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Old 03-28-2020, 10:58 AM
Stranger On A Train is offline
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Join Date: May 2003
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So, this thread seems to be going down a familiar path of being more about personally disproving me than a factual discussion about the issue at hand, so I am going to bow out of the thread but I do want to address a few of the points of DSeid's post in as even and rational a manner as possible.

Quote:
Originally Posted by DSeid View Post
Stranger - you seem to know more than the experts -

- Who do NOT believe that aerosols are a significant factor in transmission (mostly droplets).
I have not said and do not believe that I "know more than the experts". I do enough to know that the official numbers about the replication rate--based on data reported from China, and on infection reporting rates in various countries all of which lack comprehensive testing for even symptomatic cases--is not consistent with what we are seeing in terms of how quickly and widely the epidemic has spread, and how rapidly cases are appearing en masse. This isn't an issue of health officials deliberately misleading the public but simply a lack of objective data upon which to base a firm estimate.

The range of transmission rates that I estimated--which was based upon some speculative modeling that tried to reproduce the trends seen in the first weeks of reported cases in the US, and thus, is neither precise or firmly grounded enough to take as anything but a caution--was based upon the very sparse data available at the time and while I haven't bothered to update it because the data we have now is even more unreliable in reporting total infections due a criminal lack of testing it is clear that both that there are a lot of asymptomatic and marginally symptomatic cases which have at least been qualitatively verified by testing, and that the mode of transmission cannot simply be by intimate contact or fomite transmission that would support this rate of expansion, and droplet transmission would require carriers to exhibit symptoms (coughing, sneezing) in order to distribute droplets so widely.

That we are now seeing significant numbers of medical personnel who are becoming infected despite wearing all recommended PPE which would indicate that the normal measures to prevent fomite and droplet transmission are not adequate. This is also indicated in the transmission on the Diamond Princess where the contagion continued to spread even though passengers were confined to quarters and the crew were asymptomatic, suggesting that either the crew or the HVAC system were facilitating spread despite the isolation and hygiene measures in place. There is evidence that closely related SARS-CovV(-1) virus responsible for the 2002-2004 outbreak could be transmitted by aerosol modes, so this is unsurprising.

Quote:
Originally Posted by DSeid View Post
- Who understand that herd immunity is NOT something that only applies to endemic diseases and is a critical part of modeling the dynamics of every epidemic or pandemic. Local herd immunity is what broke the spread of Zika in Brazil, for example. Herd immunity is what happens under a flatten the curve scenario as well, just slowly and controlled enough to avoid overwhelming the healthcare system at its peak.
The Zika virus is primarily spread by mosquitos with a secondary mechanism of intimate contact (unprotected sex), and of course from mother to fetus. I haven't been able to find a reliable estimate for the replication rate of Zika but because it resides in an insect host it is considered endemic, and the massive concern about it during the 2016 Rio Olympics was less that there would be an unconfined outbreak that would spread to nations in temperate areas than that it would be unknowingly contracted by attendees and athletes and lead to a series of miscarriages and congenital brain abnormalities such as microcephaly in the fetuses of pregnant women.

Herd immunity prevents the uncontrolled spread of disease but as long as there are reservoirs--and we don't really know endemic the SARS-CoV-2 virus is going to be in the population once this epidemic wave is over, or whether additional epidemics may recur--and the virus is extremely contagious (which SARS-CoV-2 gives every indication of being) this does not protect at-risk individuals from the potential for being infected. This is why despite recommending that the vulnerable (very young, elderly, and immunocompromised) are recommended to get the annual influenza vaccine the are still warned to take measures to prevent infection and to self-isolate during regional flu outbreaks. We don't actually know how long or how well acquired immunity or hypothetical immunization will limit the virus in the future (although there are some indications that the virus does not mutate fast, which if true is hopeful), but regardless, those people who are in at-risk demographics are going to have to maintain isolation for an extended period of time until widespread antibody testing is available and there is a clear indication of how many people could still carry and transmit the virus.

