I’ll preface this whole thing with a reminder that I’m an engineer and librarian, not a biologist. I have spent months reading articles, posts, and tweet threads written by doctors, epidemiologists, and public health experts, but I am not, myself, an expert. I’ll post a version of this online and let you know if someone drops in to correct anything I’ve said here. And I’ll update you if our understanding changes again–you know how science is, especially when dealing with something like a novel virus: we keep learning new things that change our approach.
If this is all too much to read, a very short summary: the things that increase risk are proximity to other people, total amount of time with other people, lack of masks, and lack of ventilation. Being outside with a mask on and six feet of distance between you and other people who are all wearing masks: kind of best-case, especially if it’s only a short time. Being in a small space that isn’t well-ventilated for several hours with other people: real bad. (A tweet thread on this, with articles, is here.) Also, more people are sick than our governments are acknowledging or admitting.
Now, here’s a more complete summary:
OK, so. How bad a case of COVID-19 a person gets seems to depend at least partially on the amount of virus they are exposed to. A person with a properly functioning immune system can be exposed to a very small amount of the virus and not get sick at all; if it’s a small enough amount, their body just washes it away, and I don’t believe they even test positive on an antibody test later. Let’s say it takes something like 1000 viral particles (that’s a great article!), for most people, to induce illness—the jury is out about autoimmune diseases’ effects on this number, though my educated guess says “it is probably smaller,” so we have to be more careful than the average person, and of course 1000 is just an estimate. Also, it seems to be generally accepted as fact that the difference in how sick someone gets will vary greatly with their exposure, so someone exposed to 1001 virus particles is likely to get a lot less sick than someone exposed to 100,000.
The virus is spread by droplets which come out of the nose and mouth during breathing, talking, shouting, sneezing, coughing, etc. Some of those activities spread droplets further and higher into the air than others, as you’d imagine. The article I linked above suggests that coughing might release 3000 droplets, a sneeze might be 10 times that, and a single breath could vary between 50 and 5000 droplets, but they would fall more quickly and not spread as far as a cough or a sneeze. Masks will keep a lot of that contained! Maybe not all of it, especially with a homemade mask instead of an N95, but both serve to significantly decrease the number of droplets leaving a person’s airways. That’s why people who decide to go into public without masks on are assholes, with the exception of the relatively few people who literally cannot wear them. (Note: a droplet coming from someone who has a virus is likely to have more than a single virus particle in it. It seems, from the article, that a single droplet from someone with COVID-19 might contain between 5000 and 70,000 virus particles, and some of that variation has to do with where they are in the course of their illness.)
Now, the droplets with virus particles can get into your body in a number of ways. You could breathe them in–and your mask helps prevent that, of course, so it’s worth wearing your mask even if you’re pretty sure you’re not a carrier of COVID-19. The droplets could fall onto a surface, and you could touch that surface and then your own nose, mouth, eyes, or something you’re about to eat or drink. The droplets could fall on one surface, be moved by your or someone else’s hands onto another surface, and then get on your hands and into your body. And so on. Washing your hands for 20 full seconds helps us safe, because COVID-19 has a lipid outer shell: soap destroys the virus. Refusing to touch your face except immediately after washing your hands: also helpful! (The mask also helps with this; you can’t touch your nose or mouth if they’re covered.)
It does mean you need to wash your mask with soap between wearings and treat it as if the outside of it is covered in virus particles when you get it home.
This particular virus stays alive on most surfaces for an incredibly long time, which is part of why I emphasized that they can be transmitted between surfaces before they get onto your hands. There was a study that showed it can live for 4 hours on copper, 24 hours on cardboard, and 72 hours on plastic, although I don’t know that that study has been replicated. Humidity and temperature have some effect, too. Speaking practically and for myself: since nobody who delivers my mail or packages (aside from the CSA box) seems to wear masks now, I just assume nothing’s safe to touch for at least 48 hours, and I wash my hands after bringing things in and putting them in our quarantine containers.
