SARS CoV-2 coronavirus / Covid-19 (No tin foil hat silliness please)

Pogue Mahone

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So when are the people living in Europe going to stop wearing masks? I presume never from some of the posts here. Or are you waiting for a booster vaccine?
Presumably when the number of cases go down. And we aren’t constantly hearing about friends and family catching covid. It’s fecking everywhere now so understandable if there’s still a lot of nervousness. But the current surge will definitely end. Mainly through vaccine, partly through exposure to the virus. It will end though. It has to.
 

Balljy

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I wouldn't mind if mask wearing is here to stay. It's been pretty normal in Japan for around 100 years since the influenza pandemic and then SARS in the early 2000's. Other Asian countries wear them as a matter of course. They kind of make sense on crowded trains and buses regardless of the pandemic.

I'm doubtful they'll stay long term in Europe mind.
 

Wibble

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Wearing a mask when you have even a slight sniffle should become the norm as it reduces the spread of all airborne respiratory viruses.
 

Pogue Mahone

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Thanks for that, I should have checked back.
I was weirdly thinking about this overnight. Half awake, half asleep. Might as well brain dump. If we assume Israel has a population of ten million (near enough) they’ve fully vaccinated approximately 80% of their population. Which leaves two million un-vaccinated. We know vaccines aren’t 100% effective at preventing transmission. So let’s assume one million of the eight million vaccinated will catch covid when exposed (although it probably won’t make them very sick). Three million people is a very large number!

Their highest number of cases per day in this surge is approx 10k. If this was to happen every day from now on, this could continue for ten months before everyone who can catch covid does catch covid.

Obviously this won’t happen. Not everyone that can catch covid will catch covid. And a lot of un-vaccinated people are protected from prior exposure. The daily cases will probably get a bit higher before coming down again. The only upside of delta is that the surge seems to end a bit quicker than previous variants.

Anyway, hope this keeps Israel’s case numbers in perspective. It helped me get back to sleep anyway!
 

rpitroda

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I think in the UK now, people have effectively stopped sensibilities like wearing masks. Where I am, people were actually really good with the rules - at least in places like supermarkets. It would be rare to see someone without a mask when it was required. Now, I’d say people still wear them but must be below the 50% point. Which makes me wonder, in many other places (like other nearby places where mask wearing was probably hovering near 50% before the rules changed anyway), I can imagine that it’s back to BAU.

200+ deaths though, still shocks me. At our peak we were at, what, 1k+. So we are at about 20% of that. What worries me though is that when we had those deaths before, we were unvaccinated. Give we have a very good vaccination rate, and given 94% of people have antibodies (I know antibodies aren’t alone a factor in determining how severely one will get ill in future if they catch COVID but I’m not any kind of expert!), 200+ deaths seems pretty high to me. Even 100+ seems high in these circumstances, if you factor in the bank holiday catch up.

Can’t quite get my head around the figures and if they’re as we might have expected or if they’re showing something more concerning.
 

Mihai

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I'm in the UK at the moment, posting from a 6pm Manchester - London train. I'm the only one in the carriage wearing a mask, and it was the same coming up the other day. Feels quite uncomfortable and I'm looking forward to getting back to Italy where its infinitely more sensible.
The only places I've noticed a relatively high number of people wearing masks is the big supermarkets.
 

jojojo

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200+ deaths though, still shocks me. At our peak we were at, what, 1k+. So we are at about 20% of that. What worries me though is that when we had those deaths before, we were unvaccinated. Give we have a very good vaccination rate, and given 94% of people have antibodies (I know antibodies aren’t alone a factor in determining how severely one will get ill in future if they catch COVID but I’m not any kind of expert!), 200+ deaths seems pretty high to me. Even 100+ seems high in these circumstances, if you factor in the bank holiday catch up.

Can’t quite get my head around the figures and if they’re as we might have expected or if they’re showing something more concerning.
Single day figures aren't very useful, they jump around as local reporting varies. The 7 day rolling figure is around 100/day at the moment. High, and horrible of course, but certainly within what was expected after things reopened.

The number of people in hospital at about 7000 currently is also around the lower end of the models the government was using. Not great for the NHS staff or for patients waiting for other medical problems to be treated, but not outside what was expected.

