Being exposed every 4 months is not quite herd immunity. Herd immunity is essentially: because some 95% of people are immune to smallpox, if there is an outbrea

Being exposed every 4 months is not quite herd immunity. Herd immunity is essentially: because some 95% of people are immune to smallpox, if there is an outbreak, it will not find any new hosts and would die out. That is very different from "get a booster (or re-infected) every X months to keep immune levels high". In other words, the rapid decay of individual immunity causes for there to be a loss in herd immunity (or herd immunity never achieved at all due to decay in immunity). From a contra-positive point of view, if there were herd immunity, then you would not be able to get re-infected every 4 months because there would be no carriers of the virus to infect you. I think the bottom line is that 'herd immunity' is only a concept if immunity is durable and long lasting. Otherwise that herd immunity decays too quickly and you wind up in a cycle where everyone gets infected, the infection levels drops off, that immunity wears off, rinse-wash repeat. Anecdotally, I was on a train recently and was talking to my neighbors where an elderly woman said casually that the 3rd time being infected she was in the hospital for only 7 days that time. The implication being that this part of the population could land in the hospital repeatedly every 4-6 months. I would wager that someone who is 65 to around 70 years old will survive covid related pneumonia only so many times before they don't. I think this speaks to how Covid is pretty vicious. And all that is to say that 'natural' herd immunity is not our ticket out of this problem (just based on the math). There may be no good tickets out of this short of everyone vaccinating every 6 months and also reducing transmission rates (eg: early detection and quarantining/masking to avoid infecting others, and reducing your own risk of infection via distancing/masking).