Does wearing a mask protect you from coronavirus?

There was some confusion early on in this crisis about masks.  The WHO originally said that "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 prevent them from infection with respiratory viruses, including COVID-19.", but has since shifted to a position that a mask alone is not enough.


The US Surgeon General tweeted on Feb 29 "Seriously people- STOP BUYING MASKS! They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can't get them to care for sick patients, it puts them and our communities at risk! https://t.co/UxZRwxxKL9." 

I don't know what that link (which goes to the CDC) originally said, but now it recommends wearing a mask ("Everyone should wear a cloth face cover when they have to go out in public, for example to the grocery store or to pick up other necessities.").  The CDC webpage now even has a video of that same Surgeon General making a mask from an old T-shirt and two rubber bands.

So right now the CDC is encouraging mask use, and the WHO is at least no longer discouraging it.

I've posted a blog post in which I describe how I feel safe going out in public wearing my N95 mask.  I've been posting links on FB along the way, as research came out, FB is not great for finding old posts, so here they are, for those who want them all in one place.


From March 20th
https://www.facebook.com/jennifer.gruenke.5/posts/612546845366

The main study I was looking at was this 2008 study of the filtration capacity of homemade masks.  The best was one made out of a tea towel. In this image, the different colors are different people wearing the mask, the X-axis along the bottom is time, and the Y-axis on the left is a protection factor for the person wearing the mask.  A protection factor of 3, for example, only one-third of the particles make it into the mask.  That's not nearly as good as an N95 mask or a surgical mask, but it's much better than nothing.

I also mentioned this study, which showed that masks protect health care workers from bacterial infections. Not the same as viruses, but still the same general idea.

From March 31https://www.facebook.com/jennifer.gruenke.5/posts/613095540776

This is a study modeling the effect of masks in Wuhan, China.  I'm not crazy about models, but they do cite a meta-analysis, that show a strong reduction in infections in multiple studies of health care workers exposed to various pathogens.

From April 5https://www.facebook.com/jennifer.gruenke.5/posts/613347775296

This is not an official academic source, but it is reporting on filtration by different kinds of fabrics, for those making their own.  The best homemade mask filtered 79% of virus-sized particles.  They said "The best masks were constructed of two layers of heavyweight "quilters cotton" with a thread count of at least 180, and had thicker and tighter weave."

From April 22https://www.facebook.com/jennifer.gruenke.5/posts/614724386556

This was a news report as well, but there is an academic version here.  Researchers put a nylon stocking over a homemade cloth face mask, in order to improve fit to the face, and eliminate air coming in from the edges.  They found that "Use of a nylon stocking overlayer brought the particle filtration efficiency for five of the ten fabric masks above the 3M surgical mask baseline."

From April 23https://www.facebook.com/jennifer.gruenke.5/posts/614884450786

This is a study of outgoing virus, that is, how much you spread to other people with and without a mask. They were using surgical-type masks and found that they blocked coronaviruses (the cold-type; this was before covid came along)

The image below is new, but this math person has made a model for how safe it is to go outside with and without a mask. I'm not generally a big model person, but she at least gives you the spreadsheet so you can download it and change her assumptions as you wish.  And even if it's off by a factor of ten or a hundred, the risk of catching the virus outside your home while wearing a mask and being mindful of hand hygiene is really small.https://medium.com/swlh/so-youre-going-outside-a-physics-based-coronavirus-infection-risk-estimator-for-leaving-the-house-d7dcae2746c0

I definitely remember more studies, for example one in China where the health care workers in the Covid-19 ward were given the N95 masks, and those in other wards had to go without.  Zero health care workers with the masks caught Covid, whereas there were multiple cases among the workers without the masks.  But I can't find the link.

The current general attitude of one nerd node of trust towards the coronavirus

I’ve been searching daily for interesting articles in the primary literature and posting them on FB with short summaries, but I haven’t really given much of my personal sense of the current gravity of the situation.  When I started grad school, we were all put in a room and taught how to read a scientific paper.  You should focus on the methods (what the researchers did) and the results (what they saw happen), but come up with your own conclusions before reading the discussion section, where the authors give their conclusions and interpretation of the data.  In fact, you might even consider skipping the discussion section altogether.  So my instinct is to show people data and let them draw their own conclusions.  But sometimes discussion sections can be really helpful.  The authors have more experience with their system, and may well have thought of something I haven’t. So while I still like the data-focused approach, I can see the value of a periodic “discussion section” to my blog / FB wall to give people a sense of what I think the data mean.