The case rates are high, around 30k/day. When we were up there pre-vaccine we were seeing death rates of 1000+/day, hospitals overwhelmed. Research from the UK and elsewhere suggests that Delta (to the unvaxxed) may be more deadly than Alpha was - which could have made it even worse.

Basically we're getting along, more people are getting sick than anyone wants, but it's playing out roughly as the numbers for vaccines and for prior infections said it would. People aren't really back to business as usual, but we're close.

If things take a turn for the worse in the winter (as respiratory viruses usually do) then we might have to do more. Right now, the best things any of us can is get vaccinated, wear masks on public transport etc, get tested and stay home if we've got any symptoms and stay away from granny if we've spent the week at a festival...
 

Penna

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I just went to a building supplies place here in Italy, and the lady didn't have a mask on as there were no customers. She saw me, clamped her hand over her mouth and ran off to get a mask. We were virtually in the open air.

People are still taking it seriously!
 

Stack

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I was weirdly thinking about this overnight. Half awake, half asleep. Might as well brain dump. If we assume Israel has a population of ten million (near enough) they’ve fully vaccinated approximately 80% of their population. Which leaves two million un-vaccinated. We know vaccines aren’t 100% effective at preventing transmission. So let’s assume one million of the eight million vaccinated will catch covid when exposed (although it probably won’t make them very sick). Three million people is a very large number!

Their highest number of cases per day in this surge is approx 10k. If this was to happen every day from now on, this could continue for ten months before everyone who can catch covid does catch covid.

Obviously this won’t happen. Not everyone that can catch covid will catch covid. And a lot of un-vaccinated people are protected from prior exposure. The daily cases will probably get a bit higher before coming down again. The only upside of delta is that the surge seems to end a bit quicker than previous variants.

Anyway, hope this keeps Israel’s case numbers in perspective. It helped me get back to sleep anyway!
Thanks for that. A positive point you made for me there was the delta surge seemingly ending quicker. I think Im trying to work out how it all works out for us in NZ after xmas when our vaccinations are up at a decent level and we start to ease restrictions around incoming people. I have no doubt it will hit us hard even with high vaccination, its just how hard and for how long. The kicking the can down the road thing is rapidly coming to its end so trying to make sense of how the rest of the world is dealing with it gives me an idea of what we have to do to catch up.
 

Pogue Mahone

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Thanks for that. A positive point you made for me there was the delta surge seemingly ending quicker. I think Im trying to work out how it all works out for us in NZ after xmas when our vaccinations are up at a decent level and we start to ease restrictions around incoming people. I have no doubt it will hit us hard even with high vaccination, its just how hard and for how long. The kicking the can down the road thing is rapidly coming to its end so trying to make sense of how the rest of the world is dealing with it gives me an idea of what we have to do to catch up.
Yeah I can see where you’re coming from. Very tough times ahead for NZ, I suspect. The big difference between NZ and countries like UK and Israel is the lack of any baseline immunity from prior exposure. Apparently 94% of the UK population show evidence of exposure to covid during serological testing. So even the millions of un-vaccinated people have some degree of protection. That’s most likely why their delta wave didn’t kick off as badly as, say, India.
 

Pogue Mahone

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Single day figures aren't very useful, they jump around as local reporting varies. The 7 day rolling figure is around 100/day at the moment. High, and horrible of course, but certainly within what was expected after things reopened.

The number of people in hospital at about 7000 currently is also around the lower end of the models the government was using. Not great for the NHS staff or for patients waiting for other medical problems to be treated, but not outside what was expected.

The case rates are high, around 30k/day. When we were up there pre-vaccine we were seeing death rates of 1000+/day, hospitals overwhelmed. Research from the UK and elsewhere suggests that Delta (to the unvaxxed) may be more deadly than Alpha was - which could have made it even worse.

Basically we're getting along, more people are getting sick than anyone wants, but it's playing out roughly as the numbers for vaccines and for prior infections said it would. People aren't really back to business as usual, but we're close.

If things take a turn for the worse in the winter (as respiratory viruses usually do) then we might have to do more. Right now, the best things any of us can is get vaccinated, wear masks on public transport etc, get tested and stay home if we've got any symptoms and stay away from granny if we've spent the week at a festival...
Been thinking about you since the Ronaldo news broke! Haven’t seen any posts from you about it in the football forums. Presumably there’s been a bit of a spring in your step this week?
 

