Ok, dumb idea time: suppose that everyone in an office sits on a chair that raises their body to X volts. At the same time a collector mesh is provided at each desk, at -X volts, but shielded so that you can't touch it and shock yourself.
What X is large enough to ensure that all the virus particles you cough out end up at the collector? Is it possible to do this without electrocuting everyone?
The mass difference between humans and viruses is something like 10^19.
So if you take the naive approach -- which is wrong, because charges live on surfaces, not in volumes -- you would want the person to have about a coulumb of charge to ensure that 1 extra electron was allocated to each virus particle.
Whether or not 1 electron per virus is enough is a separate question, but that gives you a lower bound -- if you are allocating, say, 0.1 electrons, only 10% of your virus particles will have a charge.
Edit: so, given the capacitance of humans as 200 pF, that would be 5 gigavolts?
Using the size of aerosolized droplets (0.35-10um) and the mass of human skin (20 lbs) would knock two orders of magnitude off, and drop the floor estimate to 50 megavolts.
For anyone wondering what a 50MV source looks like, one was actually built out in the desert near Joshua Tree in '54. Strangely, it was built for longevity research. Well, that and UFOs and anti-gravity, because of course:
"The Multiple Wave Oscillator is a combination of a high voltage Tesla coil and a split-ring resonator that generates ultra wideband electromagnetic frequencies."
The ionization of the air in the main room was quite intense, with plasma freely forming coronas.
Once the pandemic is over, you can drive out to get a 'sound bath' in the room, if you are so inclined.
Re: capacitance, our capacitance is too low. The higher the capacitance the lower the voltage. A 1 farad capacitor could hold 1 coulomb of charge at 1 volt of potential difference. A 0.1 farad capacitor could hold 0.1 coulomb of charge at 1 volt, or 1 coulomb of charge at 10 volts, or 0.01 coulombs of charge at 0.1 volts, or 100 coulombs of charge at 1000 volts.[0]. Because our capacitance is so low, you need a huge amount of voltage to force all of those electrons onto us.
[0] Assuming the capacitor didn't fail -- in the case of actual capacitors, they only operate within certain parameters and tend to explode outside of them, in the case of people in an atmosphere, you'd probably see those discharges well before you managed to shove a full coulomb of charge onto one.
Free electrons tend to distribute themselves on an object as to minimize the repulsive forces between them. This usually means that they distribute evenly on the surface of objects.
Humans are a bit more complicated in structure than say a metal ball, but my guess would be that there would be a similar situation where all the free electrons would just build up on the skin. Therefore, I don't think the particles one would cough up would be negatively charged.
Alveoli are basically small air sacs in your lungs, so they're a surface (it's just an inverted ball, a hollow sphere in a not-so-solid object).
No idea how that influences where the electrons go.
I wonder how the nervous system would interact with that as synapses fire. I'm curious if they would build up, or if the synapses all over the body firing would make them bounce around constantly.
> Alveoli are basically small air sacs in your lungs, so they're a surface
> No idea how that influences where the electrons go.
Electrons don't specifically move toward surfaces, they move to be as far apart from each other, so internal surfaces don't count significantly. Saying they move toward surfaces is only true for convex objects (and they are evenly distributed when the object is a sphere).
In the human body, they'll move toward extremities: hands, feet, tips of hairs, ...
The latter is an easy to observe effect of static electricity, charges will apply pressure on the hairs and make them straight so they are as far away from the rest of the charges as possible. See the first image here for example: https://www.loc.gov/everyday-mysteries/item/how-does-static-...
This seems to assume that virus particles are charged. If they are neutral, they wouldn't be driven in any direction by an electric field. Am I missing something? Is it known that virus particles have a charge?
I think you are missing the OP's assumption that by raising the subject's entire body to +X Volts, any virus particles they breath out will start out with this same positive charge. I'm not sure this assumption is true, but it seems plausible.
If DIYing, choose your UV wavelength wisely. UVC (around 254nm wavelength) is germicidal and doesn't produce ozone (it actually dissociates ozone). "Vacuum UV" (in the range 185nm) converts oxygen in the air to ozone, which is highly toxic.
