Genuine points of uncertainty

[Gfamily]

I do wonder how much of this is down to better, more frequent handwashing

It might be interesting to compare with rates of similar diseases here in NZ. Restrictions on movement and social gathering ended months ago, but the recommendation to wash and sanitise hands remains. Many shops and other venues still have hand sanitiser available at the entrance. So airborne transmission now is pretty much as it was before the pandemic, but hand hygiene is still better.

Are people still avoiding things like shaking hands when meeting friends?

[basementer]

What we are seeing is a massive reduction in other infectious diseases across the board. The records at work are showing about a 10th of the usual levels of things like norovirus, ILI, Strep A and Varicella. This isn't reduced willingness to see the Dr as we aren't seeing much from care homes, hospitals and other settings where they are fully aware of their legal duty to report these. Normally around now we'd see 40+ new norovirus outbreaks a day and often 60-70. We've not recorded 10 all week.

I do wonder how much of this is down to better, more frequent handwashing

It might be interesting to compare with rates of similar diseases here in NZ. Restrictions on movement and social gathering ended months ago, but the recommendation to wash and sanitise hands remains. Many shops and other venues still have hand sanitiser available at the entrance. So airborne transmission now is pretty much as it was before the pandemic, but hand hygiene is still better.

Are people still avoiding things like shaking hands when meeting friends?

Good point. No, IME hand shaking between friends is back to normal. I have a bit of hesitation about shaking hands when meeting someone for the first time though. I wait for their lead rather than offering my hand.

[lpm]

What the f.ck? What kind of f.cking idiots still keep f.cking shaking f.cking hands? It's unbelievably rude to offer your hand to shake. Kill this primitive and barbaric custom.

[OneOffDave]

It might be interesting to compare with rates of similar diseases here in NZ. Restrictions on movement and social gathering ended months ago, but the recommendation to wash and sanitise hands remains. Many shops and other venues still have hand sanitiser available at the entrance. So airborne transmission now is pretty much as it was before the pandemic, but hand hygiene is still better.

Cross country studies would be really interesting. The other study that might be interesting is to look at ILI/noro/gastro outbreaks in care homes over the previous few years and the case/death rates from COVID-19 and see if there's a correlation in high numbers in either measure

[Squeak]

Australian flu tracking still had very low rates of flu symptoms, though you can't compare with other years in January because they don't usually bother to run the survey through summer.

https://info.flutracking.net/reports-2/ ... a-reports/

[Woodchopper]

Back to aerosol transmission.

Interesting account of how assumptions about aerosol transmission were wrong, and based on an error.
https://www.wired.com/story/the-teeny-t ... ovid-kill/

[JQH]

Interesting read - and shows just how hard it is to shift established errors.

[shpalman]

Back to aerosol transmission.

Interesting account of how assumptions about aerosol transmission were wrong, and based on an error.
https://www.wired.com/story/the-teeny-t ... ovid-kill/

For example, the 5 µm cutoff between aerosols and droplets was in this:

I'm reading Modelling aerosol transport and virus exposure with numerical simulations in relation to SARS-CoV-2 transmission by inhalation indoors https://doi.org/10.1016/j.ssci.2020.104866

In a recent study (Leung et al., 2020) on the efficacy of facial mask in reducing the risk of coronavirus transmission via droplets and aerosols, the viral RNA was detected in 30% of the larger droplets (> 5 µm) while it was detected in 40% of the smaller aerosols (< 5 µm). It is also recently argued that the small aerosols (< 5 µm) exhaled in normal speech plausibly serve as an important and under-recognized transmission agent for SARS-CoV-2 (Asadi et al., 2020).

Pubs and restaurants need to stay closed. Talking while you have your mask off to eat or drink spreads the virus. No, you can't go to the pub or restaurant with people you live with anyway, you can perfectly well eat or drink together at home. Get a takeway, whatever. Paying pubs directly to stay closed would be cheaper in the long run than subsidizing people to go to them and then dealing with the resulting wave of infection. https://www.theguardian.com/business/20 ... e-in-covid

What I'm not sure about, is if there's any evidence that any of the measures we're taking to reduce contagion from aerosols or fomites are counterproductive. So if contagion is persisting it's because we're not doing them properly or not doing them enough.

[Herainestold]

It now seems most of the transmission is aerosol, which explains many of the super spreader events. Fomites, not so much.
It is unfortunate that the timing of this information is just as mask mandates are being rolled back in America, because masks are one of the few mitigations that work with aerosol transmission. It also points to the danger of outside spread when tiny aerosol particles can waft on the breezes for hundreds of metres.