I first became aware that there was a coronavirus outbreak in China shortly after Christmas.  The CDC website had a page on it, and I was looking at their viral surveillance section to try to figure out what the crud that was going around was caused by (that disease was clearly not covid.  It didn’t kill enough people).  At that point, I was thinking of this new coronavirus as another SARS or MERS -- sad in that it was killing people far away, but unlikely to spread through the whole world. But by early March it was clearly starting to spread, and by March 11, it was declared a pandemic, which means that it was spreading quickly through many different countries.  The thing that apparently makes this virus more prone to becoming a pandemic than SARS or MERS is that it can be spread by people with no symptoms at all.  With SARS, you could take someone’s temperature before they got on a plane and have a pretty good idea whether or not they were shedding virus.  But this new virus is being spread by people in the 5-day incubation period, and by some people who never have symptoms. I took that as a sign that this could be "the big one," which I always assumed would be flu, but life is full of surprises. 

By March 15^th, I was wearing a mask when I went out in public.  I was the only one. I was sanitizing my hands with alcohol, and wiping down all the packages that I brought into my house.  I was avoiding going out as much as possible.  I’m not a paranoid person, and definitely not a germophobe.  I knew that as a healthy middle-aged person, I was very unlikely to die of the virus, and because I work alone at home, I’m unlikely to pass it to anyone else if I did catch it.  But I don’t really have health insurance.  I have a health sharing plan with a very high deductible.  And I know our broken health care system could result in medical bills that might not be covered and could ruin me financially. People who land in the hospital with covid stay there for 1-3 weeks.  That is not a small medical expense.  I had planned to move to France in December of this year, and France has an excellent and inexpensive health care system.  My plan was to not get sick or injured before then.  I’m still not entirely sure what my chances of being hospitalized would be if I caught the virus.  But I don’t think the CDC estimates of 20% are crazy.  Beyond the cost, there are also many people who survive but have a long road to recovery.  People are having strokes and heart attacks because of the virus.  Being on a respirator for weeks can permanently damage your lungs.  So I am highly motivated to avoid catching this virus.

I’ve known since the beginning that the quarantine by itself was not going to prevent infections and save lives.  What the quarantine gives us is time to study the situation and figure out some way to deal with it.  It doesn’t look like we’ve come up with a wonder drug, and we still don’t know why some areas are harder hit than others.  But there has been a lot of progress toward a vaccine, and one group in the UK has announced that they expect to have their first million doses available by the fall, and they will know for sure if they’re on the right track by June.  At this point, I’m confident that there will be a vaccine that works well enough to stop the virus, and once we’ve gotten it and waited the six weeks (ish) it takes for it to activate the immune system, we can get back to normal.

In the meantime, we have also learned that masks work really well in preventing infections.  Back in mid-March, I was wearing my N95 mask, but I wasn’t entirely confident that it would protect me, and now I am.  They’re not comfortable, but they work. If masks were 100% effective, we would need about 60% of people to wear them to prevent exponential growth of the virus. I would link to all the studies here, but I think masks need their own post, so I'll link to it once I'm done. Update: link here.

Another happy discovery is that sunlight kills the virus within minutes.  So in the time it takes me to roll my cart full of groceries to my car, unload them into the car, and put the cart where it belongs, I’m exposed to enough sunlight that I’m not worried about virus clinging to my clothes or hair and coming home with me.  I still alcohol my hands, because I can imagine that my palms don’t get enough sun to kill the virus, and hands are a major source of transmission of viruses in general.  But I’m not worried that I’ve contaminated myself by going to the grocery store. 

If you look at various studies that track R0, you see a pattern happening over and over again.  The R0 is high at first, for example this study estimates 4.5, then it comes down to the 2-3 range.  This suggests to me that a big part of transmission is the sort of thing that was easy to change.  People were shaking hands with someone who probably didn’t wash their hands after using the bathroom, and then rubbing their eyes.  Once the first wave of sick people showed up, everyone started being more careful, even as they went about their normal lives of school and work. This helped a lot. By March 15th, which is the point where I was aware that I needed to be careful, the R0 for most of the US was already down to 1.5 or so. Then we went into quarantine, and the R0 went down even more.  You can see graphs of R0 over time for US states here. The large majority of states are currently in negative growth of the virus. (Side note: this website uses the term Rt instead of R0.  There seems to be disagreement between epidemiologists about whether R0 should be reserved for the "background" level of spread without taking measures like we are now.  The thing is, it's almost impossible to define what behavior counts as background, so I just use R0 to mean whatever the reproduction rate of the virus is at a given point.)  