I always wondered just how much UV-C do you need to effectively kill the virus (power vs duct diameter and air speed).... because, instead of traditional masks, you could take a small fan, blow air into a pipe with a UV-C bulb inside, and pump the sterilized air to the human... basically something like this: https://www.youtube.com/watch?v=fzGrh2io9Ds&app=desktop
I tried looking into that this spring. I suspect the answer is for this virus not much. Nothing to indicate that any part of it's life cycle involves hanging around latent.
Interesting thing bacteria and some viruses have DNA repair enzymes that can fix damage from UV-C. Medically you're always bedeviled by bacterial and fungal spoors.
Limitations with UV-C sterilization I think prevents wider use. Not a magic bullet. Though it probably works well for influenza, colds, and this bat virus.
Yes, far UVC, 222 nm, won't penetrate your skin far enough to get to living cells and can be used around humans safely. It's a new technology, though, and not widely deployed.
Also light has very complex interactions with various of our biological symptoms, and I personally would be wary of unintended consequences without long term testing. e.g. it could interfere with sleep, or have other subtle effects
Any HVAC company can install this for you right now, or you can buy a kit and do it yourself. A UV light bulb to install in your central air system is an off the shelf product. "Whole house UV air purifier" as a search term will pull these up.
Are these products actually effective though? I mean the duration and intensity required to kill viruses in moving air must be quite high? Or is it just snake oil, like how a lot of hand dryers have bluish/purple LEDs (which emit no UV) that shine on your hands?
Yes, they're effective. But near-UVC is dangerous to your skin and eyes, so it absolutely must be shielded. Far-UVC is quite safe to humans, and just as effective against coronaviruses, but it's rather expensive at the moment.
I can’t speak to their effectiveness in air, but they work very well for e.g. bacteria in rapidly flowing water. Aquariums have been using them for as long as I can remember.
It's important to remember that your immune system is improved by coming in contact with common viruses. This is even more important for kids.
There's evidence that people that have been exposed to previous, weaker, coronaviruses are more likely to have mild responses to Covid-19, for example.
It isn't very practical, as long as you don't worry about getting the virus from the outside in, which would be an unusual thing to worry about for home owners.
Just vent it out in the open air and not on people.
Et voilà, now it's no longer terrible for efficiency since you're recovering 70-90% of the energy. For fixed-plate exchangers there's no cross-contamination, either.
There are plenty of products for both HVAC and plumbing that use UV-C. The new hotness is 405nm because it’s safe around humans and there are already under cabinet lights for kitchens and overhead recessed lights for bathrooms, etc.
Looking at germicidal bulbs at 1000bulbs.com, the highest wattage bulb they have is 65 watts [1]. Most are well under that.
Looking at random in-duct systems, it looks like they range from 1 to 10 or so bulbs with the later being for commercial buildings. Home systems seem to lean toward 1 or 2 bulbs of maybe 20ish watts or so total. This site [2] says typically $15-30 per year energy cost
Nope. I would much rather have a good filter than mechanically removes infectious particles, wildfire smoke, and particulates in general.
For a residential recirculating system, the relevant parameter is flow rate times fraction of particles removed in one pass. An AC or heater generally has a high flow rate and needs a filter to keep the heat exchanger and fan clean regardless. The added material and energy cost of a good filter is low.
On the other hand, if you are moving air from one space to another and don’t want to contaminate the space you’re moving air to, the absolute filter / sterilizer efficiency may matter. Things like HEPA may be useful here.
I would be surprised if a UV lamp is cost effective for new installation. For retrofit in a system that can’t handle a better filter, maybe.
Germicidal irradiation via UV light on HVAC is just not possible. Due to the amount of energy it requires to be effective is ridiculously high.
https://www.climask.com.tr is interesting. Like a face mask on AC unit.
Nano-silver is effective against bacterias and viruses. And having a filter with nano-silver coated surface is just a simple yet an effective approach. Cost-wise changing a good quality air filter every 2-3 months is much cheaper than having a UVGI installed and paying higher electricity bill every month.
