper off, but it does not immediately drop to zero. The difference between the cumulative proportion of infected individuals and the theoretical HIT is known as the overshoot
If, at the time we reach the Herd Immunity Threshold, many people are infected, an R number of eg 0.5 will cause a large number of others to be infected.
I don’t understand what that means. How is herd immunity in this context formally defined?
Wikipedia:
If, at the time we reach the Herd Immunity Threshold, many people are infected, an R number of eg 0.5 will cause a large number of others to be infected.