Stack

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Yeah I can see where you’re coming from. Very tough times ahead for NZ, I suspect. The big difference between NZ and countries like UK and Israel is the lack of any baseline immunity from prior exposure. Apparently 94% of the UK population show evidence of exposure to covid during serological testing. So even the millions of un-vaccinated people have some degree of protection. That’s most likely why their delta wave didn’t kick off as badly as, say, India.
That is such an important point and one I had only considered for the first time yesterday. No baseline immunity from prior exposure. That i think will be our weakest link. Thats the one that will bite hardest.
 

Pogue Mahone

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That is such an important point and one I had only considered for the first time yesterday. No baseline immunity from prior exposure. That i think will be our weakest link. Thats the one that will bite hardest.
Yeah it’s going to suck. I still think, on balance, the relatively normal life you’ve had in the 18 months justifies the eradication policy. Plus you’ll probably still suffer less deaths overall compared to most other countries as it’s obviously better to go through your first major wave vaccinated than naive (even if your first wave involves a more deadly/contagious variant). Such a strange situation to be in though. The rest of the world was like someone being caught in a blizzard without a jacket. New Zealand now have to deliberately walk out into a much worse blizzard. You do have a jacket but it’s going to be miserable all the same.
 

Dumbstar

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That is such an important point and one I had only considered for the first time yesterday. No baseline immunity from prior exposure. That i think will be our weakest link. Thats the one that will bite hardest.
Not to downplay NZ's attitude to handling covid (which has been great) but reopening was the very first thing I thought about as soon as you locked down over a year ago.

It's in every biological disaster movie when those that seek shelter are in the worst possible position if others survive. The Morlocks? :)
 

Stack

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Not to downplay NZ's attitude to handling covid (which has been great) but reopening was the very first thing I thought about as soon as you locked down over a year ago.

It's in every biological disaster movie when those that seek shelter are in the worst possible position if others survive. The Morlocks? :)
Ha, had long ago forgotten about The Morlocks. love it
 

jojojo

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Been thinking about you since the Ronaldo news broke! Haven’t seen any posts from you about it in the football forums. Presumably there’s been a bit of a spring in your step this week?
I'm not sure if it was the joy at him coming back to us, or the relief at him not going to City - but for sure, it was a nice break from reality :lol: I do pity the ones who'd already burned their shirts and had the tattoos erased of course.
 

Beans

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Yeah I can see where you’re coming from. Very tough times ahead for NZ, I suspect. The big difference between NZ and countries like UK and Israel is the lack of any baseline immunity from prior exposure. Apparently 94% of the UK population show evidence of exposure to covid during serological testing. So even the millions of un-vaccinated people have some degree of protection. That’s most likely why their delta wave didn’t kick off as badly as, say, India.
94% before delta had arrived? That would be pretty amazing, I was wondering how many really caught it.
 

giggs-beckham

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I think in the UK now, people have effectively stopped sensibilities like wearing masks. Where I am, people were actually really good with the rules - at least in places like supermarkets. It would be rare to see someone without a mask when it was required. Now, I’d say people still wear them but must be below the 50% point. Which makes me wonder, in many other places (like other nearby places where mask wearing was probably hovering near 50% before the rules changed anyway), I can imagine that it’s back to BAU.

200+ deaths though, still shocks me. At our peak we were at, what, 1k+. So we are at about 20% of that. What worries me though is that when we had those deaths before, we were unvaccinated. Give we have a very good vaccination rate, and given 94% of people have antibodies (I know antibodies aren’t alone a factor in determining how severely one will get ill in future if they catch COVID but I’m not any kind of expert!), 200+ deaths seems pretty high to me. Even 100+ seems high in these circumstances, if you factor in the bank holiday catch up.

Can’t quite get my head around the figures and if they’re as we might have expected or if they’re showing something more concerning.
Well the cases and deaths are on the rise. That isn't called a spike apparently, it could be called a Colin for all it matters its concerning.
 

acnumber9

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Well the cases and deaths are on the rise. That isn't called a spike apparently, it could be called a Colin for all it matters its concerning.
Cases are down over the last 7 days actually. With deaths up 0.9% over the same period.
 