The thing that a lot of places are doing, where they do temperature checks at the door, is helpful, but not foolproof. Something like 95% of people who will end up sick with COVID-19 will have a fever by day 11 after exposure (don’t quote me on that statistic, it’s a vague memory from March and may have changed by a few percentage points since then). However, with some coronaviruses, you’re actually giving off more viral particles per hour immediately before your symptoms kick in than you are a couple of days afterward. So, when the World Health Organization announced that the bulk of COVID-19 transmission is not, in fact, due to asymptomatic carriers, they had to put out an almost immediate clarification that they meant people who tested positive for antibodies but never developed symptoms, as opposed to people who were pre-symptomatic (no symptoms yet, but they will be developing them). I’m still pretty frustrated with them for that, because your average person (including me, the day before their announcement) doesn’t know that “pre-symptomatic” is not a subset of “asymptomatic”; anyone who only saw the first announcement and not the clarification might think the temperature checks are foolproof, and that frightens me.
Anyway, back to limiting risk. You need to stay under 1000 total viral particles (probably fewer), which isn’t a lot, granted. Now, we’re assuming you’re washing your hands (or if soap and water aren’t available, using hand sanitizer) often enough to prevent that mode of infection, so we’re mostly just worried about particles in the air. In the course of your day, your goal needs to be limiting how many viral particles get in your nose, mouth, and eyes.
Obviously, the mask helps a lot–yours and, especially, everyone else’s. Good ventilation is useful since it helps disperse droplets more quickly. There are studies showing that COVID-19 dies quickly in sunlight, so being outdoors is beneficial, beyond the whole ventilation issue. Maintaining physical distance from other people helps as long as they’re breathing normally, not coughing and sneezing (which can project particles a lot further than six feet) or talking (which projects it further than just breathing but not nearly as far as coughs/sneezes)—honestly, I wouldn’t go within 20 feet of someone who isn’t masked, nowadays: they’re showing poor judgment, and I’d just assume they are a carrier. (There are legitimate conditions that prevent mask-wearing, and children under the age of 2 are not supposed to wear them. That’s valid. It is my strongly-held belief, though, that any adult who is unable to wear a mask needs to find all possible ways to avoid being indoors in public places right now, for their own safety and the safety of others.)
If you have to go into a room with another person–someone’s office, say–you should flatly refuse if they aren’t wearing a mask when you get there, and you’ll want to limit the amount of time you’re there as much as you can.
But if you’re outside on a walk and someone briefly enters your 6′ bubble? It’s not ideal, but it’s a very small risk. It’s OK to take walks! Don’t go following someone else down the trail, because then you’re in their wake for too long, but passing someone going in the opposite direction does not put you at much risk. Being passed by a bicyclist: also not a big deal.
You definitely don’t want to sing with groups. Or talk loudly with other people who are also talking loudly. There are theories (and I think they are just theories, not something we know for sure) that inhaling deeply, like you do when singing or otherwise projecting your voice, allows virus particles to get deeper into your lungs and possibly infect you … worse? more quickly? I don’t know precisely where the science stands on that, but I’ve seen it discussed in multiple places as a distinct possibility.
Someone on Twitter pointed out that people who work in grocery stores are in a lot more danger than shoppers: they’re there for their whole shift, right? Even assuming all shoppers wear a mask, that is a LOT of potential exposure, compared to the … what? half hour? hour? that a shopper is in the store. Also, shoppers move around and can control how close they get to other people, where store employees cannot, so much. To be clear: I’m not suggesting that you go into stores. Curbside is free at most stores, and it keeps everyone safer, including store employees! I shared that mostly so you understand why essential workers have been so afraid through all of this.