> they constructed an air-tight closed ventilation system that connected a six-room tuberculosis ward to an exposure chamber with 150 guinea pigs. (Among rodent animal models, only guinea pigs could cough and sneeze, making them ideal for studying how respiratory diseases spread.) The guinea pigs were exposed to the infected air over a four-year period. A second group of 150 guinea pigs acted as controls: their air ducts were irradiated with UV-C lamps to kill TB bacilli.
Results:
> an average of three guinea pigs per month contracted TB, while no controls were infected. The experiment [also] quantified how many TB infections could be expected to result from exposure to a given number of patients over a defined interval.
Relevance to COVID-19:
> Riley’s research points to wearing masks and disinfecting air in enclosed spaces as two of the most effective tools for fighting COVID-19
> The animals were used so frequently as model organisms in the 19th and 20th centuries that the epithet guinea pig came into use to describe a human test subject.
- It contains no experimental data, it's a review of possible methods.
- It's not about Covid-19, although that's to be expected.
- The masks it talks about are N95 and N100 respirators (which it notes aren't in adequate supply).
Some interesting quotes:
> If one assumes that influenza is transmitted by respiratory droplets [..] rather than by aerosols [..], the supposition may be that keeping a safe distance may obviate the need for a mask. It is stated that the range of such droplets is generally no more than 3 ft. We are unable to locate the basic science behind that assertion.
> Whether contagious as a respiratory droplet, aerosol, or both, there have been no controlled studies to investigate the efficacy of respirators in preventing the transmission of influenza A
> there is a theoretical problem in the logic underlying N–95 respirators. Assume an N–95 mask functions better than its rating and at a sedentary inhalation rate blocks 98% of the bioaerosols that it is confronted with. We are still left with the 2% that penetrate through the filter, to be inhaled by the wearer. Whether discussing tuberculosis, influenza, measles, or smallpox, we do not know the concentration of pathogenic bioaerosols in the environment, nor do we know the minimum infectious dose for these pathogens.
Anyway I don't think anyone disagrees with their conclusion that having everyone wear N100 masks is a good idea, but I'm not sure if any of their proposed methods are feasible. And the most important conclusion of their research is perhaps that we know way too little about possible countermeasures.
It requires you wear the mask at all times. And that you change it regularly by removing folding inwards and disposing securely.
Otherwise you may pick up an infection and then put a mask on afterwards which necessarily means that much of the shedding caught in the mask will be breathed back in - From mouth to nose and vice versa.
Or put the mask back on backwards or wave it around in the air, put it on surfaces and the like.
All of which amplify the current infection you have making you more infectious when you take the mask off.
And may explain why at a local Covid secure school they all went down with the usual back to school viral cold far more rapidly this year than they normally do.
What we don’t know - because we’re not hamsters permanently in cages - is what the network effects are.
For all the talk about how much masks help, I haven't seen great studies that aren't in vitro, not specifically in health care settings, and not specifically around someone known to have it. I found this which is at least a natural experiment:
> Mandating face mask use in public is associated with a decline in the daily COVID-19 growth rate by 0.9, 1.1,1.4, 1.7, and 2.0 percentage points in 1–5, 6–10, 11–15, 16–20, and 21 or more days after state face mask orders were signed, respectively.
I'm trying to sort of if those percentages are absolute or relative. I think they're absolute because some of the graphs are labeled "percentage point change," but using absolute percentage point changes for an analysis like this is seriously flawed because a 2% reduction could range anywhere from a miracle to statistically significant, but negligible.
It's also not clear if people feel safer wearing face masks, so they engage in riskier activities.
My guess is they're not as effective as claimed because while the Bay Area has pretty high compliance, if masks were systemically very effective, we'd see case rates drop a lot faster, not still be above mid-June numbers. That said, whatever the Bay Area is doing right now is working.
From this experiment you might say something about disinfecting air, but the guinea pigs weren't wearing masks. What you are testing, if anything, is the efficacy of "UV-C lamps to kill TB bacilli".
Wearing masks is an entirely different thing, and would need an entirely different test.
Even the original experiment leaves questions for me. How does one diagnose TB in guinea pigs? What health state were the guinea pigs in? Was there a familial predisposition to respiratory illnesses for some of these? What conditions were they kept in? Etc.