0le

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Wearing a mask when you have even a slight sniffle should become the norm as it reduces the spread of all airborne respiratory viruses.
To be honest, it feels that people want this to be the case when perhaps the evidence is not as strong for it as one might think.
 

Stack

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To be honest, it feels that people want this to be the case when perhaps the evidence is not as strong for it as one might think.
I remember when this all first started down here in NZ initially the Govt advice via our Health ministry was that wearing of masks didnt have enough conclusive evidence that it made much of a difference so the advice was it was a personal choice. A month or two later they changed their mind on that advice and recommended the wearing of masks. Fortunately for us they explained this change of mind which for me gave reasons that made sense.
The first reason they explained for the initial advice that mask wearing wasnt crucial was that the evidence they had been looking at was based around Hospital use and the protocols around hygene etc there. The thinking was the general public werent as disciplined with not touching the mask and also that removal of the masks by the general public might not follow the strict hospital protocols to avoid contaminations.
The change in thinking they explained was because they felt their frame of reference was far too narrow and that the studies they had subsequently looked at showed them that even with the general publics deficiencies in how masks were worn and removed was not large enough to negate the benefits in helping reduce the possibility of spreading infection via wearing a mask.
Down here anyway wearing a mask as advised by our Health experts does have a positive impact on helping reduce infection spread.
Im inclined to follow the advice of our health professionals who have done such a great job of keeping NZs death rate and hospitalisations at an incredibly low level.
 

0le

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Huh? The evidence is overwhelming that it reduces transmission of airborne viruses.

E.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7253999/
Look at the 2nd paper of the 21 studies references in the table:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3322931/
A total of 94 case-patients and 281 matched controls were included in the final analyses.
We also used this investigation to quantify the impact of behaviors (i.e., mask wearing, handwashing) that were promoted to reduce the risk for SARS. Wearing masks outside the home in a reference period corresponding to the 2 weeks before symptom onset for cases was significantly protective against clinical SARS. Supporting the validity of this finding, there was a dose-response effect: by multivariable analysis, persons who always wore masks had a 70% lower risk of being diagnosed with clinical SARS compared with those who never wore masks, and persons with intermittent mask use had a 60% lower risk. Many persons who wore masks in the community did not use N-95 or similar highly efficient filtration devices, which have been recommended for use in the hospital setting. We sought details on the type of masks used but were unable to evaluate the protective efficacy for different mask types. We also were not able to differentiate protective efficacy for SARS-CoV versus efficacy against other pneumonia causes that met the clinical case definition.

Handwashing has been recommended to prevent SARS and other respiratory and diarrheal infections in which contact is an important mode of transmission. We found that consistently washing hands upon returning home was associated with a reduced risk for clinical SARS by univariate but not multivariate analysis. However, self-reported handwashing practices may be particularly prone to misclassification because respondents might provide the answer they believe is expected of them.
Look how absurdly biased that is. They recognise people may lie about handwashing in bold but fail to recognise this for mask wearing? I could be wrong but they also do not distinguish between masks and hand washing clearly enough here. They fail to discuss whether people were outdoors or indoors either, nor what type of environments they found themselves in.

Look at the 4th paper of the 21:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3322898/
Risk was reduced by consistent use of a surgical mask, but not significantly. Risk was lower with consistent use of a N95 mask than with consistent use of a surgical mask. We conclude that activities related to intubation increase SARS risk and use of a mask (particularly a N95 mask) is protective.
The mask that most of the general public wear (surgical masks) is not significant even in a medical situation. Again, they also only sampled a small number of cases. They also did not segregate the effect of masks from other PPE or (I assume) handwashing, as evidenced by Table 2.

I have no doubt that several other papers referenced in the paper you provided are like this.

Aside from statistical studies, at the time (2020) there were no physical CFD simulations capable of modelling accurately air-droplet flow and interactions in even the most simple of flow cases, let alone exhaled air with and without masks. This will not have changed.

The experiments in this area to describe where and how the droplets move were still confined to very limited and niche cases as well. Maybe some experiments have been carried out now, but those which show "penetration depth" of the ejected spittle in a lab setting are not particularly useful on their own.

But qualitatively, with masks such as "surgical masks" which have gaps, much of the air flow escapes in the gaps and if someone only exhales small droplets, then the air will carry most of the droplets with it. It is a similar problem with other loose fitting masks as well and obviously idiots who do not cover their noses with their masks. I have said this several times in this thread. This is why paper 4 probably found that the effect was not significant.