Anyway, having done a lot of reading, I feel very safe doing curbside, even though my car doesn’t have a separate trunk compartment. I wear a mask, which keeps the person doing the delivery safe. I tend to have the fan or air conditioner on, which pushes air past me and out the back (though, to date, everyone doing curbside has also had a mask on, so this is a minor detail—between my mask and theirs, combined with the short time involved, the direction of airflow is probably not a big deal). The car is roughly six feet long. And the duration of the encounter is very short. It’s not zero risk, for them or for me, but it’s very low risk. Less, certainly, than my wandering around a store and standing next to the cashier (even with plexiglass) for the significantly longer time it takes to ring up and bag groceries.
In contrast, classrooms are darn near the worst-case scenario. My school is switching to 3-hour blocks for in-person courses, to keep students from having to come to campus as often, which seems good on the surface. They’re shrinking sections so that people can stay six feet apart, which is a positive step, if you take “there must be in-person classes” as a given. Staff and faculty are required to wear masks; it’s unclear whether they are requiring or merely encouraging masks for students, but if it’s the latter, nobody should agree to teach in-person. Unless the school installs sound amplification equipment, the professor and anyone else who needs to talk will be doing so at a loud volume, which disperses droplets further than talking in a quiet voice; also, to project their voice, a professor will have to breathe deeply, possibly putting themself at more risk. Classrooms are notoriously under-ventilated, and people will be trapped together for three hours, now. As for the rest of campus, our faculty share small offices, and we (humanity at large, not just my college) don’t know how big a risk restrooms are—ours have very narrow entrance/exit areas, though, so even if flushing turns out not to spray live viral particles into the air, I’d rate ours on the higher end of the risk spectrum. The library on my campus has a narrow entrance/exit, too, and there’s no good way to sanitize books between users. Basically, reopening campus is going to be a nightmare, and I am worried about my colleagues who are agreeing to go back and about our students. Our Provost put in writing that nobody would be required to teach face-to-face in the fall, so at least they’re being cool about part of it. (I hope the librarians and other employees aren’t forced into the building either!)
I mentioned that more people are sick than we know about. That’s true, and it doesn’t seem to be something anyone in government is taking into account, at all. There are a number of different tests being administered in the US, with varying (largely unpublished) levels of sensitivity (meaning they give false negatives at varying and largely unknown rates); on top of that there have been delays in processing (which make the test less useful), combined with improper test procedure (not sticking the swab far enough into the nasal passage to get a proper sample), combined with the disease moving from the upper to the lower respiratory tract several days after onset of symptoms (so a nasal swab won’t catch it, anyway). There are definitely people out there who have tested negative despite having COVID-19, and the official statistics ignore their existence.
Since I recently ran these numbers for someone in a professional capacity, I’ll use Pennsylvania as an example of what this looks like at scale: It’s generally accepted that COVID-19 has an infection fatality rate of less than 2%. (I just found a paper that quoted 1.04% globally.) Using last week’s numbers, if there had really only been 76,000-some cases in Pennsylvania, and more than 5,900 had died, that would imply that PA’s infection fatality rate was something like 7.7%. There’s no way that’s true, when our hospitals never reached capacity; it’s much more likely that there have actually been at least 295,000 cases in Pennsylvania, using the 2% infection fatality rate number. (It would be even more if we assumed 1.04%.) That is, frankly, terrifying. My governor is making decisions based on the 76,000 number, not on the 295,000 number. I bet yours is doing something similar.
Now, I left the “actually, COVID-19 is terrifying” information out of this message. I’m willing to tell you all about how it might affect the brain, how children are coming down with a secondary infection which makes “it’s not dangerous for children” a very dangerous lie, about how the lungs are affected, about how the heart and kidneys and liver are apparently also affected in some cases, and so on. I can talk about previously healthy 20-somethings who suffered strokes after recovery. I can, as someone on Twitter suggested, Google “COVID lung transplant” and let you know what I find. I can go on to talk about how, even in mild cases where someone recovers fully, it takes over a month to get better. But if you’re prepared to just believe me that it’s a very dangerous disease, even for people without risk factors making it more so, I’m honestly thrilled not to have to summarize so much gory stuff. If you want to know it, though, I’m willing to write it up.