How often does a face mask stop a virus?

[Goonshow]

I'm curious about this. It now appears to be widely accepted that a face mask helps stop a virus spreading. But how often does a single mask do the job and save a single infection?

I think it happens rarely. I don't think masks stop the virus much, if at all, and I find the blind acceptance that they do puzzling.

My initial guess is that a mask worn by someone each day will stop transmission of the virus less than once a year.

Anyone else care to give their thoughts?

Yes, I saw he had Covid. That's why I don't want to sit next to him in the first place. If I have to though, I'm less than convinced a poorly written piece of paper or fabric will do anything to stop me getting it, so no, I don't care about it.

*store!!

*poorly worn

To everybody who has replied to this thread - I do not appear to have explained myself sufficiently. I'll have one last try.

I'm not querying the effectiveness of a mask. I'm simply asking the question: how many infections are masks stopping?

The whole rationale for wearing masks is to stop the virus passing from one person to another. I know that this is about attempting to reduce the overall risk, but when it boils down to it, the point of wearing a mask is that, now and then, it will be a barrier to a virus, and stop it transferring from one person to another. But how often does that happen on an individual level?

We appear to have adopted wearing masks on the premise that they can't do any harm and might do some good. I have never seen any estimates of how many infections they might stop.

Now, to my crude estimates. Of course they are estimates. We cannot know how many times a mask stops a virus. However, I still maintain that my simple formula is one that must be true.

If a number of people wear a mask for a number of days, then how often (on average) a single mask prevents a transmission will determine the number of infections that have been prevented.

That statement must be true. If you want to maintain that it is not true, please explain why.

There are 3 variables to this equation. The number of people wearing a mask each day, the number of infections prevented, and the frequency an infection is prevented.

We do not have exact figures for any of these. The only one that we can estimate with any kind of confidence is the number of people wearing a face covering daily.

In my examples I have given this a value of 25 million. You can use a higher or lower figure. I think that's a reasonable one. Use your own estimate if you wish.

If you then work on 25 million people a day, you can demonstrate how often a mask needs to repel a virus to achieve a particular number of infections that have been prevented.

The higher the number of prevented infections is achieved, the higher the frequency will be of an average face covering successfully preventing virus transmission.

You can produce a table showing how often this happens depending on total infections prevented.

So, if 25 million people wearing masks every day saves a million cases a day, each mask on average is stopping an individual infection once every 25 days.

To stop 100,000 infections a day, each of the 25 million masks is stopping the virus on average once every 250 days.

If infections are reduced by 10,000 a day, an individual mask is stopping a virus transmission once every 2500 days.

We can look at these scenarios and judge how likely each of them might be. My own view is that, currently, the maximum number of infections that face coverings can be preventing daily will not be higher than 10,000, and is probably closer to 1,000 a day. You may have a different view. It doesn't seem likely to me that 1 million transmissions are being saved every day. Does that seem likely to you?

Of course, many factors will impact on each face covering's individual chances of successfully achieving a single repulsion of the virus to prevent an infection. The type of mask worn, the way it is worn, for how long each day that mask is worn, where it is worn and by whom, will all have a huge impact. Most importantly, the prevalence of the virus will have a huge say in whether or not the face covering even comes anywhere near the virus.

None of that changes the basic rule. If you have the number of people wearing a mask and your target of saved transmissions that you wish to achieve, you can determine how often a single mask must stop the virus to achieve that number.

I raised this question because it has become an assumption that face coverings can do no harm and help stop transmission. I have seen nothing to indicate the numbers of prevented transmissions that might be achieved.

The numbers of saved infections might be so small that widespread mask wearing is no longer considered worthwhile. Another important point to consider is, when do we reach that point where face coverings are no longer worthwhile?

If they serve no purpose, why the hell are we being told to wear them? Why do medical professionals wear them? Why do surgeons wear them? Please somebody explain the reason behind them being mandatory if they're useless?

OP I think the reason no one wants to do your sums is that they are completely random and guesswork.

If I asked you to tell me how many drops of water fell on my roses, based on my guess that I get 30000 drops of water in my garden a year and my subsequent guess that my garden is 10 m by 10 m, give or take a bit... you could scribble numbers on the back of an envelope for hours but to what purpose??

Why are you engaging in this guesswork? And challenging others to do the same?

OP, you're clearly not scientifically minded, so stop trying to prove something that you have no clue about.
Start the trillionth antimask thread by all means, but don't dress it up as science.

@Goonshow,

You are still looking at this in a weird way! It only makes sense looking at a population (or at least sub population) level.