[discovolante]

This may be entirely spurious as I'm not a behavioural scientist, but in regions where compliance with mask wearing is already low, would it not be potentially counterproductive to mandate outdoor mask wearing in case people decide 'f.ck that' and decide to meet indoors instead, which is known to be much more risky with or without masks? I'm not really sure if it would have anything more than a marginal effect though. Meeting outdoors seems to be about the least risky thing you can do however, and if people are going to be meeting anyway it seems like making outdoor meeting as easy and pleasant as possible might be the best approach at the moment.

[headshot]

It now seems most of the transmission is aerosol, which explains many of the super spreader events. Fomites, not so much.
It is unfortunate that the timing of this information is just as mask mandates are being rolled back in America, because masks are one of the few mitigations that work with aerosol transmission. It also points to the danger of outside spread when tiny aerosol particles can waft on the breezes for hundreds of metres.

Evidence or STFU.

[Sciolus]

Back to aerosol transmission.

Interesting account of how assumptions about aerosol transmission were wrong, and based on an error.
https://www.wired.com/story/the-teeny-t ... ovid-kill/

That seems very poor. The biophysics of respirable particles is pretty well understood, based on 70 years of study first in the nuclear world, then in the context of air pollution. Anyone in those fields will tell you that a 10 ug diameter particle is basically neutrally buoyant --- that's an order of magnitude more virus per particle than 5 ug. The behaviour of different size particles in the lungs likewise --- 10 ug is respirable but won't penetrate deep into the lungs, 2.5 ug will penetrate deeper, 0.1 ug will cross into the bloodstream, etc. (or something like that).

The real uncertainty, at least from what I can determine since you would expect it to vary between different pathogens, is around:
- How many viruses are ejected per cough, and what is the size distribution of particles;
- What is the lifetime of virus within an aerosolised particle;
- What viral load needs to be inhaled to what depth in the lungs to cause an infection.
If you know those, determining infection risk in various conditions is pretty* easy. I assume that was what was behind the 15 minute thing in early advice, but I may have been giving them too much credit.

[basementer]

Back to aerosol transmission.

Interesting account of how assumptions about aerosol transmission were wrong, and based on an error.
https://www.wired.com/story/the-teeny-t ... ovid-kill/

10 ug diameter

?

[shpalman]

Also it's not hard to write μ.

[sTeamTraen]

This may be entirely spurious as I'm not a behavioural scientist, but in regions where compliance with mask wearing is already low, would it not be potentially counterproductive to mandate outdoor mask wearing in case people decide 'f.ck that' and decide to meet indoors instead, which is known to be much more risky with or without masks?

People generally behave in a first-order way (and even then, it takes something pretty big to change that). Remember last March when some people were arguing that "lockdown fatigue" would set in? I'm not aware of it happening anywhere. Masks have been required on the street here since last June and (N=1 anecdotally) I would say compliance has actually gone up over time, as things like "getting used to it", "discovering it's not so bad", and "no longer forgetting the mask at home" seem to have greatly outweighed any "fatigue".

I think at some point in the past 10-15 years, moderately well-educated laypeople fell a bit too much for some of the cuter ideas of social psychology and other behavioural sciences, perhaps influenced by authors like Gladwell and the Freakonomics people. With some of the stuff that comes out of places like the Nudge Unit, it seems that there is a constant search for the counter-intuitive, because that would be a neater story.

The hard part is working out where people genuinely do behave in a "paradoxical" or otherwise unexpected way, but one of the reasons why psychology is hard is because those situations are quite rare.

[Millennie Al]

masks are one of the few mitigations that work with aerosol transmission.

That depends on what you mean by "masks". The right type of mask when properly worn can greatly reduce transmission, but merely making mask wearing mandatory is very much less effective. Meny people will wear a mask which has little effect - plain fabric which is not much more than decporative. Of those who wear a suitable mask, few wear it properly. Have a look at the people around you when you are next out. You'll see people with surgical style masks where the conformable nose part has not been adjusted, leaving a big gap. Similarly, you'll see many with obvious gaps at the side due to bad fit or bad adjustment. And, of course, you'll also see people using them covering only the mouth or as chin warmers not even covering the mouth.

The really effective way to prevet transmission is to keep people apart. And when people must be near one another, to provide sufficient ventilation, (which can be trivially done by meeting outdoors).

[Sciolus]

Back to aerosol transmission.

Interesting account of how assumptions about aerosol transmission were wrong, and based on an error.
https://www.wired.com/story/the-teeny-t ... ovid-kill/

10 ug diameter

?

Brain fart, I was talking about particle diameters so it should course been um (terribly sorry, μm or possibly µm depending which part of the Unicode Consortium you believe). But the amount of stuff inhaled will likely be measured in ug.

[sTeamTraen]

masks are one of the few mitigations that work with aerosol transmission.