Can we "mutate" a virus to use radioactive isotope of carbon (c-14? something that is not harmful for humans) so that we can observe how viral a virus is?
Not an expert on radio isotopes or spectrography or viruses.
Note: I know, radioactive virus at this point might freakout people a little.
We basically already know how viral viruses are because they undergo mutations, and we can trace which strain people have and where they caught it from by sequencing their DNA (technically RNA) and looking for the virus's "ancestors".
Also you wouldn't mutate a virus with C14 or similar radiactive isotope, because that can't be encoded in its genetics, and such a virus would use any old Carbon atom (most likely normal C12) to replicate.
Finally, mutating a virus and releasing it seems ethically dubious in the middle of a pandemic...
The article says the TB experiment ran for four years. It isn't clear that you need four years to prove airborne transmission, but it is likely that you need a lot of time.
Scientists have already published work confirming the virus is airborne stable and viable for many hours.
I don’t know why there hasn’t been more discussions about the consequences of this though.
For example, with airborne transmission, 6 ft distance is not enough, you need > 30 ft, e.g. if you are inside with poor airflow for a long time with someone who is infected, good luck (unless you have a good N95).
It's pretty much settled also for sars-cov2. A study in China found the virus in air samples taken inside the central air-condition system, far away from any patients (see bottom).
Another found correlation between infected and where they were sitting vs AC duct outlets.
Also the fact that mandatory masks have had zero effect on the R value in any country, same as for influenza and other "flu" viruses.
If it was spread by droplets/surfaces then masks should at least have some effect to slow or contain the spread, like make a dent in the curves.
Yes there are masks that prevent TB transmission but this bacteria is more than 10x larger than typical respiratory viruses. They look like duck beaks, are very uncomfortable and require training to use properly.
I haven't seen these anywhere during this pandemic and they wouldn't help either as they are designed to prevent aerosols down to about 2um size.
There is plenty of space for ~0.1um viruses even in 0.5um droplets. Some researchers even claim the virus can stay potent a while after the droplet evaporates and float around like dust.
It's funny how some claim we didn't need masks before, but now we need them since it's spread by aerosols??
The truth is in fact the opposite and don't get me started on cloth masks...it's absurd. This seems more like covering their asses than following the science.
Most of these studies involve health personell, with high-end masks, the general public will of course do much much worse.
This survey of studies and history of mask use in dentistry is also informative (why was it taken down?): https://archive.is/My2jr
The WHO reversal on mask use is also revealing:
On July 12, Deborah Cohen, the medical correspondent of BBC2’s Newsnight, revealed on Twitter that: ‘We had been told by various sources [that the] WHO committee reviewing the evidence had not backed masks but they recommended them due to political lobbying.’ She said the BBC had then put this to the WHO, which did not deny it.
In March, the WHO had said: ‘There is currently no evidence that wearing a mask (whether medical or other types) by healthy persons in the wider community setting, including universal community masking, can protect them from infection with respiratory viruses, including Covid-19.’
-Van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020;382:1564-7.
-Fears AC, Klimstra WB, Duprex P, Weaver SC, Plante JA, Aguilar PV, et al. Persistence of Severe Acute Respiratory Syndrome Coronavirus 2 in Aerosol Suspensions. Emerg Infect Dis 2020;26(9).
-Chia PY, for the Singapore Novel Coronavirus Outbreak Research T, Coleman KK, Tan YK, Ong SWX, Gum M, et al. Detection of air and surface contamination by SARS-CoV-2 in hospital rooms of infected patients. Nat Comm. 2020;11(1).
-Guo Z-D, Wang Z-Y, Zhang S-F, Li X, Li L, Li C, et al. Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China, 2020. Emerg Infect Dis. 2020;26(7).
-Santarpia JL, Rivera DN, Herrera V, Morwitzer MJ, Creager H, Santarpia GW, et al. Transmission potential of SARS-CoV-2 in viral shedding observed at the University of Nebraska Medical Center (pre-print). MedRxiv. 2020 doi: 10.1101/2020.03.23.20039446.