The goal is to reduce the r number below one. This will cause COVID cases to reduce and, eventually, be eliminated (apart from the odd local flare up), as they have done in China, Australia and New Zealand.

Mask wearing is one of many measures which reduce the r number (as shown by the studies I referenced above). There are many other measures including, crucially vaccination, but also social distancing, closure of schools, restaurants etc.

As the r number and cases come down, it is a question of priority which measures are eased first. Most would rather have schools and restaurants open and masks, as opposed to no masks but keeping restaurants closed.

If, when everything else has eased, the r number is still above 1, we need to keep mask wearing. If, however, it has sunk below 1, we can ditch masks.

Does that answer your question?

Are you asking for an actual number? "My mask stopped 14 covids" sort of thing?

How are people supposed to give you a meaningful figure? And if you feel like you know how to calculate one, then why don't you just be the one to supply the information instead of asking others to come up with graphs and calculations for you?

Dr Hilary was asked about the low flu rates this year and he said some years there are low rates and some there’s high rates and also we’re not mixing nearly as much either. Also more hand washing and tissue using. Wasn’t really anything to do with masks.

Well OP, when the new lockdown was announced on 30th December, I quickly nipped down to the car dealer to buy mats for my new car. They were intended to be my birthday present.

Despite me having phoned ahead, I had to hang around for about 10 minutes while they were fetched, there were two members of staff also hanging around, although more than 2m away and in a big airy space.

The next morning I developed a cough, so got a test - positive.

Did my mask prevent those 2 staff members getting Covid? I have no idea. But it presumably reduced the risk. Which is all that anyone has ever said they do.

So even if it takes 10,000 hours of mask wearing to prevent one transmission, it still helps reduce the R number. And in a pandemic, that is helpful. If the virus was rare, it wouldn’t be worth doing as a general measure, but would still be helpful in areas with higher infection rates.

Once the vaccine is fully rolled out it may be that we no longer need that reduction in R number, so can abandon masks.

I can only give my own experience of not catching it, despite approximately 12 lengthy visits to the hospital during the height of the pandemic, travelling on trains to get there, all whilst wearing FFP3 masks. I’ll clearly never know if I was just lucky and wouldn’t have caught it without the masks but I feel that they likely played a part in keeping me safe.

According to the latest SAGE review of studies on masks, they reduce transmission by 6 to 15% (15% would be similar to hand washing which sounds intuitively plausible). The impact can be higher (up to 45%) in specific circumstances:

assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/957010/s1029-emg-face-coverings-distancing.pdf

Face coverings worn in public, community and workplace settings are predominantly a source control, designed to reduce the emission of virus carrying particles from the mouth and nose of an infected person. This may have measurable benefits in reducing population level transmission when worn widely, through reducing the potential for asymptomatic or pre-symptomatic people spreading the virus without their knowledge. Analysis of regional level data in several countries suggest this impact is typically around 6-15% (Cowling and Leung, 2020, Public Health England 2021) but could be as high as 45% (Mitze et al., 2020). These figures should be treated with caution as it is not possible to establish the specific role of face coverings compared to other interventions in place at the same time or how transferable cases from other countries are transferable to the UK. Several modelling studies are reported within a recent systematic review (Howard et al., 2020) that also suggest substantial impacts on the value of R in a population, but are based on idealised assumptions around the efficacy and adherence to wearing face coverings.

In other words, masks are useful (especially in certain situations, e.g. at hairdressers) but they are very far from being the ultimate panacea to halt the spread of the pandemic.

aip.scitation.org/doi/10.1063/5.0016018

If you don't want to look up this or the thousands of other studies actually studying the extent to which different types of mask impede the travel of respiratory droplets in a lab, just watch the difference in cold weather between the amount of 'smoke' (as my 4 year old calls it) coming out of people's mouths with or without a mask.

Also, countries that adopted mask wearing early on have up to 100x fewer deaths than those that didn't. It's quite a strong correlation (you'll never be able to prove definitively that this was the main factor but it's very suggestive) globalnews.ca/news/7075024/mask-wearing-fewer-coronavirus-deaths/

I suspect that those countries that wore masks early also were those that took coronovirus seriously, unlike the UK so it's almost certainly not just the masks.

It doesn't really matter how much any individual mask stops transmission, it's a population risk mitigation. As PP have said, there is increasingly good evidence that ffp2/3 are much better at protecting the wearer, which is why it's an absolute scandal that not all health care workers have them.