That depends on what you mean by "masks". The right type of mask when properly worn can greatly reduce transmission, but merely making mask wearing mandatory is very much less effective. Meny people will wear a mask which has little effect - plain fabric which is not much more than decporative. Of those who wear a suitable mask, few wear it properly. Have a look at the people around you when you are next out. You'll see people with surgical style masks where the conformable nose part has not been adjusted, leaving a big gap. Similarly, you'll see many with obvious gaps at the side due to bad fit or bad adjustment. And, of course, you'll also see people using them covering only the mouth or as chin warmers not even covering the mouth.

But even a poorly-worn mask provides more protection than no mask. It's not a spacesuit that is either perfectly airtight or completely useless. As long as someone has a big ol' barrier in front of their mouth when they're taking to me from 2 metres away, that's already a big difference. The aerosols coming out of their nose start off heading for the ground (and nostrils are a lot narrower than a mouth).

Pretty much everything about public health is statistical. Every little helps, every big behaviour changer helps more, but getting to zero Covid isn't going to happen. At some point both the spread and lethality of Covid actually are going to be low enough to be comparable with an average flu season, and at that point we will have to accept that life does not have zero risk and move on a bit. (That said, I expect local Covid outbreaks to become a staple of news media for a couple of decades. It took about that amount of time for newspapers to stop reporting every single case of Legionnaires Disease on another continent.)

[jimbob]

masks are one of the few mitigations that work with aerosol transmission.

That depends on what you mean by "masks". The right type of mask when properly worn can greatly reduce transmission, but merely making mask wearing mandatory is very much less effective. Meny people will wear a mask which has little effect - plain fabric which is not much more than decporative. Of those who wear a suitable mask, few wear it properly. Have a look at the people around you when you are next out. You'll see people with surgical style masks where the conformable nose part has not been adjusted, leaving a big gap. Similarly, you'll see many with obvious gaps at the side due to bad fit or bad adjustment. And, of course, you'll also see people using them covering only the mouth or as chin warmers not even covering the mouth.

But even a poorly-worn mask provides more protection than no mask. It's not a spacesuit that is either perfectly airtight or completely useless. As long as someone has a big ol' barrier in front of their mouth when they're taking to me from 2 metres away, that's already a big difference. The aerosols coming out of their nose start off heading for the ground (and nostrils are a lot narrower than a mouth).

Pretty much everything about public health is statistical. Every little helps, every big behaviour changer helps more, but getting to zero Covid isn't going to happen. At some point both the spread and lethality of Covid actually are going to be low enough to be comparable with an average flu season, and at that point we will have to accept that life does not have zero risk and move on a bit. (That said, I expect local Covid outbreaks to become a staple of news media for a couple of decades. It took about that amount of time for newspapers to stop reporting every single case of Legionnaires Disease on another continent.)

Exactly. This has been pretty explicit in discussing vaccinations. That's why people talk about percent effectiveness.

The aim is to keep the virus declining. If R stays below 1 it will die out. Not being vaccinated to smallpox isn't a problem now.

Of course as well as that - it also protects the individual. Likewise with masks. Two NPIs that each independently reduce the risk by 50% are 75% effective when combined.

[Millennie Al]

But even a poorly-worn mask provides more protection than no mask. It's not a spacesuit that is either perfectly airtight or completely useless.

Yes, but how much more? If it's 50% effective, that's great, but what if it's 1% effective? Is it then still worth it?

As long as someone has a big ol' barrier in front of their mouth when they're taking to me from 2 metres away, that's already a big difference. The aerosols coming out of their nose start off heading for the ground (and nostrils are a lot narrower than a mouth).

Droplets are stopped by masks, but fall to the ground easily also. That's where the 2 metre rule comes from (and the 1 metre rule in other places - it's not very exact). But you can get the same effect by having the person not face directly at you. Aerosols hang in the air, so in an enclosed space they accumulate, so the time you are there matters. Even if a mask was 50% effective, that would simply mean that you could stay longer for the same risk.

Pretty much everything about public health is statistical. Every little helps, ...

If the effectiveness of masks is low enough then they end up being harmful. People will do things that they otherwise wouldn't on the grounds that they're safe because masks are being worn. This is harmless if the activity itself is harmless, but many such activities are not.

[Herainestold]

But even a poorly-worn mask provides more protection than no mask. It's not a spacesuit that is either perfectly airtight or completely useless.

Yes, but how much more? If it's 50% effective, that's great, but what if it's 1% effective? Is it then still worth it?

As long as someone has a big ol' barrier in front of their mouth when they're taking to me from 2 metres away, that's already a big difference. The aerosols coming out of their nose start off heading for the ground (and nostrils are a lot narrower than a mouth).

Droplets are stopped by masks, but fall to the ground easily also. That's where the 2 metre rule comes from (and the 1 metre rule in other places - it's not very exact). But you can get the same effect by having the person not face directly at you. Aerosols hang in the air, so in an enclosed space they accumulate, so the time you are there matters. Even if a mask was 50% effective, that would simply mean that you could stay longer for the same risk.