You may say that "people with a sniffle" should wear a mask, but actually what they should really be doing is not going out in the first place and staying at home. The only circumstances where masks can make a significant and obvious effect is where people use N95 masks (or better yet, half mask or full mask respirators) which provide an adequate seal to prevent leakage. Unfortunately, almost no one in the general public uses N95 masks as their cost makes them too expensive to use on a regular basis.

I think the problem is a bit like football in the sense that people see players names "on paper" and think the team should do well and then the reality is that for a wide range of reasons, they may not. It is a similar case for masks - under ideal circumstances they will help, but the problem is you will rarely find those ideal circumstances and the physical evidence for the alternatives is still lacking. At present we therefore rely on statistical models and surveys which, at least from the two I looked at, hardly look conclusive to me.
 

Stack

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Look at the 2nd paper of the 21 studies references in the table:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3322931/




Look how absurdly biased that is. They recognise people may lie about handwashing in bold but fail to recognise this for mask wearing? I could be wrong but they also do not distinguish between masks and hand washing clearly enough here. They fail to discuss whether people were outdoors or indoors either, nor what type of environments they found themselves in.

Look at the 4th paper of the 21:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3322898/


The mask that most of the general public wear (surgical masks) is not significant even in a medical situation. Again, they also only sampled a small number of cases. They also did not segregate the effect of masks from other PPE or (I assume) handwashing, as evidenced by Table 2.

I have no doubt that several other papers referenced in the paper you provided are like this.

Aside from statistical studies, at the time (2020) there were no physical CFD simulations capable of modelling accurately air-droplet flow and interactions in even the most simple of flow cases, let alone exhaled air with and without masks. This will not have changed.

The experiments in this area to describe where and how the droplets move were still confined to very limited and niche cases as well. Maybe some experiments have been carried out now, but those which show "penetration depth" of the ejected spittle in a lab setting are not particularly useful on their own.

But qualitatively, with masks such as "surgical masks" which have gaps, much of the air flow escapes in the gaps and if someone only exhales small droplets, then the air will carry most of the droplets with it. It is a similar problem with other loose fitting masks as well and obviously idiots who do not cover their noses with their masks. I have said this several times in this thread. This is why paper 4 probably found that the effect was not significant.

You may say that "people with a sniffle" should wear a mask, but actually what they should really be doing is not going out in the first place and staying at home. The only circumstances where masks can make a significant and obvious effect is where people use N95 masks (or better yet, half mask or full mask respirators) which provide an adequate seal to prevent leakage. Unfortunately, almost no one in the general public uses N95 masks as their cost makes them too expensive to use on a regular basis.

I think the problem is a bit like football in the sense that people see players names "on paper" and think the team should do well and then the reality is that for a wide range of reasons, they may not. It is a similar case for masks - under ideal circumstances they will help, but the problem is you will rarely find those ideal circumstances and the physical evidence for the alternatives is still lacking. At present we therefore rely on statistical models and surveys which, at least from the two I looked at, hardly look conclusive to me.
I think the problem here is you are missing an important point.
Vaccines dont stop all infections but they do help reduce infections. Social distancing doesnt stop infections but it does help reduce the ease of infectious spread. Hand washing doesnt stop all infectious spread, but it does help reduce the amount of infectious spread. Having limits on the size of social gatherings doesnt stop infectious spread but it does help reduce the amount of infectious spread.
Masks worn by the general public dont stop all infectious spread but they do help reduce the ability of the virus to spread.

Each different element helps but none of them is an answer by itself. Combine each different element and there is a combined impact on reducing infectious spread.

Reducing infectious spread is an important goal.
 

Wibble

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You may say that "people with a sniffle" should wear a mask, but actually what they should really be doing is not going out in the first place and staying at home. The only circumstances where masks can make a significant and obvious effect is where people use N95 masks (or better yet, half mask or full mask respirators) which provide an adequate seal to prevent leakage. Unfortunately, almost no one in the general public uses N95 masks as their cost makes them too expensive to use on a regular basis.
I hope people do stay at home far more when not well. I hate people bringing their illness to work just to prove how hard a worker they are. But there will be situations where people won't or can't and then masks do help a great deal as do all the other measures. The better the mask the greater the help but even poorly fitting masks are better than nothing as even the worst are a physical barrier that reduce the viral load released into the air (droplets and aerosol) and the distance droplets are sprayed.