-Zhou J, Otter J, Price JR, Cimpeanu C, Garcia DM, Kinross J, et al. Investigating SARS-CoV-2 surface and air contamination in an acute healthcare setting during the peak of the COVID-19 pandemic in London (pre-print). MedRxiv. 2020 doi: 10.1101/2020.05.24.20110346.
-Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, et al. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature. 2020;582:557-60.
-Ma J, Qi X, Chen H, Li X, Zhan Z, Wang H, et al. Exhaled breath is a significant source of SARS-CoV-2 emission (pre-print). MedRxiv. 2020 doi: 10.1101/2020.05.31.20115154.
-https://pubmed.ncbi.nlm.nih.gov/19797474/
-https://pubmed.ncbi.nlm.nih.gov/19216002/
And indeed you can sympathise with them that it would be hard to perform such an experiment.
But the whole point of science is that it allows us to make predictions based on theories. And the current scientific consensus is that wearing masks is beneficial.
> ultraviolet-C disinfection technology for air purification systems that were installed in health care facilities, factories, and NASA space capsules. Today, this technology is being used in Shanghai, Moscow, and New York City to protect subway and bus passengers against SARS-CoV-2, and China is also using the technology to disinfect hospitals
Russian FSB has just arrested (on secret state security charges) on his short trip back home from China a top high voltage systems specialist who has been working for the last two decades on UV water and air cleaning system in South Korea and China. Seems it is becoming a sought after hot tech in the current situation.
I have an ozone vegetable washer. Is it dangerous to be in same room when this vegetable washer is running ? I can smell the odour of ozone near the vegetable washer
The odour detection threshold is 0.005-0.02 PPM. OSHA says less than 0.1 PPM over an 8-hour period.
So you can smell ozone well before it is in the harmful range. Some air circulation wouldn't hurt while the device operates, but napkin math says you are OK.
Resolution of plain optics only goes up to the diffraction limit, which is not enough to see a virus.
Then there are super-resolution techniques which can go beyond that, but I don't think any of them could be adapted to scan the vicinity of the coughing human in real time.
This quote from the report should be top of the list of the lesson-learned from this COVID pandemic:
> The current guidance from numerous international and national bodies focuses on hand washing, maintaining social distancing, and droplet precautions. Most public health organizations, including the World Health Organization (WHO) [16], do not recognize airborne transmission except for aerosol-generating procedures performed in healthcare settings. Hand washing and social distancing are appropriate but, in our view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people. This problem is especially acute in indoor or enclosed environments, particularly those that are crowded and have inadequate ventilation [17] relative to the number of occupants and extended exposure periods (as graphically depicted in Figure 1). For example, airborne transmission appears to be the only plausible explanation for several superspreading events investigated that occurred under such conditions [10], and others where recommended precautions related to direct droplet transmissions were followed.
Meanwhile here in Canada they waited until late May to even recommend wearing a mask in such situations (other countries like the US had similar time frames and Dr Fauci openly admitted they withheld this recommendation for the benefit of healthcare workers).
Much like drug prohibition and other grand social control experiments, I'm not convinced the value of being vague or simply straight up not recommending masks in order to keep supply chain available for healthcare workers was ultimately worth the downside.
If supply chains was the issue then spend the government law enforcement power controlling and directing the supply chain for medical quality masks. This 4 month experiment (and I'm being generous there) where Feb, Mar, Apr and most of May they spent creating confusion and not recommending masks ultimately did more harm than good.
Now pundits and online commenters love to attack these anti-mask people when for much of the year expert sources were far from making masks the recommended choice. Including gov-delivered misinformation about their utility in order to explain themselves.
If the pro-social control (ie, lying the public) group thinks it was really stopping the wealthy and connected from completely ignoring these guidelines, then they are lying to themselves. As always with these gov poppet-mastery policies the only losers were the lowest common denominator poor people. Plenty of which still don't funny trust masks.
I would have rather spent four+ months explaining the virtues of masks and explaining the supply problem honestly. Than playing catch up last minute.
The fact Asia who had adopted masks, and never spent any time lying or dodging their public on their utility, have done better than western countries is no surprise. Asian countries had masks well before COVID.
