I think different people have used it to mean different things, which is an easy way for concepts to shapeshift.
The percentage of the population infected at the ‘herd immunity’ stage is dependent on R0, the transmission rate; each newly infected person has to, on average, hit less than one not-yet-immune person. And so if 80% of the population has already had it, you can afford to roll against up to 5 individuals; if 50% of the population has already had it, you can afford to roll against up to 2 individuals. Then the number of new infections is a shrinking number, and eventually you get no new infections (while some fraction of the population never got the disease).
I think early on people were mostly worried about access to ventilators; it’s ‘fine’ if people get the disease, so long as sufficiently few of them get it at any particular time. Drop the R0 to 1, and a manageable infection stays manageable (and an unmanageable one stays unmanageable).
I think most internet commentators were overly optimistic about how effective minor adjustments would be, and empirically it’s taken the ‘social distancing’ / ‘shelter in place’ / ‘lockdown’ state that most of the world is currently in to get the R0 below 1, rather than just people being more diligent about washing their hands.
There are only a few ways out of this mess, and they all involve the number of active cases going (functionally) to 0. Suppression (whatever measures it takes to get R0 sufficiently close to 0, instead of 1), herd immunity (enough people getting it and recovering that future social interactions don’t cause explosions), or a vaccine (which gets you herd immunity, hopefully with lower costs).
I think different people have used it to mean different things, which is an easy way for concepts to shapeshift.
The percentage of the population infected at the ‘herd immunity’ stage is dependent on R0, the transmission rate; each newly infected person has to, on average, hit less than one not-yet-immune person. And so if 80% of the population has already had it, you can afford to roll against up to 5 individuals; if 50% of the population has already had it, you can afford to roll against up to 2 individuals. Then the number of new infections is a shrinking number, and eventually you get no new infections (while some fraction of the population never got the disease).
I think early on people were mostly worried about access to ventilators; it’s ‘fine’ if people get the disease, so long as sufficiently few of them get it at any particular time. Drop the R0 to 1, and a manageable infection stays manageable (and an unmanageable one stays unmanageable).
I think most internet commentators were overly optimistic about how effective minor adjustments would be, and empirically it’s taken the ‘social distancing’ / ‘shelter in place’ / ‘lockdown’ state that most of the world is currently in to get the R0 below 1, rather than just people being more diligent about washing their hands.
There are only a few ways out of this mess, and they all involve the number of active cases going (functionally) to 0. Suppression (whatever measures it takes to get R0 sufficiently close to 0, instead of 1), herd immunity (enough people getting it and recovering that future social interactions don’t cause explosions), or a vaccine (which gets you herd immunity, hopefully with lower costs).