This high speed video from the University of New South Wales shows how well masks work.

 

0le

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An LED will not be powerful enough to illuminate sufficiently well the small droplets. You need a laser for non-intrusive measurements or a counting device. Even so, that video shows coughing and sneezing and those people should be self-isolating anyway. Sure, the horizontal penetration distance of the ejected spray is altered, but you still may release droplets into the environment.

There is also another important point as well. A jet with larger momentum (as is the case with no mask), if directed to the floor, will carry all its droplets some distance towards the floor. A jet redirected vertically upwards which has lower momentum is more likely to have its droplets become entrained in the air, simply because the interaction time between the droplets and surrounding air flow (called eddies) is larger.

I have actually found a paper (July 2021) where some researchers have used PIV to quantify some of the droplet characteristics alongside olive droplets with were fixed at about one micrometer:
https://aip.scitation.org/doi/pdf/10.1063/5.0057100

Some important points (quote tags omitted):
As previously noted, a significant quantity of aerosol escapes at the bridge of the nose in Figs. 4(b) (Multimedia view) and 4(c) (Multimedia view), which highlights the importance of the fit of the mask to the face. Here, the fit of each mask is typical of appropriate usage, with the straps tightened (as outlined in Sec. II) and the built-in wire shaped to the bridge of nose. Nonetheless, aerosols escape at the perimeter of the mask due to inevitable imperfections in the mask fit, with the most significant quantity of particles escaping at the bridge of the nose. Other leakage sites include the interface of the mask edges with the cheeks and lower jaw [not captured in Figs. 4(b) (Multimedia view) and 4(c) (Multimedia view) due to laser sheet positioning]; however, these results and other supplementary measurements (not shown for brevity) confirm that leakage at the bridge of the nose far exceeds all other leakage points.

[snip]

The results in Fig. 4 illustrate that a notable amount of particles leak out at the perimeter of all masks, which is expected to result in notably lower effective filtration efficiency, compared to ideal filtration efficiency, when exhalation is considered.

[snip]

Noting the significance of both the ideal filtration characteristics (Sec. III A) and fit of a mask (Sec. III B), it is apparent that both effects must be taken into account in order to provide an accurate measure of the effectiveness of a mask in reducing the dispersion of an aerosol exhaled by an individual.

[snip]

The cloth and surgical masks perform relatively poorly with efficiencies of only 9.8% and 12.4%, respectively, due to both low material filtration efficiency and significantly higher amounts of leakages around the cheeks and bridge of the nose. Further, due to the higher flexibility of the cloth and surgical mask material, they easily deform during exhalation, causing an increase in the size of the preexisting gaps, allowing more aerosols to escape.

[snip]

In order to further evaluate the effect of leakage through the gaps around the cheeks and the nose, a separate case with the KN95 mask was considered with 3 mm gaps created artificially, as described in Sec. II. The 3 mm gaps are representative of the typical gaps observed for the surgical and cloth masks and provide a “loose-fitting” KN95 case. Results for the KN95-gap case in Fig. 6 and Table III show a significant reduction in the filtration efficiency compared to the baseline KN95 mask, with [eta] decreasing from 46.3% to a paltry 3.4%.

[snip]

The instantaneous particle concentrations measured within the field of view in Fig. 7(a) show large temporal variations in local concentrations when masks are used, which consistently exceed those seen for the no-mask case....The implication for disease mitigation is a significant temporal variability in the exposure risk associated with masks in an unventilated indoor environment.

The results show that a standard surgical and three-ply cloth masks, which see current widespread use, filter at apparent efficiencies of only 12.4% and 9.8%, respectively. Apparent efficiencies of 46.3% and 60.2% are found for KN95 and R95 masks, respectively, which are still notably lower than the verified 95% rated ideal efficiencies. Furthermore, the efficiencies of a loose-fitting KN95 and a KN95 mask equipped with a one-way valve were evaluated, showing that a one-way valve reduces the mask’s apparent efficiency by more than half (down to 20.3%), while a loose-fitting KN95 provides a negligible apparent filtration efficiency (3.4%).
I do not fully understand their method for characterising filtration efficiency. They seemed to compare the particle concentration with a mask to that without a mask and normalised it to that without a mask. They found the concentration using a "simple" diffusion equation which was fitted to experimental data and whose terms they use for their filtration estimation.

