How is this going to affect so many?
March 22, 2020 3:18 PM   Subscribe

If 40-80% of population will contract SARS-CoV-2 when and how will this happen if we are isolating now?

I'm having a hard time understanding how so many will contract coronavirus when we are distancing and staying indoors. I am aware that not all are distancing but a great majority are it seems. I understand we are distancing now as to flatten the curve and not overwhelm healthcare system.

My county in Florida has 12 confirmed cases. Yesterday it was 10. As of yesterday only 75 tests were performed. Let's say that there are actually only 12 cases, won't the chain of transmission slow considerably if everything is closed and 12 people are isolating? You hear that the rate is growing exponentially but there seems to be a slowing nationally over the last two days. Or can we not rely on "slowing" as fact if there isn't enough testing?

Say we stay indoors for a month and transmission slows but the chain of transmission is still alive. When we all go outside again and live our "normal" lives is this when the rate of transmission will increase again? How will this happen? At the tail end of isolating you would need people who are still shedding virus to be out in communities. Won't there be considerably less people with virus if we are indoors and affected people are isolating and recovering?

I guess there are health care workers and other people that can be spreading all along to family members and such and those people can spread but not as much because we are coming in contact with less people outside of family because no school or work and social-distancing is being practiced. I understand one person typically infects 2 point something people but won't that be slowed if we are inside?

I understand that the chain of transmission slows or stops when there is nobody left to infect because of herd immunity or isolating or mutating away from humans but I'm wondering how it's going to potentially get to 80 percent if there are shelter in place and distancing measures and less people have virus to transmit? Will this happen gradually and over time until we get to 80% or whatever percentage it may be? When hospitals are no longer overwhelmed is then when most will contract?

I am having a hard time understanding. Thanks for answers.
posted by loveandhappiness to Health & Fitness (25 answers total) 9 users marked this as a favorite
 
There are current experts who expect us to have to do serious social distancing for a minimum of 18 months, when they think vaccines may become available.

If they successfully prove that you cannot be reinfected there may be a point when you will only be released from isolation when you are serologically positive, but if that occurs people who are immune because they already had it will get out before the rest of us.

This is part of why they are violating serious ethical guidelines with the vaccine testing - we need vaccines to save our economy not just our lives.
posted by Jane the Brown at 3:28 PM on March 22 [1 favorite]


IIRC, the 40-80% is what happens if we DON'T all stay indoors for a while.
posted by Jacqueline at 3:44 PM on March 22 [1 favorite]


Just for grins I extracted the US Covid Confirmed data into this handy spreadsheet.

I don't know what the exact mechanism would be, but I do know that epidemiological calculations include compliance estimates and I'm told they're never anywhere near 100% to start, and that they will decline (often sharply) as time passes.
posted by Tell Me No Lies at 3:52 PM on March 22


I think the idea is, 40-80% could either get it over the next three weeks, or the next six months, depending on whether we do effective social distancing. Six months is better. Three weeks, the health system breaks down.
posted by mono blanco at 3:53 PM on March 22 [20 favorites]


This essay is too long and detailed to accurately summarize, but if yours truly (who is not a doctor or medical professional) is reading it correctly, the next few weeks of isolation is to buy time for healthcare systems to shift to what is essentially a war-time footing, and begin mass manufacture of the masks, gowns, beds, ventilators, and other equipment they anticipate needing. That's Phase 1: The Hammer (aka Flattening the Curve).

But you're correct, that if we're all staying home now, we're not building up immunities and the disease could flare-up again if we resume normal life in 4-6 weeks. So Phase 2 is called "The Dance". It means slowly reintroducing activities based on 1) how costly it is to be without them and 2) how likely they are to cause an outbreak if someone who's shedding virus is there. Infections would unavoidably still happen, but at a controlled rate that stays within manageable bounds of the expanded testing-and-treating capability. And that Dance has to continue until a vaccine and/or successful treatment is confirmed, which looks like 12-18 months.
posted by The Pluto Gangsta at 3:59 PM on March 22 [28 favorites]


loveandhappiness: "My county in Florida has 12 confirmed cases."