So the question now is, how much can we open up while still keeping the spread rate negative?  We are clearly being more cautious now in TN than before the quarantine began.  I see about three-quarters of people wearing masks in the grocery store, and before the quarantine, it was none.

We don’t really know at this point whether or not eating in a restaurant with six feet of space between tables will lead mass outbreaks, but apparently we Tennesseans (and several other states) are going to do that experiment.  There was one instance of spread in a restaurant in China, apparently due to air flow over much longer distances.  I most definitely will not be eating out in the near future.  I’m hoping that the people who do are young and have good health insurance. 

I was encouraged by this study, which found that voting in Wisconsin apparently did not lead to a big spike in cases.  We don’t know how many of the voters were wearing masks, but probably at least some.  So this isn’t an indication of what will happen with restaurants. But it is probably more exposure to other people than one would experience going to a store, given that people were waiting in line to vote for hours.

So my prediction for Tennessee is that there will be an increase in spread now that restaurants are allowed to open, but I don’t think it will be the high rate of spread seen in New York at the very beginning, or even what we had at the beginning of the outbreak here, because most public spaces are conducive to mask-wearing, and it appears that most people are now wearing masks in them. I just don’t know if it will be higher than R0 = 1, which would give increasing numbers of new cases over time.   Again, I’m hoping that the older and at-risk people stay home until we see the results of the not-very-scientific experiment.  

If you are someone who is highly motivated not to catch the virus, you can protect yourself by wearing a mask, by sanitizing your hands and things you bring into your house, and by not touching your face until you get back home.  If you want to go the extra mile, you can change clothes as soon as you come home.  It will be an annoyance, but your risk of catching the virus will be dramatically reduced.  

Sweden, the US, and Covid-19

Sweden has been somewhat slower than other countries to implement social distancing, although looking into it for this post has revealed to me that the difference between Sweden and the US are not as great as is generally believed.

General recommendations and awareness to do social distancing appear to have been happening at more or less the same time in both countries, although that is hard to pin down exactly, because the US is huge and recommendations varied across the states.

In the US, the US federal government officially recommended closing schools and avoiding gatherings of more than 10 people on March 16th. On the same day, the Swedish government recommended that people over 70 should stay home, and that employers should consider letting their employees work from home. At this point, Sweden shut down universities and schools for older kids. But schools for young children remain open, even now. The argument there is that healthcare workers need somewhere for their young kids to go while they are working. Older kids can be home alone and do school online. So there is one real difference. In the US, elementary-aged kids have been out of school since about 3/16, whereas in Sweden they are still in school.

On 3/24, Sweden placed restrictions on restaurants, in which eating at crowded bars was prohibited, but take-out and socially-distanced eat-in tables were allowed. In the US, we shut down all eat-in tables around 3/16. So that's another real difference.

Sweden eventually banned (as opposed to just a recommendation) all gatherings over 50 people (on 3/27). The March 16th recommendation by the White House recommended limiting gatherings to 10. That's another difference.

So far, those are only differences in recommendations and laws, which are not the same as people actually socially distancing. If we look at Google’s cellphone tracking data, the US has a 38% decrease (as of 4/26) in tracking people to workplaces.  In Sweden it’s a 36% decrease, probably not a statistically significant difference. The US has a 14% increase in residential locations, whereas in Sweden it’s 11%. The only major difference in location data for the two countries is for parks (which includes public spaces like beaches).  People in these spaces has decreased 16% in the US, but *increased* 56% in Sweden.  I don’t know enough about public spaces in Sweden (or much of the US, for that matter) to say how difficult it would be to maintain distance there.  The other difference is that retail movement in the US went down 45% and stayed there.  In Sweden it has bounced around a bit, and is now at an 18% decrease.  This gives the impression that people are genuinely spending more time in public spaces in Sweden than in the US. 