The older I get the more cynical I become about government and intelligentsia 'we know whats best', that includes withholding information (something extra popular in healthcare). All information should be as transparent as possible, regardless of fantasies of controlling it.
It seems the reasoning by officials is, "Yes, it's airborne, but there's not enough N95 masks for everyone so we don't want to cause panic or an N95 mask shortage for doctors and nurses by admitting it's airborne."
Turns out the "don't close borders" advice was a cached thought related to a plague outbreak in India over 25 years ago, and welded in place by politics.
Agreed. US official response has been to lie to the population so as to “not cause a panic” then act shocked when that same population doesn’t trust the officials anymore. Go figure.
Also supposedly if a disease is declared airborne then hospitals have to adopt various isolation measures beyond just N95 that are very costly. This may be the reason the powers that be won't announce airborne transmission until after the pandemic is over.
We make fun of medieval medicine but look at this shit! We're pretending that saying some magic words has an effect on a physical reality of disease spread!
Who says that saying its airborne "has" to mean that certain procedures have to be adopted? That's not a rule of the universe, it's a rule that humans came up with and agreed upon and humans have the power to fix. We distilled down a set of physical principles into a set of guidelines, forgot the underlying physical principles and now operate purely in the world of the manmade guidelines, totally oblivious to when the guidelines are no longer reflecting the physical reality.
While I understand the frustration, the reality is we shouldn’t be making fun of either. Just because the end result of something is inarguably “stupid” does not mean that any of the things that went into it are “stupid.” To do the Hacker News thing and make a bad analogy to computer science topics in a totally irrelevant thread, this is how I view a lot of stuff people complain about these days (think JavaScript, or Electron apps.) Real life is hard.
To be a bit more concrete, consider the following: if you have a system where people are not encouraged to follow the rules as written, they will work against the spirit of what is written as well as what is actually written. If you have a system where people are discouraged from not following the rules, they may still engage in things that do not follow the spirit or written rules, but there is some accountability. But you can also try to work around what’s written to follow the intent as well, and I think that is where you get weird, counterintuitive, “stupid” results that can still “make sense” (as opposed to clearly corrupt cases where it is “stupid” and also does not make sense.)
I think people, especially literal minded as many here are, prefer concrete rules. But the knock-on effect is that its not easy to simply proclaim they’re made up any time it’s inconvenient, and it really shouldn’t be. Perhaps, in fact in my opinion, definitely, the “escape hatches“ for when rules don’t work out practically are broken, but I still do prefer having rigid standards, especially for health.
Hopefully, although it is probably not going to happen, organizations can have some postmortem-style reflections on what went wrong, so that hopefully next time we can be better prepared. History loves repeating though, so, you know.
Keeping information from the public to avoid mass hysteria is one thing, but keeping information from hospitals so they don’t have to implement prohibitive protocols is daft. If the healthcare response would be unreasonable, the right thing to do is to deliberately modify the protocols, not pretend the problem isn’t happening.
In a perfect world, with a responsive and easily adaptable healthcare system ..
Also how do you keep information from the public without keeping it from hospitals. Widespread publicising of a controversial tidbit to hospitals would leak within the minute if not within the hour ..
I'm not saying I agree with how it was handled at all .. I'm merely pointing out the fairly obvious realities to the claims made, which seem strong on principle but lacking in pragmatism and consideration of the realities.
OK. But not caring about how we get into no-win situations is exactly how we get into no-win situations.
Or perhaps in a different light, neither do the people who would've died if we had chosen a different branching path with negative consequences. There is some implication that there was a better outcome easily available and that is not clear at all. There should've been one, but there wasn't necessarily.
Unless you say something like “look it’s airborne but that fact shall not be admissible into any future lawsuits on any topic” (and have certainty that that will stand up to review), I’m not sure you can fully equate to the current “it’s not been declared to be airborne transmissible.”
It seems leaders think “you can’t handle the truth” is a proper response to citizens.
We would have had to prepare with 10 years of 24/6 manufacturing of N95s to stop an airborne virus, which is why the most effective response is social distancing (not going to work, the 6 ft thing is bunk).
Why bother to disinfect when you can ventilate? Air with pathogens out, fresh air without pathogens in.