The key word is "confirmed." Due to widespread lack of testing, there are likely many, MANY more cases circulating than the official numbers indicate. Ohio's Dr. Amy Acton estimated there may be up to 100,000 carrying the virus in her state alone.

The large-scale lockdowns are a last-ditch attempt to slam the brakes on this invisible spread before it becomes symptomatic and overwhelming, both to space out the number of cases hospitalized simultaneously and to give the healthcare system time to ramp up supplies and personnel. Depending on how large the actual caseload is, we may need to continue the lockdowns as needed for weeks or even months, until a competent testing/tracking regime like South Korea's is in place or until we develop a workable vaccine.
posted by Rhaomi at 3:59 PM on March 22 [9 favorites]


According to ”smart thermometer” data, Florida’s about to become a hotspot.
posted by liet at 5:26 PM on March 22 [4 favorites]


I would like to recommend the article that The Pluto Gangsta linked to. It is extremely informative and thorough, and also very readable and clear. The Pluto Gangsta's summary is pretty excellent (in this non-medical person's opinion) but I can't recommend the article enough.
posted by MangoNews at 5:47 PM on March 22 [1 favorite]


To pull out the testing point in the above answers, that's how we leave the house again (to my understanding - I am not a medical professional). You let people out over time, keep social distancing, but only when can you aggressively test and then isolate and trace contacts when somebody tests positive. That keeps the transmission at a low hum and treatment within our newly-increased emergency healthcare capacity, while letting some version of the economy function.

To speculate, life likely won't be "normal" - we'll need some new social norms to make this work (remote work, social distancing, masks, increased cleaning of public spaces, temperature checks at public buildings like in S Korea). In the US, we'll no doubt fight about how aggressive and how mandatory to be.
posted by troyer at 5:56 PM on March 22 [1 favorite]


It will happen slow enough for the hospitals to keep up with caring for everyone as they go into critical condition.

But of course that's never going to happen because we're biligerantly unprepared and no one really seems to understand they need to stop congregating and moving about.
posted by humboldt32 at 6:31 PM on March 22 [4 favorites]


I feel like people are misunderstanding the question that the OP has posed. They're asking: how can it be possible that 40-80% of people are STILL predicted to get COVID-19 with social distancing in place? If most people are staying inside, how can they possibly get this disease?

I have been wondering this myself.
posted by thebots at 6:42 PM on March 22 [6 favorites]


There are simple things the US and Europe could already be doing that other countries are doing. The one that jumps out to me as obvious and cheap is thermal scans in airports. Nobody with a high fever should be getting onto an airplane (or a subway). It astonishes me that that you can still board an airplane in the US with a fever.

I remember travelling for business in the weeks immediately after 9/11. There were poorly trained national guardsmen (and women) carrying automatic weapons dangerously in the airport. Fortunately nobody was hurt. Anyway my point is that it was treated as an urgent matter to increase airport security. But AFIK, we're still not even doing simple, cheap and obvious things to secure our transit hubs. Why not?
posted by sjswitzer at 6:49 PM on March 22 [1 favorite]


The way I think about (engineer not a medical professional) is that social distancing is not perfect, perhaps not even close to perfect. All it does is slow down the spread, it on its own can't prevent the spread. Essentially it lowers the probability of you catching the virus, but not to zero. You still have to go get food (or a member of your household does) and you have a non-zero chance of catching it then. So eventually given enough time many people will catch it. But that is exactly the point of social distancing, it is to slow the spread (flatten the curve) so hospitals and so on can keep up.
posted by Long Way To Go at 6:50 PM on March 22 [3 favorites]


The virus will continue to be “around” until we develop sufficient immunity to it in the population, either through infection (bad!) or a vaccine. People have to interact, and when they do, the virus spreads. You have to leave the house to go the store, for example. People have to interact to provide food, electricity, medical care, essential services. And at some point you have to interact with the people who do that, or interact with someone who interacts with the people who do that, and each interaction puts you at risk of infection.