Now, if we look at the results (via Worldometer) in terms of Covid-19, the US has 166 deaths per million, whereas Sweden has 217 deaths/million.  We also need to consider testing.  Countries that test more will have more official Covid-19 deaths.  The US is at about 16k tests per million, and Sweden is at 9.3k per million. This suggests that Sweden might be missing more of their Covid deaths than is the US, which would make the difference even greater. 

If you look at the graphs of deaths per day on Worldometer, Sweden appears to be processing tests on a weekly cycle, which makes trends hard to identify.  But to my eye, it looks like the US is leveling out more than is Sweden.

It's at least possible that Sweden's strategy will have an unintended beneficial effect.  There is some evidence that you can re-awaken immunological memory to other coronaviruses to help fight this one.  The idea is that through low-level exposure over time, you will wake up the memory T-cells from prior infections.  But you could get this same benefit without the risk of people actually getting sick by giving everyone low levels of inactivated virus, perhaps by putting it into the water supply.

It's pretty clear that both the people on the left claiming that Sweden is seeing a huge spike, and those on the right claiming that Sweden has managed to avoid the negative consequences without shutting down are both wrong. Sweden is partially shut down, probably not quite as much as the US, and is seeing a moderate increase in deaths relative to the US.

Serology (antibody) studies to determine the extent of covid-19 spread

Antibodies are proteins that can recognize specific pathogens that you've been exposed to in the past.  They are produced by plasma cells, which develop from B-cells.  The first time you're exposed to a new pathogen, your immune system will sort through all its B-cells until it finds the ones that produce antibodies that will stick, at least somewhat, to some part of the pathogen.  Those B-cells then go through a process of dividing, while at the same time tailoring their antibodies to stick to the pathogen really well.  Once that process is done, some of the B-cells mature into plasma cells, which are little antibody factories, and some form memory B-cells, which can reawaken if you're exposed to the same pathogen again.  Some antibodies are found in the blood, others in various secretions, like mucus and breast milk. For SARS Cov-2, the antibodies in the mucus layer lining your respiratory and digestive tracts are probably the most relevant to preventing infection. In high enough numbers, they will physically prevent the virus from ever reaching your cells.

What this means is that there is a period of some months, sometimes over a year, after exposure to a pathogen when you can take a blood sample and find those specific antibodies.  Lack of antibodies is not really a good indication that the person doesn't have immunity, because they might have memory B-cells in reserve, and there are also memory T-cells, which are totally different ways to fight a virus.  And it's possible to have antibodies without having full protection against the pathogen.  But in general, antibodies in the blood are a good indication that sometime recently that person has been exposed to the pathogen and had an immune response to it. 

We are now getting to the point where we can screen populations in an attempt to determine how many of them have antibodies to the virus.  This doesn't necessarily mean that they had an infection.  They might have had memory B-cells to previous cold-type coronaviruses, and their immune system recognized the similar pathogen and woke up those B-cells to start making antibodies.  This is the most prominent theory of why flu viruses go away in the summer.  The idea is that during the winter, people are exposed to low levels of the flu virus, and awaken their immunological memory, even without an infection, to the point where the population gets herd immunity to the flu going around that winter. 

In order to get herd immunity to covid-19, we need personal immunity in roughly 60-80% of the population. None of the populations studied so far have gotten close to that, but it's worth paying attention to these numbers.  Aside from monitoring how close we are to herd immunity, the other consequence of knowing how many people in a population have antibodies is that it *might* allow us to get a better handle on the case fatality rate, or at least on the general "danger level" of the virus in the future.  If we assume that everyone who has antibodies was actually infected, we can assume that the total cases are equal to the survivors with antibodies plus the fatalities.  Divide the fatalities into the total cases, and you'd have the case fatality rate.  But as I described above, I don't think that it's safe to assume that everyone who has antibodies was infected.  We can't even assume that they are now totally immune, although they probably have at least partial immunity.  But it does give us a reading on the overall immunological situation.

So with that introduction, here are the serology studies I know about to date:

Santa Clara County, California: 

https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v1

This is a serology study done in northern CA in early April, about 2 months after the first official case in this location. They advertised for volunteers on FB and screened blood samples for antibodies to the virus. Out of about 3300, 50 were positive. That's 1.5%, which is much higher than suggested by the official cases at the time. The authors noted that minority groups were underrepresented in their sample, and so corrected upwards.