OP you are not coming across as having a proper grasp of what you are talking about, so I have to assume you're just an anti-lockdown, anti-mask type trying (and failing) to prove some kind of a point. Which is pretty tiresome really.

The problem with modelling studies is that they indeed idealise assumptions around the efficacy and adherence to wearing face coverings. Unfortunately, some health agencies (and especially the US CDC) overemphasise the potential impact of masks turning the public health question into a major political and divisive issue.

I find the SAGE/PHE reports pretty balanced and objective. Masks help. 6 to 15% efficacy (going up to 45% in certain circumstances) is not negligible. It can be a swing factor between keeping R under 1 and letting the pandemic spiral out of control. However, masks are not "our ticket to freedom" and we should be aware that a small percentage of people who cannot wear masks are not going to kill thousands of grannies.

I think you might be a bit stupid

By the way, some of the "peer reviewed" papers "published in reputable medical journals" from last summer claiming that masks reduce spread by 60%+ had to be rescinded. States like Kansas and New Mexico that were highly praised for their "early mask mandates" and "prompt anti-COVID measures" ended up with higher death toll during the second wave than some (but not all) of their more "relaxed" neighbours.

Again, masks help. No, they are not going to make a 60%+ difference. We need to be realistic in our expectations.

I understand what you're saying OP, but I don't think many people on the thread do - they're just not understanding what you're getting at. Your reasoning might seem clear to you but it's not a type of thinking a lot of people are capable of, so it's going over people's heads.

I agree entirely with what you're saying.

40% of infections are occurring in hospitals, locations with strict infection protocols in place and proper PPE (though admittedly there have been failings and gaps on that side of things), so that's an interesting scenario to run your numbers on.

They is like swiss cheese innit. Wear loads mate. Blocks all your ‘oles up.

I see what you have tried to model, but there are many more variables that give viruses an advantage, or control. This study will give some ideas and it almost certainly won't be the first time you have seen it. The bus and the restaurant are pretty interesting to me:

english.elpais.com/spanish_news/2020-06-17/an-analysis-of-three-covid-19-outbreaks-how-they-happened-and-how-they-can-be-avoided.html
Admittedly you could say that masks aren't considered here, and that this is from the pre-Kent and SA period.

This seems to show that suitability or luck within the specific environment, plus masks and considering time spent (because it would seem that complete social distancing could not be part of this equation - perhaps between customers but not between healthy person and sick person), did work:

www.abc.net.au/news/2020-07-17/cdc-report-masks-may-limit-coronavirus-spread-hairdresser-us/12465958

OK, just noticed there is an inverted pyramid graphic in the el Pais article, at the end - masks are a small part of it but do make it onto one of the scale of the interventions to help control transmission (specifically mentioned in the bus analysis).

The whole rationale for wearing masks is to stop the virus passing from one person to another. I know that this is about attempting to reduce the overall risk, but when it boils down to it, the point of wearing a mask is that, now and then, it will be a barrier to a virus, and stop it transferring from one person to another. But how often does that happen on an individual level?

It doesn't matter the number of times it happens on an individual level, it matters what percentage of infections it prevents. It's all very well saying you estimate it only stops an infection once every 250 days (based on no evidence) but if individuals were only in a situation once in that 250 days where they are at risk of being infected, the mask would have been 100% effective. It's meaningless to say masks only stop X number of infections without the context of how many infections there would have been without masks ie expressing it as a percentage.

It would be true to say that the polio vaccine prevented no cases of polio in the UK last year because no one was exposed to the virus. Does that mean it is not effective?

A study in Beijing13, which examined the transmission of COVID-19 within families and close contacts of 335 people in 124 families from 28 February to 27 March 2020. They found that face mask use before the family member developed symptoms was 79% effective but that wearing a mask after the onset of illness was not significantly protective.

That is pretty good evidence that masks can be very effective in preventing transmission.

The concern that Sweden had about masks was that they give a false sense of security, encouraging people to get closer to each other than they otherwise would and thus creating more of a hazard rather than less.

One thing that I find nuts is the idea that teenagers can use masks effectively to prevent infection. One MN poster said her son had had four masks stolen, which about sums up the idiocy of believing that teens have any hope of coming anywhere near the required level of care to make masks even a tiny bit effective. In fact it seems bonkers to encourage teens to soak pieces of cloth in their (potentially infected) spit and snot then leave them around the place. Anyone who argues that teens definitely carefully put away their masks and never just drop them on their desk/throw them at another person/share them with friends has never met a teenager IMO.