The point of social isolation is not to keep it from spreading (it will!) but to slow the pace of spread so that it does not overwhelm hospitals and end up killing more because of a lack of resources.

The virus will spread because the isolation can’t be perfect without everyone starving to death. When we leave the house to resupply, we run the risk of infection.
posted by dis_integration at 7:13 PM on March 22 [4 favorites]


One person at the grocery store where you buy a single carton of eggs is infected but not showing symptoms. That person happens to be your cashier. They sneezed into their elbow 5 minutes before you met them, because that's what you're supposed to do. In addition to hitting the sleeve, some of the sneeze droplets also made it onto the conveyer belt.

As they ring you up, from six feet away the carton of eggs brushes their shirt sleeve and then they put the eggs on the conveyer belt. You pay with a debit card, using a bit of tissue to press the key pad. You say, "eh, I don't need a plastic bag" and you take the eggs off the conveyer belt to place them in your canvas tote. You get the eggs settled, and you head out the door. As you exit, you catch a gust of wind and it makes your eyes water. Without realizing it, you reflexively wipe a tear off your eye with the hand that was shuffling the eggs.

Congratulations, you've just perfectly transferred a tiny bit of sneeze from the egg carton to your eyeball.

In five days you will begin sneezing and you will tell yourself, "but all I did was go buy eggs, I didn't even get close to anyone, and I certainly didn't touch anyone. This can't be corona virus."

The person who was your cashier never notices any symptoms more severe than sneezing, and if they had, they would have just taken a fever reducer. They need the grocery store job and can't even afford time off to recover.

Since you are sure you don't have corona virus, you take a walk to get some fresh air and think nothing of it when you sneeze while taking a rest on a park bench. Five minutes later, a toddler toddles over to the bench and the mom says "honey, remember to stay back" and you say, "It's fine, I was just getting up." You walk away and the toddler hangs all over the bench. Mom is frustrated but thinks, "Well, it's not like this bench got sneezed on or anything."

The toddler proceeds to infect an entire family while remaining asymptomatic.

Everyone followed the rules.
posted by bilabial at 7:23 PM on March 22 [22 favorites]


They're asking: how can it be possible that 40-80% of people are STILL predicted to get COVID-19 with social distancing in place? If most people are staying inside, how can they possibly get this disease?

It’s because lockdown and extreme social distancing isn’t sustainable, probably 4 to 6 weeks at the most is all that will be possible. We’re looking at 30% unemployment rates. If the lockdown continues, there will be literal riots.

The essay linked above (“The Hammer and the Dance”) gives a good overview, but it may be too optimistic. Basically governments in charge had the choice of either (1) hundreds of thousands of deaths, potentially millions, in the short term, or (2) halt the economy to lock everything down, resulting in either (a) hundreds of thousands of deaths in the next six months, but hopefully not millions (this is “flattening the curve,” still pretty bleak) or (b) only thousands of deaths if the additional time allows for enough mobilization to test, monitor, track outbreaks, and supply medical workers. The danger is that if we don’t mobilize enough, there still could still be hundreds of thousands of deaths, only now we’ve also wrecked the economy and are looking at a depression that could cause a decade of pain.

At this point, the economic depression looks very likely, so we have to hope the the short term lockdown works and we can stay on top of future outbreaks so we don’t get the worst of both worlds. (To be fair, the scientists and epidemiologists rightly advocated for lockdowns to reduce the death toll. There was relatively little discussion of weighing the risks of likely economic depression (not the scientists’ job to care about) against what is still only a potential to stop the progress of the epidemic. There could be an argument that allowing the healthcare system to get swamped and the catastrophic death toll that would bring would be better in the long run than total economic failure, but there wasn’t much time to consider all the hypotheticals and anyway it’s too late for that now.)

