Testing has been capturing only from 10% to 25% of infections, depending on when during the pandemic someone got the virus. Applying a time-weighted case capture average of 1 in 6.5 to the cumulative 28 million confirmed cases would mean about 55% of Americans have natural immunity.
Unfortunately, he does not spell out his calculations enough for me to check. But it is likely that he is badly mistaken. Yes, back in March and April, we were not doing very many tests, and a large share of infections went undetected. I doubt that this has been true in recent weeks. I bet that the number of undetected cases in the last two months is less than double the total number of detected cases over that period. If so, then his claim that we will have herd immunity by April is probably unsound.
Number One Pick, who I think is a more credible observer, wrote,
Prediction: 75% chance that there will be a new wave peaking in March or April, with a peak at least half again as high as the preceding trough.
[EDIT: some people link new studies saying the B117 strain is less virulent than previously believed, and the US has been getting much better at vaccination since I checked, probably my prediction above is too high and we should worry less about this]
So it is hard to say what his current prediction is. I am guessing that he would put a low probability on herd immunity by April.
UPDATE: The 7-day average death rate has really plummeted over the past week. So maybe I should be more optimistic.
David Friedman also asked Have We Reached Herd Immunity? last Sunday.
“But it is likely that he is badly mistaken.”
“Number One Pick, who I think is a more credible observer”
John Hopkins medical doctor vs. a psychiatrist from University College Cork School of Medicine in Ireland who has a mediocre batting average so far on the virus.
Ok – call me a sucker, but I’ll go ahead and bet against Dr. Siskind. Please propose your terms and then you can take my $100 come April. I’ll send it to you via Zelle.
“His forecasts suggest that about 61% of the population should have some form of immunity—either from the vaccine or past infection—by June.”
https://www.bloomberg.com/news/articles/2021-02-19/covid-pandemic-how-youyang-gu-used-ai-and-data-to-make-most-accurate-prediction
Andrew Atkeson (UCLA & NBER) has produced a fresh model that captures the course of pandemic transmission and death rates in the USA and UK before vaccination. Key parameters are (a) behavioral adaptation to changes in death rates and (b) pandemic fatigue. Atkeson predicts that the timing of herd immunity will depend on the pace of vaccination of people who haven’t already acquired natural immunity through infection and recovery. Makary (WSJ) includes a vaccination parameter in his prediction that herd immunity will arrive quickly. Atkeson models what would happen if vaccination doesn’t proceed apace — and it’s not pretty.
See link, abstract, and excerpts below.
https://www.nber.org/system/files/working_papers/w28434/w28434.pdf
“ABSTRACT
I present a behavioral epidemiological model of the evolution of the COVID epidemic in the United States and the United Kingdom over the past 12 months. The model includes the introduction of a new, more contagious variant in the UK in early fall and the US in mid December. The model is behavioral in that activity, and thus transmission, responds endogenously to the daily death rate. I show that with only seasonal variation in the transmission rate and pandemic fatigue modeled as a one time reduction in the semi-elasticity of the transmission rate to the daily death rate late in the year, the model can reproduce the evolution of daily and cumulative COVID deaths in the both countries from Feb 15, 2020 to the present remarkably well. I find that most of the end-of-year surge in deaths in both the US and the UK was generated by pandemic fatigue and not the new variant of the virus. I then generate forecasts for the evolution of the epidemic over the next two years with continuing seasonality, pandemic fatigue, and spread of the new variant.”
Excerpts:
“I find that seasonality is key in accounting for the relatively low level of daily deaths observed during the summer of 2020 in both countries, and in both countries, the model with a fixed behavioral response and seasonality alone does a remarkable job in matching the pattern of daily deaths through the late summer of 2020. I find that pandemic fatigue is key in accounting for the onset of a large second wave of deaths experienced this Fall and Winter in both countries. In particular, seasonality in transmission is not sufficient to generate a large second wave of deaths because behavior endogenously offsets a gradual rise in the inherent transmission rate of the virus. For the United Kingdom, I find that the specification of the model with seasonality and a new variant but without pandemic fatigue also does not generate the large wave of deaths experienced in that country late in the year. Thus, I conclude that most of that wave was accounted for by pandemic fatigue and not the new variant.
One concern about the results regarding pandemic fatigue found here is that no dramatic change in cell phone mobility data can be seen in those data in the window of time for which my assumed pandemic fatigue shock occurs. This discrepancy between model and data may reflect either a problem with the model or a problem with the cell phone mobility data as an indicator of the impact of human behavior on virus transmission. It is intriguing that the model assumed onset of pandemic fatigue in the United States coincides with the announcement of success of the Phase 3 trials of the Pfizer vaccine in the United States on November 9 and shortly after the announcement of the success of the Phase 3 trials of the Oxford-AstraZeneca vaccine in the United Kingdom on November 23. Perhaps the news of vaccines led to subtle changes in individual behavior that reduced the endogenous responsiveness of the transmission rate to daily deaths.