(Regarding herd immunity: you're aware that at the current rate of 55000 people per day, it would take 10 years to infect 60% of 320 million people? Nothing to say of the countless casualties that you would get in the process.)
Since eradicating the virus has become impossible, most national governments are currently pursuing a herd immunity strategy by default. They're just doing it at slightly different rates.
In the USA the current daily rate of confirmed new cases is about 43000, not 55000. However there are a large number of "dark matter" cases not counted in official statistics. About 40% of infections are asymptomatic, and many more are paucisymptomatic. Most of those patients never get tested.
Agree with "herd immunity strategy by default". Absent a vaccine, about the same percentage of people will become sick, while a larger percentage is exposed but does not become sick. At some point, again minus a vaccine, few enough people will be left as potential replicating hosts, that the virus will not be replicating fast enough to maintain the country's epidemic.
Countries will differ by the breadth of the curve, but not the area under it (adjusted per-capita of course).
On the other hand, if you are one of the countries with a long curve, and an effective vaccine arrives before the end of it, you benefit.
What countries are actually following a strategy to reach herd immunity by having "enough" people fall ill and hopefully recover (having "recovered" does not preclude persisting damages btw!)?
Most countries are rather waiting for a vaccine to become available and try to minimize the number of sick and dead in the meantime without interfering with economy too much.
(54.4k was number of newly confirmed cases on friday 10/2 by the John-Hopkins University btw. I'm aware that the US has inadequate testing [0] and that the real number is going to be a lot higher than this.
A vaccine is unlikely to wipe out the virus for good. They just aren't that effective. We can't wipe out other coronaviruses or the common cold by vaccination even if we wanted to.
It will continue to circulate in the population, just in a less explosive manner. This also means it is possible we will never reach herd immunity in some absolute sense much like we haven't for other coronaviruses.
Only New Zealand, Taiwan, Vietnam, and maybe a couple other countries are actively avoiding herd immunity. Regardless of their public statements, other countries aren't actually trying to minimize the number of sick and dead. The public health measures in place are generally insufficient to contain the pandemic, so I predict that many areas will reach a significant level of herd immunity before a safe and effective vaccine is widely available. We won't know whether that prediction is accurate until about a year from now.
Probably cheaper to slot a component into your HVAC than it is to re-engineer it to draw outside hot air, cool it, and still keep interiors at a comfortable level. (Reverse for winter)
My house has a fantastic filter along with a UV system as well. When I bought the house I thought it was overkill, but now I’m quite happy it’s there.
The amount of heat in the air is small compared to that in other materials; buildings with stone or concrete walls have a sufficient heat capacity that you can ventilate without temperature changing too much. This works less well for buildings with wooden walls though.
Ventilating properly requires discipline though. No tilted/semi-opened windows for prolonged time for example. In winter, heating should be turned off and the windows should be as wide open as possible to minimize the time to exchange air. That's to reduce the loss of heat. 5-10 minutes of ventilating is good enough, usually. We usually don't have air condition here, so I don't know what's the recommended process in the summer.
It's common to ventilate like this in Germany in the winter for example. I know (now returned) former German expats that completely missed this development. They still tilt windows and let the heating run all day long.
US buildings are designed to recirculate most air for energy cost reasons. Ventilation sounds like a good idea, but it doesn't match how things work today because of how stale the air becomes.
(That's why in Silicon Valley large companies have "air consultants" measure the freshness twice per year and report the rate. I've talked to some.)
So my question stands on how and what to do to have more effective air circulation indoors, and what else we should do. And why is this conversation only happening several months into a lockdown. It's as if American government is falling down from learned helplessness.
I was thinking HEPA filtration may already cater for virus's, but with HEPA certification being .3 microns and the COVID-19 virus 0.12 microns, then it gets down to individual air conditioning systems. Some may use ionising in combination or UV.
So I foresee a whole raft of legislation and requirements for office spaces ahead. Which will only help drive the work from home long-term as cheaper office space. But also help shift us away from open plan offices that I've never met anybody who liked.