My concern with this study is that they might have gotten a self-selected bias. That is, people who suspected that they had been infected might be more likely to answer the ad and go to the trouble of getting tested. While they did ask people whether or not they had been symptomatic, they didn't report anything about those answers. I suspect that the reviewers are going to call them on that. Their estimate of cases is high enough that it leads to the conclusion of a very low case fatality rate. That suggests that either the fatalities are dramatically under-counted, or their sample is over-representing cases.

So while it seems likely that the true number of cases is under-reported everywhere, due to the shortage of tests, I don't think that they are under-reported as much as these authors suggest.

Scotland

https://www.medrxiv.org/content/10.1101/2020.04.13.20060467v1

In this study they are screening blood donors, which excludes symptomatic people. In mid-March, there were zero blood donations with anti-SARS2 antibodies. But in late March, there were 5 out of 500 that had neutralizing antibodies, that is, antibodies able to prevent infection, and a sixth was positive for antibodies, but not necessarily neutralizing antibodies. That's 6/500 or 1.2% of the blood-donating population.

Assuming that there is a 7-day delay in testing, the number of people who had tested positive at this time was 1600. Divide that into 5.3 million, and you get 0.03%. So far more antibodies in the population than suggested by the official tests.

I think this study is better than the one in Santa Clara, CA, because they are probably avoiding self-selection by people who really want a test.  There are rumors circulating that you can get a free covid test by donating blood, but my guess is most people are not going to assume that that's the case.  It's also better to test for neutralizing antibodies, rather than just any antibodies, given that we care whether or not the antibodies present will actually prevent infection.

The really interesting thing here is that the blood was all negative on March 17th, but 1.2% positive for the samples collected between March 21-23.  It takes at least a few weeks to get a new antibody response going in a mild case, (see for example this paper) and two weeks prior to March 21-23, there were only a few official cases in Scotland.  This suggests to me that they're getting re-activation of memory B-cells from colds, which happens more quickly, not totally new immune responses from silent infections. But we don't know that for sure.

Los Angeles

http://publichealth.lacounty.gov/phcommon/public/media/mediapubhpdetail.cfm?prid=2328

This is a press release, not an academic paper.  The meat of it is found in this quote:

"Based on results of the first round of testing, the research team estimates that approximately 4.1% of the county's adult population has antibody to the virus. Adjusting this estimate for statistical margin of error implies about 2.8% to 5.6% of the county's adult population has antibody to the virus- which translates to approximately 221,000 to 442,000 adults in the county who have had the infection. That estimate is 28 to 55 times higher than the 7,994 confirmed cases of COVID-19 reported to the county by the time of the study in early April. The number of COVID-related deaths in the county has now surpassed 600."

Unlike the study in Santa Clara county, they are attempting to get a random sample of the population: "Participants were recruited via a proprietary database that is representative of the county population. The database is maintained by LRW Group, a market research firm."

It's hard to say too much with so little to go on, but this at least looks encouraging.  It's tempting to speculate that the reason CA has not been hit as hard as NY is that Californians passed around a cold-type coronavirus in the past few years and are now awakening their immunological memory.

Swiss military recruits

https://militaryhealth.bmj.com/content/jramc/early/2020/04/16/bmjmilitary-2020-001482.full.pdf

One recruit out of 140 in the whole company went on vacation, and four days later became symptomatic.  That initial case tested positive via RT-PCR, and was isolated.  55 recruits who had been in contact (direct or indirect) with that first patient were put into quarantine.  In one quarantine room, seven out of nine recruits developed symptoms.  Only one of those tested positive via RT-PCR, which brings our official positives to two.  The interesting thing here is that the second case was never in direct contact with the first case, only indirectly through a third person who never tested positive. The other interesting thing here is that only the two official positive cases developed antibodies.  None of the others, including the six who had mild symptoms, and the person who was presumed to have carried the virus from patient 1 to patient 2, developed antibodies.  It's possible that the tests (both PCR and antibodies were not sensitive enough to pick up low levels.  Or it's also possible that the transmission from patient 1 to patient 2 via the third person was just through carrying the virus on his hands.  But what we're not seeing here is young healthy people developing a robust immune response to the virus.  It appears that they're just not very susceptible to catching it, compared to the general population.