I interpret this as some good news. If having Covid-19 provides lasting immunity (years?) then I think that would mean the 5 million or so Americans who have had it and recovered and go back to normal life. Am I missing something?
Yes, there is a lot still missing. We don't know if everybody who gets the disease has immunity, and we have no idea how long such immunity would last. Until those things are figured out, giving out "immunity passports," as it were, to resume normal activities, is a mistake.
They are finding that prior exposure to other coronavirus infections (common cold, animal viruses) leaves behind t-cells that are activates for covid-19, as long as 17 years. And that a large percentage of the population has these t-cells. [0]
Perhaps that explains why we have appeared to reached herd immunity in places like northern Italy, NYC, etc. The tests for b-cell antibodies don't detect t-cells.
Worst case predictions are just not panning out for this virus. It is like other coronavirus infections. It was expected to decrease in severity and become endemic, perhaps another common cold variant of something that comes up like a bad flu year every once in a while [1]
~5M is the number of people who tested positive by PCR. That's a small share of the total infected, though, since most people don't get sick enough to seek medical attention.
The total is probably around 25M Americans infected, 174k dead divided by 0.7% IFR[1]. That IFR was calculated from prevalence of IgG antibodies in random samples of the population. The antibody test thresholds were established using blood from patients who tested positive by PCR. Those patients generally wouldn't have sought care if the symptoms were very mild, and milder illness is associated with lower levels of antibodies in the blood. So that estimate of the IFR is probably conservative (i.e., high if anything, so the estimate of the total infected is low if anything). Different populations will see different IFRs, especially with variation in the age distribution (since the IFR is >100x for old vs. young), and also to a lesser extent with other factors.
Immunity passports have been endlessly discussed, and have many problems (e.g., the incentive for people to deliberately get infected) that I suspect will prevent wide adoption. It would make sense e.g. to preferentially assign seropositive medical staff to work with vulnerable patients, though.
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[ 2.6 ms ] story [ 5.9 ms ] threadPerhaps that explains why we have appeared to reached herd immunity in places like northern Italy, NYC, etc. The tests for b-cell antibodies don't detect t-cells.
Worst case predictions are just not panning out for this virus. It is like other coronavirus infections. It was expected to decrease in severity and become endemic, perhaps another common cold variant of something that comes up like a bad flu year every once in a while [1]
[0] https://www.nature.com/articles/s41586-020-2598-9
[1] https://www.statnews.com/2020/02/04/two-scenarios-if-new-cor...
The total is probably around 25M Americans infected, 174k dead divided by 0.7% IFR[1]. That IFR was calculated from prevalence of IgG antibodies in random samples of the population. The antibody test thresholds were established using blood from patients who tested positive by PCR. Those patients generally wouldn't have sought care if the symptoms were very mild, and milder illness is associated with lower levels of antibodies in the blood. So that estimate of the IFR is probably conservative (i.e., high if anything, so the estimate of the total infected is low if anything). Different populations will see different IFRs, especially with variation in the age distribution (since the IFR is >100x for old vs. young), and also to a lesser extent with other factors.
Immunity passports have been endlessly discussed, and have many problems (e.g., the incentive for people to deliberately get infected) that I suspect will prevent wide adoption. It would make sense e.g. to preferentially assign seropositive medical staff to work with vulnerable patients, though.
1. https://www.medrxiv.org/content/10.1101/2020.05.03.20089854v...