I find that without a successful vaccine program, a substantial third wave of deaths is likely in both countries in the Fall and Winter of 2021 and cumulative deaths would asymptote to a level just shy of 1.25 million in the US with 75% percent of the population experiencing the virus by late summer 2022. The analogous forecasts for the United Kingdom are just over 240,000 cumulative deaths and just over 70% of the population experiencing the virus by late summer 2022. These results indicate that a successfully executed vaccination program could potentially save a large number of lives in both countries, roughly half a million in the United States and one hundred thousand or more in the United Kingdom.”
Atkeson seems to use an implied mortality rate (IFR) of 0.50% (*), yet he doesn’t quote any source for it or explain why it contradicts what has been published so far (**).
(*) (1250/ 330000) / 0.75 = 0.50%; (240 / 67900) / 0.7 = 0.50%
(**) https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=gangelt+covid
If we judge the end by total cases, April may be optimistic. If as judge it by deaths and hospitalizations – the metrics that matter – April seems right. Enough of those most susceptible to severe infection and thus prone to hospitalization / death will have been vaccinated by then.
Israel should be much further ahead of us on the the herd-immunity track, but oddly, their numbers don’t yet seem to declining very much faster.
I’m willing to bet we’ll see a big divergence open up in two weeks, and in a month, they’ll be over the pandemic, and we won’t be.
That is, claims of our herd immunity will once again turn out to be premature as personal behavior and policies loosen up with good news, and we get the “tennis chair umpire” experience again. The way I think about it is the “reserve army of the uninfected and not-vaccinated.” We know most people have not been vaccinated, and you really have to believe that truly huge numbers of people caught it but never knew.
So, again, my bet is that Israel just got to herd immunity, and being way ahead of us, it means we’re not that close. But so far, it’s not obvious just from the numbers. If anything, to the extent coincidental timing of seasonality is a confounding factor, Israel should be even more ahead of us, since it’s already spring-like in the Levant.
My read of things is that Israel reached herd immunity just recently, which doesn’t mean the trouble is ‘over’, only that infections can’t spread exponentially any more and must continue to decline quickly from this point on. Total number of known infected people there just peaked, and the rates of new cases and deaths per day are down 50% from just a few weeks ago. Practically every elderly person in the country who is not a stiff-necked holdout has now had their second shot, and most adults have had one shot. The target level of five million adults will have have their first shot by March 1, and everybody will have their second shot by April 1.
I feel about all this like visiting Soviet officials felt when walking into American supermarkets.
Having to already deal with holdouts because you’ve worked through all the people in line and *even healthy teenagers* is very much a ‘first world problem’ (think about that for a minute), and Netanyahu has already been working them by (1) making one feel like one will be left out of the celebrations, stuck alone in one’s apartment while everyone else is posting messages on social media of what a great time they’re having while one has got nothing to post back – that’s real psychological pressure these days – and (2) Free good food at the jab sites. The guy is a genius and knows what he’s doing.
I can remember first seeing Netanyahu on TV during the Gulf War 30 years ago and saying, “Who’s that? I think we are going to be hearing more from this guy.”
I bet that the number of undetected cases in the last two months is less than double the total number of detected cases over that period.
I’m agnostic — yes, we do a lot more testing but not much of people with minimal or no symptoms.
Prediction: 75% chance that there will be a new wave peaking in March or April, with a peak at least half again as high as the preceding trough.
What would be the behavioral source of an April spike? With weather improving, people will feel less of a need to gather with others indoors, and Easter is nowhere near as big an extended family holiday as Thanksgiving or Christmas. Actually, this prediction seems almost already falsified (if we’re going to have a spike with a March-April peak, it had better get started really soon).
I think you are right on testing. I know at least 4 people that caught it and experienced nothing more than a few days heavy fatigue. Only one tested quickly. I suspect many of the under 65 crowd, or the 90% of cars without serious symptoms just don’t get tested anymore than one gets tested for flu. Or got tested, in the old days.
People who have mild or asymptomatic infections will greatly inflate the number of uncaught cases.
Is herd immunity relevant? The relevant factor should be deaths due to covid. Of course we don’t have any reliable data on that, but nevertheless, despite the genocidal diversity-inclusion-equity hate campaign to prevent whites most at risk from being vaccinated, many are getting vaccinated nonetheless.
Some sources claim 35 percent of covid deaths so far have been residents of long term care facilities. Others state that about 1 percent of the USA population, or 329,000 are residents of such facilities. According to the CDC web site, 998,000 long term care facility residents have been fully vaccinated. At this pace the remaining residents should get vaccinated by the end of may. Some states have begun allowing high risk people with other health conditions and the elderly to get vaccinated as well. As soon as the teachers and other Democratic Party loyalists all get vaccinated more people at higher risk of death from covid might begin to be vaccinated in significant numbers. The threat to this happening though is the one-shotters who would reduce the effectiveness of the vaccines from mid-nineties down to mid-eighties and thus further prolong the carnage in the high death risk groups. Nevertheless, the high risk of death groups may eventually be protected. We may actually begin to see deaths below a hundred a day nationwide and death-free days and weeks in some states and counties in July. At which point, what difference would herd immunity make?