In conclusion: the lockdown has to work because all bets are on buying enough time to control the disease, but it’s still not a guaranteed result.
posted by stopgap at 7:55 PM on March 22 [4 favorites]


If 40-80% of population will contract SARS-CoV-2 when and how will this happen if we are isolating now?

OK, as far as I can tell this 40-80% number seems to be mostly originating from interviews with Harvard epidemiology professor Marc Lipsitch - Here's one from The Atlantic.

If I'm reading him right, he thinks that we will reach that high "percent infected" because of a combination of 1) COVID-19 is highly transmissible (especially compared to other recent pandemics, like SARS or "bird flu"); 2) he feels it is very likely that many infected people will have few or no symptoms and 3) the sort of social isolation required to really halt the spread of the virus is simply not possible long term.

Note that Lipsitch says 40-80% over the course of a year, not like in the next three weeks.

So in his model, he's looking at something like bilabial's scenario happening again and again and again all over the world over the next year - but only a small precent of those infected will get sick enough to even seek medical treatment, much less die from it.

FTA: "Lipsitch is far from alone in his belief that this virus will continue to spread widely. The emerging consensus among epidemiologists is that the most likely outcome of this outbreak is a new seasonal disease—a fifth “endemic” coronavirus. With the other four, people are not known to develop long-lasting immunity. If this one follows suit, and if the disease continues to be as severe as it is now, “cold and flu season” could become “cold and flu and COVID-19 season.”

So that's the when & how - we can't isolate forever, over the course of the next year (at least) people will get infected but basically not notice and will in turn infect others, who will themselves not notice.
posted by soundguy99 at 8:36 PM on March 22 [2 favorites]


Although our health officials haven't laid out the underlying strategy in explicit terms, I suspect it goes something like this:

The virus is out and infecting humans. We are all probably going to be exposed to it at some point before there are vaccines to provide some immunity. Many of us will become infected. Most of us will experience a mild disease. A small percentage will experience a more severe disease and need to be hospitalized in order to survive the disease. A smaller number will die from the disease.

We can't shelter at home until there is a vaccine. The steps being taken now will "flatten the curve" so that the small percentage that needs hospitalization and medical intervention can all receive it, maybe.

In the future we will be better prepared when the really lethal pandemic strikes (hopefully).
posted by mygoditsbob at 9:09 PM on March 22 [1 favorite]


First, thank you for sheltering in place and heeding the call to isolate; this will help to slow the speed of transmission in your community, hopefully prevent the health care system from becoming overwhelmed and allow for the necessary care of those who do get sick (with anything, not just COVID-19).

The answer to your question hinges on the confirmed cases versus cases that are undetected, which are related to (under)testing, both mentioned above. Add to this transmission of COVID-19 by people who are asymptomatic.

A town in Italy where the first Italian death occurred tested their entire population (~3000). At the time of the first symptomatic case they found 89 additional cases through testing, most asymptomatic.

From the article:
"We made an interesting finding: at the time the first symptomatic case was diagnosed, a significant proportion of the population, about 3%, had already been infected – yet most of them were completely asymptomatic. Our study established a valuable principle: testing of all citizens, whether or not they have symptoms, provides a way to control this pandemic."

It's written up here.
posted by lulu68 at 9:39 PM on March 22 [4 favorites]


40-80% getting infected is not the same as 40-80% needing hospitalization, if that helps to clarify anything.
posted by affectionateborg at 4:11 AM on March 23 [3 favorites]


I'm having a hard time understanding how so many will contract coronavirus when we are distancing and staying indoors. I am aware that not all are distancing but a great majority are it seems.

Human error and blind spots. I'd bet that if you followed some of the people who swear up and down that they're absolutely social-distancing, you'd find them sitting close by someone in a park when they take their kids to the playground, or you'd see people pass close to them in a supermarket unawares. Or maybe one of the deliverymen who brings them food is infected and infects them that way.