They found that surgical masks/cloths under the lab conditions was ~10% and for a loose fitting N95 which they claim is comparable to typical gaps observed in surgical masks, this drops to, and I quote, a "paltry 3.4%". They describe this as a "negligible apparent filtration efficiency" in the conclusions. This does not take into consideration that a good number of people do not wear masks properly anyway.

The problems with the study is that breaths are not just confined to containing droplets of one micrometre but also have larger droplets, which carry a greater volume of the ejected spray, are more likely to be filtered by the mask, with the likelyhood increasing with size of the droplet.

But if you combine this study with issues such as the possibility of people not properly socially distancing whilst wearing masks or the environmental impact (which is admittedly a different issue), where do you draw the line between saying they should be worn and saying they should not?
 
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Wibble

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An LED will not be powerful enough to illuminate sufficiently well the small droplets. You need a laser for non-intrusive measurements or a counting device. Even so, that video shows coughing and sneezing and those people should be self-isolating anyway. Sure, the horizontal penetration distance of the ejected spray is altered, but you still may release droplets into the environment.

There is also another important point as well. A jet with larger momentum (as is the case with no mask), if directed to the floor, will carry all its droplets some distance towards the floor. A jet redirected vertically upwards which has lower momentum is more likely to have its droplets become entrained in the air, simply because the interaction time between the droplets and surrounding air flow (called eddies) is larger.

I have actually found a paper (July 2021) where some researchers have used PIV to quantify some of the droplet characteristics alongside olive droplets with were fixed at about one micrometer:
https://aip.scitation.org/doi/pdf/10.1063/5.0057100

Some important points (quote tags omitted):
As previously noted, a significant quantity of aerosol escapes at the bridge of the nose in Figs. 4(b) (Multimedia view) and 4(c) (Multimedia view), which highlights the importance of the fit of the mask to the face. Here, the fit of each mask is typical of appropriate usage, with the straps tightened (as outlined in Sec. II) and the built-in wire shaped to the bridge of nose. Nonetheless, aerosols escape at the perimeter of the mask due to inevitable imperfections in the mask fit, with the most significant quantity of particles escaping at the bridge of the nose. Other leakage sites include the interface of the mask edges with the cheeks and lower jaw [not captured in Figs. 4(b) (Multimedia view) and 4(c) (Multimedia view) due to laser sheet positioning]; however, these results and other supplementary measurements (not shown for brevity) confirm that leakage at the bridge of the nose far exceeds all other leakage points.

[snip]

The results in Fig. 4 illustrate that a notable amount of particles leak out at the perimeter of all masks, which is expected to result in notably lower effective filtration efficiency, compared to ideal filtration efficiency, when exhalation is considered.

[snip]

Noting the significance of both the ideal filtration characteristics (Sec. III A) and fit of a mask (Sec. III B), it is apparent that both effects must be taken into account in order to provide an accurate measure of the effectiveness of a mask in reducing the dispersion of an aerosol exhaled by an individual.

[snip]

The cloth and surgical masks perform relatively poorly with efficiencies of only 9.8% and 12.4%, respectively, due to both low material filtration efficiency and significantly higher amounts of leakages around the cheeks and bridge of the nose. Further, due to the higher flexibility of the cloth and surgical mask material, they easily deform during exhalation, causing an increase in the size of the preexisting gaps, allowing more aerosols to escape.

[snip]

In order to further evaluate the effect of leakage through the gaps around the cheeks and the nose, a separate case with the KN95 mask was considered with 3 mm gaps created artificially, as described in Sec. II. The 3 mm gaps are representative of the typical gaps observed for the surgical and cloth masks and provide a “loose-fitting” KN95 case. Results for the KN95-gap case in Fig. 6 and Table III show a significant reduction in the filtration efficiency compared to the baseline KN95 mask, with [eta] decreasing from 46.3% to a paltry 3.4%.

[snip]

The instantaneous particle concentrations measured within the field of view in Fig. 7(a) show large temporal variations in local concentrations when masks are used, which consistently exceed those seen for the no-mask case....The implication for disease mitigation is a significant temporal variability in the exposure risk associated with masks in an unventilated indoor environment.



