Posted on 05/14/2020 5:29:07 AM PDT by GLH3IL
Conclusion: as the epidemic whirls on, the effective HIT drops dynamically, down-- at the end-- to only 10%.
And-- for everyone worried about whether or not effective first wave suppression has just left everyone vulnerable, and implies a nearly-as-big second wave once distancing is reduced: the model nicely predicts that removing the "highly susceptibles" from the population in the first wave makes the second wave likely rather muted.
(Excerpt) Read more at facebook.com ...
I FEEL HERD
Herd immunity is the magic percentage of the population which needs to be immune (brick wall, baby) before transmission entirely grinds to a halt. Very, very important: whatever the threshold number is, as you approach it, transmission is slower and slower and harder and harder and R0 drops and drops. It's more like molasses freezing, versus switch-flipping.
It's different for every pathogen, and can be calculated quick n'dirty style (the way modelers seldom like it) as follows:
Herd immunity = 1 - 1/R0
So, if your disease makes four new cases for each infection, the herd immunity threshold (HIT) is 75%. For measles, with an R0 of 16, it's 95%. For COVID-19, assuming R0 really is 2.2, it's about 55%.
But. BUT.
That's quick n'dirty. If that's all there was to it, modeling infectious diseases wouldn't allow us to buy our private jets and islands, etc.
What goes into R0, exactly? At the end of the day, it's whether or not an infectious person can sync up with susceptible, unwitting dupes into whom the virus can jump. And the problem with the quick n'dirty is that the model assumes ANYONE who hasn't been infected with SARS-CoV-2 is EQUALLY susceptible.
Newborn babies, chemotherapy patients- are they the same as the people whose pictures they put on vitamin bottles, or Chuck Norris?
Enter a multi-institutional modeling group from Oxford, the NIH, Portugal, Brazil, Edinburgh, etc (1). They make several very sound assumptions: - the most susceptible people will be infected early on (i.e. nursing home residents, our canaries in the coal mines). Therefore the population will be somewhat depleted of them later in the epidemic. - with COVID, you either die or you recover. - individual variation in susceptibility is modeled continuously [for stats people suspicious about categorical variables] - Social distancing is still the best way to reduce transmission and infectivity. - After coming up with their clever equations, they fit the model on Austria and Italy's epidemics, and eureka! it predicted things perfectly!!
Conclusion: as the epidemic whirls on, the effective HIT drops dynamically, down-- at the end-- to only 10%.
And-- for everyone worried about whether or not effective first wave suppression has just left everyone vulnerable, and implies a nearly-as-big second wave once distancing is reduced: the model nicely predicts that removing the "highly susceptibles" from the population in the first wave makes the second wave likely rather muted.
THE MODEL SPECIFICALLY PREDICTS THAT AN IMMUNE FRACTION OF AS LOW AS 20% MIGHT SURPASS THE EFFECTIVE HIT.
This is why we can say, with some degree of hope, that NYC's 21% serosurvey antibody results might really, truly, be substantially close.
It's also why we can reasonably hope that places with smaller epidemics and lower prevalence might have muted second waves.
THE US IS NOT EXACTLY A MODEL NATION
Feeling frustrated with models? Yes, it's true, they set unrealistic expectations for appearance and hoard all the celery. Ah, the other kind? The one with numbers? Well, that kind is still very, very valuable.
Models are like judgy strangers on the internet: it's all in the assumptions. Their core parameters (called "assumptions") are as important as the way the variables are arranged in the equations.
And remember the more data which rolls in, the better the assumptions and the tighter the fit. Rather like quarantine jeans.
So why did some models overshoot, and some under-call? What do we know today that we didn't know 3 months ago?
- Asymptomatic transmission drives at least half of all transmission events [NOT assumed in the "cases are the cases" models] - Some asymptomatic transmitters eventually become symptomatic [NOT assumed in the rosiest 'Big Denominator' models] - The confirmed case count, especially in the first 2 months of the epidemic, was essentially a work of fiction and underestimated true cases by a factor of at least 10- potentially 50-80 [models like IHME took the US and international case counts as gospel] - Deaths have been missed and under-counted [NOT assumed by basically everyone, since deaths are the most reliable number] - The US is substantially sicker than the first nations on whose epidemic curves we modeled, so more people died than expected - The upslope of the curve is much steeper than the downslope, where case counts linger like bad party guests (China's- our first example on which to model- was artificially ski-slopey).
And we know so, so much more about the basic pathology of the virus, and our immune response, and also about meth-addicted private zookeepers.
SOURCE
M. Gabriela M. Gomes, Rodrigo M. Corder, Ricardo Aguas et al. Individual variation in susceptibility or exposure to SARS-CoV-2 lowers the herd immunity threshold. https://doi.org/10.1101/2020.04.27.20081893
Isn’t a vaccine essential forced herd immunity?
Great, another model (theory, hypothesis), this time on the rosy-scenario side instead of the doomsday side.
I hope this one is right.
It’s possible there is something to this. I’m using Spanish Flu for a reference.
“The 1918-19 Spanish Influenza Pandemic and Vaccine Development”
September 26, 2018
https://www.historyofvaccines.org/content/blog/vaccine-development-spanish-flu
“First, the numbers. In 1918 the US population was 103.2 million. During the three waves of the Spanish Influenza pandemic between spring 1918 and spring 1919, about 200 of every 1000 people contracted influenza (about 20.6 million). Between 0.8% (164,800) and 3.1% (638,000) of those infected died from influenza or pneumonia secondary to it.”
So, with no vaccine, and no 2/3 of the population infected and recovered typically understood herd immunity, Spanish Flu faded out.
So the new model might be right.
No. See above. There was no vaccine for Spanish Flu, and it still disappeared with only 20% infected.
Beck said herd mentality yesterday when he meant herd immunity, but then again, herd mentality sums up the cdc handling of the pandemic...
i am all about the herd immunity... bring it on.
For me, “model” is a dirty word. They destroyed the usefulness of the concept with Global Warming.
vaccines have never been “forced”.
Bump
As I keep saying, Dr. Fauci is not the only M.D. with an opinion on this virus.
And frankly he’s far from the most credible.
“vaccines have never been ‘forced’.”
Were parents given a choice when we school kids were given shots and sugar cubes?
Nope. The virus only has to run out of easy hosts.
And, this herd immunity will cost us how many lives? Because coronavirus isn’t even close to being over.
I've seen numbers that put the R0 for coronavirus at 18. That's a scary thought.
At this point far less than if we lift the lockdown completely and follow simple hygiene rules. Forced isolation of sick people is called quarantine. Forced isolation of healthy individuals is called tyranny. You are free to stay in your house forever if you so choose, just don't mandate that for others.
When you count every respiratory illness (non-Covid) death as Covid fatality, you can really inflate your numbers. This is what the CDC has been doing. Over 571 additional deaths every day. Plus NY and other areas tagging every death as Covid, you can’t believe anything.
I totally agree with you on this. But, in reality, what I'm seeing here is rampant irresponsibility when it comes to not spreading this virus. People here are acting like it's gone, and the count keeps going up.
You presume “only 20% infected”...
“vaccines have never been “forced”.”
Yet, and depending upon your definition of “forced”.
Yes, indeed. I was never given a Smallpox vaccination, at the choice of my parents, on the advice of their doctors.
I couldn’t remember if parents had to approve vaccines or not back in the ‘50s and ‘60s. (Why would I? I was a kid.)
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