As for herd immunity - that really is best effective against viruses that do not mutate that quickly. Corona-viruses from my understanding, do mutate. Though it is often the case that mutations of a virus over time lean towards mutations that make them less impacting upon the host. Which may be down to natural selection in that those with no impact can spread it more and no virus really wants to kill the host. Impacted/dead hosts tend to be less effective in transmission. So may very well be down to that aspect in why they tend to become less impacting.
On the UV aspect https://www.nature.com/articles/s41598-020-67211-2 a UV wavelength of 222nm that is effective against the virus and safe for humans. Though how stable current UV output is and by that if you had a 222nm light, over time would that drift and become less human safe is something I'd want to check.
There again - flu's and colds are more prevalent during winter months when we have less sun and less UV. Can't ignore that pattern.
> but with HEPA certification being .3 microns and the COVID-19 virus 0.12 micron
HEPA can filter sub-0.3-micron particles, and the effectiveness trends to be even higher than its performance at 0.3 microns.
Although it's not certificated, but it's often true from a practical standpoint, due to the physics of mechanical filtration in general. The reason of using 0.3-micron in certification, is because it's the point where HEPA filters are the least effective. 0.3 um is the most difficult size to filter. Effectiveness goes up at both ends.
The effectiveness of HEPA filters trend to follow a U-shaped curve [0]. Below 0.3 um, particles are captured by the diffusion mechanism. Above 0.3 um, particles are captured by the interception and impaction mechanism. Around 0.3 um, neither mechanism is effective, and efficiency reaches a minimum.
> Corona-viruses from my understanding, do mutate.
Already, reinfection by different strains of COVID-19 has been documented (by DNA sequencing) in Korea. The more people who catch COVID-19, the greater the space of possible genetic mutations can be explored. Some of those mutations may decrease severity, but others are likely to merely increase the presympomatic contagiousness period.
All viruses mutate, but so far SARS-CoV-2 has been mutating relatively slowly. It has an error correction mechanism which blocks the majority of mutations. By contrast influenza lacks that error correction and mutates much faster, which is why we need a reformulated vaccine every year.
The human species already has a significant level of herd immunity against four other endemic coronaviruses. The same thing will eventually happen with SARS-CoV-2 one way or another, but hopefully we will have an effective vaccine soon enough to accelerate that process while minimizing the death toll.
> By contrast influenza lacks that error correction and mutates much faster, which is why we need a reformulated vaccine every year.
That's true, but that might change soon (the "every year", not the mutation speed): Results of [0] are supposed to be published this quarter. I am hopeful for them to be positive.
Thankfully you missed that the article discusses history from 1956 regarding the airborne transmission study methodology. Otherwise you might have gotten a heart attack. Goodness!
And remember all that "all scientists say masks dont work, why are you wearing a face mask, are you stupid?" only to change to the exact opposite in may/june ?
The idea of respiratory viruses not being airborne sounds silly. What's the viral charge supposed to do, not jump into droplets smaller than certain size?
Of course they are present in the smallest droplets! They are present in the mucous secretions of the infected individual and they will get expelled through the big and the small droplets.
The distinction shouldn't be a qualitative one, airborne vs not airborne. It's a quantitative one, sufficiently infectious viruses may pose a risk at much smaller doses, the kind that you may be exposed by the smallest droplets expelled that simply stay afloat.
It's also worth noting that human immune response is a complicated beast, what may not be infectious for an average healthy individual may put down someone with a weakened immune response. So even supposedly "not airborne" viruses that are very unlikely to infect the average healthy individual at very small doses may pose an "airborne" risk for individuals with a weakened immune response.
There are more factors in all of this, atmospheric conditions may play a role. For example, cold temperatures may be more suitable for the virus to remain infectious outside of a host, thus increasing the likelihood of "airborne" propagation.
TL;DR: The distinction between airborne and not airborne viruses is an artificial one. That only makes sense statistically for an average individual at certain atmospheric conditions for a concrete strain of the virus. But as any real-world statistical distribution there are tails and you will find "airborne" qualities for pretty much any respiratory virus in those tails.
What X is large enough to ensure that all the virus particles you cough out end up at the collector? Is it possible to do this without electrocuting everyone?