I do not fully understand their method for characterising filtration efficiency. They seemed to compare the particle concentration with a mask to that without a mask and normalised it to that without a mask. They found the concentration using a "simple" diffusion equation which was fitted to experimental data and whose terms they use for their filtration estimation.

They found that surgical masks/cloths under the lab conditions was ~10% and for a loose fitting N95 which they claim is comparable to typical gaps observed in surgical masks, this drops to, and I quote, a "paltry 3.4%". They describe this as a "negligible apparent filtration efficiency" in the conclusions. This does not take into consideration that a good number of people do not wear masks properly anyway.

The problems with the study is that breaths are not just confined to containing droplets of one micrometre but also have larger droplets, which carry a greater volume of the ejected spray, are more likely to be filtered by the mask, with the likelyhood increasing with size of the droplet.

But if you combine this study with issues such as the possibility of people not properly socially distancing whilst wearing masks or the environmental impact (which is admittedly a different issue), where do you draw the line between saying they should be worn and saying they should not?
In a pandemic you make best guess rules based on the available data and err on the side of caution. Outside of a pandemic I don't think you can mandate them. But it would be nice of it became a habit when ill.
 

0le

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In a pandemic you make best guess rules based on the available data and err on the side of caution. Outside of a pandemic I don't think you can mandate them. But it would be nice of it became a habit when ill.
Yup, but you said the evidence was overwhelming, which it clearly is not.
 

Massive Spanner

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I haven't had a cold since early 2020. I'm assuming it's the same for a lot of people. What happens when we're all back in the office? Will we all get really bad colds or wha'? I assume my immune system won't be as effective as it was when I was getting two or three a year.
 

Wibble

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Yup, but you said the evidence was overwhelming, which it clearly is not.
It is overwhelming that that mask wearing helps. You can debate the degree due to which is does based on the imperfect data of course.
 

Stanley Road

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I haven't had a cold since early 2020. I'm assuming it's the same for a lot of people. What happens when we're all back in the office? Will we all get really bad colds or wha'? I assume my immune system won't be as effective as it was when I was getting two or three a year.
Same here, between Sept & Dec 2019 I had multiple head colds, flu symptoms. Nothing since. This will all change if we have to sit on packed transport and I expect loads of people will be in self isolation even at the hint of a sneeze
 

0le

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It is overwhelming that that mask wearing helps. You can debate the degree due to which is does based on the imperfect data of course.
So you would wear a mask, regardless if it made no statistically significant effect whatsoever?
 

golden_blunder

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I haven't had a cold since early 2020. I'm assuming it's the same for a lot of people. What happens when we're all back in the office? Will we all get really bad colds or wha'? I assume my immune system won't be as effective as it was when I was getting two or three a year.
The winter is going to be interesting, especially with public transport opening up to full capacity again
 

Massive Spanner

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The winter is going to be interesting, especially with public transport opening up to full capacity again
Yeah you'd imagine it's going to be a bastard of a flu season, and even in a normal winter flu season the HSE can't cope, so what happens when more people are in with the flu and Covid is still knocking about?

I'm dreading getting a packed train into work again.
 

Wibble

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So you would wear a mask, regardless if it made no statistically significant effect whatsoever?
If there was research that convinced me that it was meaningless I would stop. So far the evidence strongly suggests that it does help even if the exact benefit requires more data.

I might be a scientist at heart but in a pandemic you have to adopt the precautions principle as it is no longer purely an academic consideration.
 

jojojo

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Florida are currently demonstrating that just having vaccines available isn't enough - people have to actually take up the offer.


A reminder that the number to watch isn't how many are vaccinated, it's how many (particularly of the most vulnerable) aren't.
 

Dante

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I haven't had a cold since early 2020. I'm assuming it's the same for a lot of people. What happens when we're all back in the office? Will we all get really bad colds or wha'? I assume my immune system won't be as effective as it was when I was getting two or three a year.
I don't think it'll be any worse than usual.

There won't be two years' worth of colds and flus queuing up to get you, because there hasn't been two years' worth of widespread infecting and mutating to create new variants.

2022 should be more or less like 2019 in terms of seasonal bugs. Covid-19 has been like switching off the supermarket conveyor belt, rather than pushing back the items and waiting to release them in one go.