Quote:
Originally Posted by DSeid View Post
Who understand that good confidence intervals do not require testing 5% of the population with decent random sampling techniques. In fact the WHO protocol for such studies (see section 4.1) discusses the 95% confidence intervals with just 100, 200, and 300 samples at different levels of true seroprevalence.
Small sample sizes are statistically representative of a homogeneous population, but the United States is not one big bag of interchangeable marbles that we can estimate from a small sample size. We see now that not only do affected cities have different rates of COVID-19 incidence but the demographic distributions (age, sex, wealth) are distinct as well, with the only real commonality that young children without underlying conditions have almost no incidence and the mortality starts to ramp up dramatically after age 60. Every public health official I have seen talk about dealing with the issue of limiting and ending the epidemice has specifically called out the need for wide scale testing to get a handle on how big the problem is and how many people may be immune.



Quote:
Originally Posted by DSeid View Post
Nevertheless to THE HYPOTHETICAL that cmosdes posed - yes, experts (like Mark Lipsitch) believe that for this virus 50% of a population immune/resolved would be sufficient to achieve herd immunity and stop spread (go to 9:20 on, especially at the 10:55 mark). Lipsitch takes pain to point out that case fatality rate is not the same as infection fatality rate and that we simply do not know what the latter is. Note he offered other social distancing option than full hammer approach as possibly effective.

IF, theoretically but with some reason to believe, children functioned the same as those resolved, then the 21 to 27% (depending on if you want to define child as under 15 or under 19 yo) of NYC that are children, get you halfway there. IF, also theoretically but with some reason to believe, there are 8 asymptomatic to symptomatic ones, then herd immunity and flattening of the growth would occur when symptomatic (not confirmed) infections reached about 270,000. Which would be by three weeks later would have 2700 total deaths before the daily death rate started to slow down. Which would be in a week, and would correspond with ICU admissions slowing down within the next few days. Which of course might occur due to social distancing beginning two weeks ago as well.
I haven't been able to view the video you linked to in the subsequent post because the website keeps hanging and reloading so I don't know when the presentation was made, what data it was based upon, or how the conclusions were arrived at but if this is Dr. Mark Lipsitch of Harvard School of Public Health, I would certainly acknowledge his expertise in this area as a primary authority. In this interview on 02 March he indicates that the ultimate global infection rate may be 40%--70%, so at least of that time he clearly didn't seem to feel that 50% would be the limiting threshold after which herd immunity would effectively limit further transmission.

As for assuming that if all children are immune that conveys half of the supposed 50% threshold for herd immunity, that just isn't the way herd immunity works. That distribution has to be spread across the entire demographic such that there is no large scale transmission between anyone. If all children are immune but, say, middle-aged stockbrokers are generally not, then you will still see an epidemic of middle-aged stockbrokers transmitting and contracting the disease. This is, again, why wide scale testing is crucial to be able to track the amount of infection and immunity so we can know when lockdown and isolation measures can be lifted without great risk of another epidemic wave.

Despite all of the bad news we are seeing now in New York and New Orleans (and soon in Los Angles, Chicago, and essentially every large and mid-sized city in the United States), and in other countries around the globe that have not acted promptly to limit contagion and prepare for the onslaught of COVID-19 cases, there is some good news. The case fatality rate is about 1%-2% overall for people exhibiting serious symptoms of COVID-19, so while millions of people around the world are going to die (many of whom could be saved if medical care was available), this is not an existential threat that is going to disrupt food production and logistics in developed nations. It is a major catastrophe for developing nations and those with very dense and impoverished populations where quarantine is not possible and medical services are limited to non-existent. While front line medical personnel have limited and inadequate PPE and are getting hit with serious infections of their own, those who do survive will be able to treat patient using less effective PPE, and if immunity can be demonstrated and verified with testing, people who have been unemployed may be able to be trained in basic patient care and non-care duties to free up nurses to focus on more critical care duties. And there are indications that the virus does not mutate rapidly which may mean that an eventual vaccine and immunization campaign make eradicate the virus or at least render it sub-endemic such that outbreaks are rare and sporadic rather than periodic or seasonal.

I'm going to bow out of this thread now so the discussion can continue without the toxicity of just trying to prove that I'm wrong in my estimates (which is entirely possible given the poor data and speculative method) or that I'm not an expert (absolutely true, and an impression I never intended to give) and therefore what I say must be wrong. I would ask that others use evidence and fact-based reasoning with the acknowledgement that we are short on data and even the most vaunted experts lack the complete picture to make exact predictions on where this will go and how long it will last, which I think all of those experts have made clear in their qualified language and discussion of the unknowns.

Stranger

Last edited by Stranger On A Train; 03-28-2020 at 11:02 AM.