The expectations list is problematic. 2020 waves reversed with seropositivity and experienced illness still ultra-low, 3 - 10% in lockdown countries. In the West only Sweden and Italy were higher https://onlinelibrary.wiley.com/doi/10.1111/vox.13221 - Granted, the dead can't contribute to seropositivity, but deaths were essentially rare vs. population, so the AR among "susceptibles" would be the same as overall AR, with a possible caveat for locales that turned nursing homes into hotspots.
So there's no grounds for asserting that susceptibles have been removed. Presumably only 3 to 10% of them have. There's lots of shoes left to drop.
As such, any gains in fitness / virulence would at best have a .1 discount from prior immunity / removal of susceptibles in most countries. .1 is a rounding error in terms of the possible delta of mutations on fitness / virulence. Given that the "reward" for increased fitness is an additional 9 times as much infection and replication as achieved in the first wave, i.e. the conquest of that remaining 90% of hosts, there's no reason to expect any reduction in deaths in future waves per se. And this just repeats for all additional waves up to Delta, because they keep ending with not much movement on seropositivity.
Only in the Omicron era can you start to include accumulated natural immunity as a serious factor in expected/observed epidemiology/evolution. Hence why it is only recently that there has been a lot of actual immune escape mutations, whereas the 2020 VOCs had one or two escape mutations to their name at most.
For the three age groups truly at risk (65-74, 75-84, 85+), excess mortality in 2020 per https://www.usmortality.com/excess-mortality/yearly-percentage-cumulative appears to be ~16%, 21%, and 26%, respectively. I would think this represents a significant population of folks especially vulnerable to bad outcomes, who would then not be present in future waves. An additional significant portion of these age groups would have been infected and recovered, making them far less likely to have a bad outcome in a future wave.
On average (weekly) the % of COVID deaths in the 65+ group was ~76%, so any significant number of deaths and infections among this group in 2020 should significantly reduce the susceptible population in 2021 and beyond, no? Perhaps I didn't fully understand your objection.
Right, but excess mortality scales to baseline, which is single digits until you get to 85+. 16% of 2% is just 0.3%.
But at the same time the n for people aged 50-84 is much larger than the n for people 85+, so much so that the latter are like tip of the tip of the iceberg - because they are already dying off all the time, sans virus. So you have this huge pool of susceptibles in 50-84 who in early 2020 are only .24 x .01 removed. The virus has basically opened the box and eaten a single cheerio at that point, if you're only talking deaths. Deaths + recovered alive, maybe half a bowl at best, again it varies by lockdown intensity and there's no reason to consider seropositivity a bad measurement.
Also - it may be useful to link to the previous post
intended to. Thanks, post updated with link.
The expectations list is problematic. 2020 waves reversed with seropositivity and experienced illness still ultra-low, 3 - 10% in lockdown countries. In the West only Sweden and Italy were higher https://onlinelibrary.wiley.com/doi/10.1111/vox.13221 - Granted, the dead can't contribute to seropositivity, but deaths were essentially rare vs. population, so the AR among "susceptibles" would be the same as overall AR, with a possible caveat for locales that turned nursing homes into hotspots.
So there's no grounds for asserting that susceptibles have been removed. Presumably only 3 to 10% of them have. There's lots of shoes left to drop.
As such, any gains in fitness / virulence would at best have a .1 discount from prior immunity / removal of susceptibles in most countries. .1 is a rounding error in terms of the possible delta of mutations on fitness / virulence. Given that the "reward" for increased fitness is an additional 9 times as much infection and replication as achieved in the first wave, i.e. the conquest of that remaining 90% of hosts, there's no reason to expect any reduction in deaths in future waves per se. And this just repeats for all additional waves up to Delta, because they keep ending with not much movement on seropositivity.
Only in the Omicron era can you start to include accumulated natural immunity as a serious factor in expected/observed epidemiology/evolution. Hence why it is only recently that there has been a lot of actual immune escape mutations, whereas the 2020 VOCs had one or two escape mutations to their name at most.
For the three age groups truly at risk (65-74, 75-84, 85+), excess mortality in 2020 per https://www.usmortality.com/excess-mortality/yearly-percentage-cumulative appears to be ~16%, 21%, and 26%, respectively. I would think this represents a significant population of folks especially vulnerable to bad outcomes, who would then not be present in future waves. An additional significant portion of these age groups would have been infected and recovered, making them far less likely to have a bad outcome in a future wave.
On average (weekly) the % of COVID deaths in the 65+ group was ~76%, so any significant number of deaths and infections among this group in 2020 should significantly reduce the susceptible population in 2021 and beyond, no? Perhaps I didn't fully understand your objection.
Right, but excess mortality scales to baseline, which is single digits until you get to 85+. 16% of 2% is just 0.3%.
But at the same time the n for people aged 50-84 is much larger than the n for people 85+, so much so that the latter are like tip of the tip of the iceberg - because they are already dying off all the time, sans virus. So you have this huge pool of susceptibles in 50-84 who in early 2020 are only .24 x .01 removed. The virus has basically opened the box and eaten a single cheerio at that point, if you're only talking deaths. Deaths + recovered alive, maybe half a bowl at best, again it varies by lockdown intensity and there's no reason to consider seropositivity a bad measurement.