Deaths have been artificially inflated the previous week by Ohio’s reassignment of about 4000 deaths from months ago. The last of those tallie fell out of the 7 day average yesterday, and accounts from almost 600 deaths/day drop in the national total.
As for subsequent waves- well that depends on whether or not we continue to test everyone who requests a test free of charge, and also whether or not we start including tests for mutant variants of COVID. If the false positive rate is 1-2% depending on the competence of the lab, then at 1.5 million tests/day, you can get between 15,000 and 30,000 new “cases”/day as the noise baseline, and of those 15,000-30,000/day 1% of them will die within a year- or 150-300/day using the death certificate matching now being utilized by pretty much every single state in the US.
In short, the pandemic ends when the testing for the disease ends. Who is going to make that decision?
John Cook spelled out his calculations that led to a “late April” herd immunity conclusion:
https://www.johndcook.com/blog/2021/02/19/herd-immunity-countdown/
Of course, now that we have the testing infrastructure built out for 2-3 million PCR tests/day along with the sample collection infrastructure, we can now identify pandemics with the various influenza strains every Winter. We can have school shutdowns, house lockdowns, and mask mandates pretty much at will.
“We can have school shutdowns, house lockdowns, and mask mandates pretty much at will.”
Frigging awesome – something for the blue states to look forward to! Follow your “science” blue states! Meanwhile, us backwards deplorables in the red states will proceed with a different approach.
It has always been likely that only about 2/3 to 1/2 the population was even infectable with COVID-19 to the extent they would even notice the infection. If you were vulnerable to every novel strain of respiratory virus, you would be sick all the time if you are sociable to any great extent.
There is going to be divergence between cases and deaths. Once the 16% of Americans over 65 are vaccinated we’ll be over the hump with Deaths. However Cases may rise as new strains become dominate, and people start changing their behavior because of the low death/hospitalization rates. By end of April we’ll start to see life back to normal, but not because of herd immunity. We’ll not reach that for a while, but over 50% will be immune, and Rt will drop below 1 and stay there,
So, I have a heterodox opinion that the proportion of undetected Spring 2020 cases is much smaller than we think–and indeed than I thought until recently.
Here’s my evidence:
In Massachusetts, the water department has been performing sewage testing since the start of the pandemic. The Deer Island Treatment Plant collects sewage for over 2 million people across metropolitan Boston, so it’s a big sample and because everybody uses the bathroom, this testing modality should not be subject to all the usual gotchas around test availability, compliance, etc. Throughout the past year, the shape of the wastewater curve has followed the trend in confirmed cases extremely well.
See: https://www.mwra.com/biobot/biobotdata.htm
I did a very simplistic and naive area-under-curve approximation for the two “waves” here, from 3/1/20-5/31/20 and 11/1/20-1/31/21, and then divided this by the number of new cases confirmed during the same period.
Spring Wave: 0.66 AUC / case
Winter Wave: 0.97 AUC / case
From a testing volume perspective, the number of tests run in the winter is roughly 10 times as many as in the spring. By October the *daily* test rate reached roughly 1% of the population which is among the highest anywhere.
If you assumed that our current testing regime catches “most” cases, and that our spring testing regime caught maybe one-fifth as many, then you would expect the numbers to be like 4 or 5 for the spring to the 1 they were in the winter. And in fact the two are nearly the same, which suggests that our testing didn’t underestimate the prevalence anywhere near as much as we think.
Thank you for this, that is a great resource. The drop in the last month is incredible and can’t just be vaccines or herd immunity.
If I had to guess, I think compliance with the lockdowns is finally be effectively enforced, not by Uncle Sam, but by Mother Nature. And that rough late winter is keeping people in their homes to such an extent that it is overcoming even the typical seasonality. We’ll see.
“Yes, back in March and April, we were not doing very many tests, and a large share of infections went undetected. ”
Have you looked at daily testing? Yes, higher than April but testing rate has been on a nose dive since around Jan 25th.
https://ourworldindata.org/grapher/daily-tests-per-thousand-people-smoothed-7-day?tab=chart&stackMode=absolute&time=earliest..latest&country=~USA®ion=World
The CDC estimates 83 million people were infected from Feb -Dec 2020. You can scratch off another 40 million for age under 9 because most of them are effectively immune. Add in the number infected so far this year and we are in the vicinity of 50% total immune.
How much overlap is there between those who were already infected and those who have vaccinated?
A clinical lab scientist tests 1,500 positive Covid-19 samples and finds nothing but common influenza viruses.
https://gab.com/Ruth-Plant/posts/105730290598245938
That modeler the twitterverse loves so much, because of his uncanny accuracy, Youyang Gu (subject of a recent Bloomberg article, he’s breaking out of twitter), thinks about 75% chance there will be no 4th wave…due to seasonability and vaccinations….. Also, he thinks herd immunity is next year, but return to normal this summer…