Social distancing was meant to slow the spread, not stop it entirely. I mean, if it does stop it entirely then yay, but that's not likely - the only way to completely eliminate the spread would be to lock everyone inside their houses for 3 weeks, and that would cause even more chaos. There is some unavoidable risk we take if we go outside, or if people come to our doors.
posted by EmpressCallipygos at 7:24 AM on March 23




Human error and blind spots. I'd bet that if you followed some of the people who swear up and down that they're absolutely social-distancing, you'd find them sitting close by someone in a park when they take their kids to the playground...

Not to single you out, Empress Callipygos, but that's a blind spot right there. Our city shut down playgrounds because parents and grandparents were allowing kids to touch and climb all over the potentially contaminated playground structures, and obviously the kids were not staying 6 feet apart even if the adults were (which they weren't). And anyone who thinks kids can be trusted not to touch their faces or put their fingers in their mouths or up their noses, well...

With reports that the virus can survive on hard surfaces for quite some time, one infected kid could infect tens or even hundreds of other kids, and then each of those kids could go on and infect their siblings, parents, grandparents, babysitters, etc. This is even more probable due to the fact that children are less likely to show severe symptoms, and many are completely asymptomatic.

So yes, blind spots. Even well-meaning people can misunderstand or choose a looser interpretation of social distancing guidelines. Many people are not particularly fussed about following the guidelines at all, and are actively providing the virus with prime opportunities to spread. And given it only takes one slip to start a new chain of exponentially increasing infections, there you go. Google "patient 31" in South Korea to see how much damage just one person can wreak due to ignorance, and it's easy to see how projected rates of infection can be so high.
posted by keep it under cover at 4:55 PM on March 23


My understanding (not in any way an epidemiologist) is that the 40-70% number is really related to the R0 of COVID-19. The R0 is the basic reproduction number; in a population without immunity, how many people will an infected person go on to infect. So an R0 if 2 means that each infected person (on average -- this is all on average) infects two more; if it's 4 then each infected person infects 4 more. COVID-19 is thought to have an R0 somewhere around 2.4. If the R0 is greater than one, then the disease spreads in the population, and the higher the number, the faster the disease spreads.

There is a phase where a new disease can be contained; if everyone with the disease is quarantined, then the disease won't spread. For a number of reasons (increased global connectivity, most importantly that people are contagious before they show symptoms), this is essentially impossible now. A number of folks above have shown how it can be transmitted even though we have restricted our interactions.

The other thing the basic reproduction number can tell us is what a disease looks like when it is endemic - that is, it's approaching a steady state. Since (in general, and hopefully for COVID-19) people get immunity when they have had a disease, a disease starts limiting itself in the population. The inverse of the R0 is the proportion of the population without a disease when it's endemic.

If, for example, the R0 is 3, then each person infects three others. But if 33% of the population has already had the disease, then one of those people, statistically speaking, already have had the disease and won't get infected. So the person will only spread it to two. Eventually, 66.6% of the population will have the disease, and only one of the three people infected will be vulnerable to it and the number of people with the disease will be constant; one in and one out. This is herd immunity. This is also why measles has been a problem thanks to the antivax crowd; it has a very high R0 (12-14 per Wikipedia), which means that it starts spreading when immunization rates drop below 92% or so.

So if the R0 of COVID-19 is 2.4, that represents a steady state of around 58% of people with it. (If it's 1.9, then the steady state is around 47%, and if it's at 4, the steady state is around 75%. Most estimates for COVID-19 are in this range.) Since we can't put the toothpaste back in the tube, eventually, there's going to be somewhere in the 40-70% range with it. Some of them may be people who had it but didn't realize because the symptoms were very mild. Some will be people who have had it an recovered. Eventually, some of them will be people who have the antibodies because they have been vaccinated against it. How we get there -- and most importantly, if we can get there while maintaining enough hospital capacity so that all serious cases are treated -- is what all the response is about.
posted by Homeboy Trouble at 5:05 PM on March 23 [3 favorites]


Thank you all. Stay healthy. I appreciate all of the answers.
posted by loveandhappiness at 9:34 AM on March 25


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