Pretty much everything about public health is statistical. Every little helps, ...

If the effectiveness of masks is low enough then they end up being harmful. People will do things that they otherwise wouldn't on the grounds that they're safe because masks are being worn. This is harmless if the activity itself is harmless, but many such activities are not.

Most transmission is aerosols. Masks work by containing the cloud of virions inside your mask instead of expelling it to the surroundings. Obviosly, fit and avoiding leakage is important. A medical procedure mask with a cloth mask over it is much better than either one worn singly.
Inside ventilation is key, avoid crowded poorly ventilated places.
Most transmission is ocurring when people are unmasked, eating, drinking, talking. So don't do it.

[Grumble]

Most transmission is ocurring when people are unmasked, eating, drinking, talking. So don't do it.

Pretty hard to eat or drink with a mask on.

[sTeamTraen]

If the effectiveness of masks is low enough then they end up being harmful. People will do things that they otherwise wouldn't on the grounds that they're safe because masks are being worn. This is harmless if the activity itself is harmless, but many such activities are not.

I don't think this is necessarily true. Your model basically proposes that people want to do X and will do it without further concern as soon as they consider that they have done enough to make themselves safe. That might be the case much of the time (we know that on average people drive cars at a roughly constant level of perceived risk), but in the case of Covid, at least, it seems to me that the people who are most assiduous about wearing masks are also being careful in other ways (because they don't think the mask is completely sufficient), whereas the ones who are sloppy with masks are also taking other risks.

Human behaviour is complicated, non-linear, situation-specific, and often not strictly rational. That's why psychologists are still in business.

[shpalman]

If the effectiveness of masks is low enough then they end up being harmful. People will do things that they otherwise wouldn't on the grounds that they're safe because masks are being worn. This is harmless if the activity itself is harmless, but many such activities are not.

I don't think this is necessarily true. Your model basically proposes that people want to do X and will do it without further concern as soon as they consider that they have done enough to make themselves safe. That might be the case much of the time (we know that on average people drive cars at a roughly constant level of perceived risk), but in the case of Covid, at least, it seems to me that the people who are most assiduous about wearing masks are also being careful in other ways (because they don't think the mask is completely sufficient), whereas the ones who are sloppy with masks are also taking other risks.

Human behaviour is complicated, non-linear, situation-specific, and often not strictly rational. That's why psychologists are still in business.

There was enough well akshully from "experts" about masks last year.

Except I was wrong because we didn't learn enough, either in Italy or the UK, to stop the second wave being similarly deadly to the first one. Well, morons gotta morr I suppose.

My worry is that by Italy switching to criteria based on hospital occupancy to judge whether the covids are serious enough to merit control or containment measures, we'll be throwing away a couple of weeks of advance warning in a similar way to how we basically carried on as normal during the obvious exponential growth in October.

[discovolante]

This may be entirely spurious as I'm not a behavioural scientist, but in regions where compliance with mask wearing is already low, would it not be potentially counterproductive to mandate outdoor mask wearing in case people decide 'f.ck that' and decide to meet indoors instead, which is known to be much more risky with or without masks?

People generally behave in a first-order way (and even then, it takes something pretty big to change that). Remember last March when some people were arguing that "lockdown fatigue" would set in? I'm not aware of it happening anywhere. Masks have been required on the street here since last June and (N=1 anecdotally) I would say compliance has actually gone up over time, as things like "getting used to it", "discovering it's not so bad", and "no longer forgetting the mask at home" seem to have greatly outweighed any "fatigue".

I think at some point in the past 10-15 years, moderately well-educated laypeople fell a bit too much for some of the cuter ideas of social psychology and other behavioural sciences, perhaps influenced by authors like Gladwell and the Freakonomics people. With some of the stuff that comes out of places like the Nudge Unit, it seems that there is a constant search for the counter-intuitive, because that would be a neater story.

The hard part is working out where people genuinely do behave in a "paradoxical" or otherwise unexpected way, but one of the reasons why psychology is hard is because those situations are quite rare.

Hm, I'm not really sure I'm looking for a counter-intuitive prediction, just a fairy standard 'if you stop people doing stuff they want to do, people (but not everyone) will often keep doing it, but where you can't see them'. But I think it's fair to say that people get used to masks etc and probably one of the biggest reasons why what I suggested might happen probably wouldn't happen is because enforcement of non-mask wearing seems to be fairly weakly enforced, as far as I can gather - I might be wrong - but it would be even more difficult to enforce outside, again as I say in places where compliance isn't more or less universal. And I'm also not sure what proportion of the public would prefer to risk meeting indoors than be forced to wear a mask outside, it might be pretty low.