How could wearing a mask help build immunity to COVID-19? It’s all about the viral dose


Larisa Labzin, The University of Queensland

People infected with SARS-CoV-2, the virus that causes COVID-19, can spread the virus when they speak, sing, cough, sneeze or even just breathe. Scientists think face masks help limit virus spread by protecting everyone else from the infected wearer. As a result, face maks are now mandatory in many cities, states and countries to limit the spread of COVID-19.

People typically wear surgical, cloth or other face coverings that don’t completely prevent the virus from infecting the wearer, though medical grade surgical masks do appear to offer more protection. Nonetheless, these don’t have the same level of protection as N95 or P2 “respirator” masks worn by many health-care workers. Additionally, how we wear the mask matters, as touching it often and not completely covering the nose and mouth renders it ineffective.

While these face coverings may not completely prevent us from getting infected with COVID-19, they probably reduce the number of virus particles we inhale — the “viral dose”. Scientists think a lower viral dose can reduce the severity of the disease we get. Indeed, where universal face masking is implemented, a much higher proportion of new infections with COVID-19 are asymptomatic.

Could this lower viral dose help us build some immunity to the disease? Two researchers from the University of California have raised this possibility, writing in the prestigious New England Journal of Medicine. Although the theory hasn’t been proven yet.

The dose makes the poison

How much virus we are initially infected with is a key determinant of how sick we get, according to evidence from other viruses and animal studies. We also know this is true in hamsters that have been experimentally infected with SARS-CoV-2.

Imagine if you touch a door handle that happens to have one virus particle on it, and then touch your nose and breathe that particle in. You will be infected with that one virus particle. One estimate, published in the Lancet, suggested one SARS-CoV-2 virus particle will have replicated to make nearly 30 new virus particles in 24 hours. Those 30 new particles can then go on to infect 30 more cells, giving rise to 900 new particles in the next 24 hours or so.

Now imagine someone sneezes right in your face and you inhale 1,000 virus particles. After one round of replication you could have 30,000 particles, and then 900,000 in the round after. In the same period of time your body could be dealing with 1,000 times more virus, compared to the first scenario.

How different types of masks work to block droplets from talking, coughing and sneezing (Thorax).

Once the immune system detects the virus, it has to race to get it under control and stop it replicating. It does this in three main ways:

  • telling our cells how to disrupt viral replication

  • making antibodies that recognise and neutralise the virus to stop it infecting more cells

  • making T cells that specifically kill virus-infected cells.

While the first step is relatively quick, creating specific antibodies and T cells takes days or even weeks. Meanwhile, the virus is replicating over and over again. So the initial dose of virus really determines how much of the body the virus has infected before the immune system kicks fully into gear.

What about for long-term immunity?

The more virus there is, the bigger the immune response has to be to control it. And it’s the immune response that actually causes the symptoms, like fever. In an asymptomatic infection, we think the immune system has probably managed to get the virus under control early on, so the immune response itself is possibly smaller, and so we won’t see any symptoms.

We also think many cases of very severe COVID-19 might really be a result of the immune system overreacting. This is why the steroid treatment dexamethasone, which suppresses the immune response, shows promise in treating severe cases (but not mild ones).




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After we clear an infection, we keep some immune cells around in case we get infected again. These are B cells, which produce antibodies specific to SARS-CoV-2, and T cells, which kill virus-infected cells. This is also the premise behind vaccination: we can trick the immune system into making those SARS-CoV-2 specific cells without having been infected.

Because face masks might allow a small number of virus particles through, wearers might be more likely to get asymptomatic infections. This might be enough to protect them from future infection with SARS-CoV-2. So if we are in a situation where there is high community transmission, and we can’t always maintain physical distance, wearing a face mask might be a factor that helps us in the long run.

It’s another argument in favour of masks

While this sounds promising, there’s still a lot we don’t understand. We don’t know yet whether an asymptomatic infection would generate enough immunity to guard against future infection — or if this is even measurable.

Viral dose is likely to be just one factor among many that determines how sick someone gets with COVID-19. Other factors include age, sex, and other underlying conditions. Finally, even with asymptomatic infections, we don’t know yet what the long term effects of COVID-19 are. It’s best to avoid getting COVID-19 altogether if possible.

Nevertheless, this is yet another reason to keep wearing face masks. As many cases of COVID-19 are asymptomatic, we could still be transmitting the virus even without symptoms. That’s why wearing a mask is a responsible thing to do, even if we feel fine.




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The Conversation


Larisa Labzin, Research Fellow, Institute for Molecular Bioscience, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Does your homemade mask work?



Ti Vla/Shutterstock

Simon Kolstoe, University of Portsmouth

If a surgeon arrived at the operating theatre wearing a mask they had made that morning from a tea towel, they would probably be sacked. This is because the equipment used for important tasks, such as surgery, must be tested and certified to ensure compliance with specific standards.

But anyone can design and make a face covering to meet new public health requirements for using public transport or going to the shops.

Indeed, arguments about the quality and standard of face coverings underlie recent controversies and explain why many people think they are not effective for protecting against COVID-19. Even the language distinguishes between face masks (which are normally considered as being built to a certain standard) and face coverings that can be almost anything else.

Perhaps the main problem is that, while we know that well-designed face masks have been used effectively for many years as personal protective equipment (PPE), during the COVID-19 outbreak shortages of PPE have made it impractical for the entire population to wear regulated masks and be trained to use them effectively.

As a result, the argument has moved away from wearing face masks for personal protection and towards wearing “face coverings” for public protection. The idea is that despite unregulated face coverings being highly variable, they do, on average, reduce the spread of virus perhaps in a similar way as covering your mouth when you cough.

But given the wide variety of unregulated face coverings that people are now wearing, how do we know which is most effective?

The first thing is to understand what we mean by effective. Given that coronavirus particles are about 0.08 micrometres and the weaves within a typical cloth face covering have gaps about 1,000 times bigger (between 1 and 0.1 millimetres), “effectiveness” does not mean reliably trapping the virus. Instead, much like covering our mouths when we cough, the aim of wearing cloth coverings is to reduce the distance that your breath spreads away from your body.

The idea is that if you do have COVID-19, depositing any virus you may breathe out on either yourself or nearby (within one metre) is much better than blowing it all over other people or surfaces.

So an effective face covering is not meant to stop the wearer from catching the virus. Although from a personal perspective we might want to protect ourselves, to do so we should be wearing specially designed PPE such as FFP2 (also known as N95) masks. But, as mentioned, by doing so we risk creating mask shortages and potentially putting healthcare workers at risk.

Instead, if you want to avoid catching the virus yourself, the most effective things to do are avoid crowded places by ideally staying at home, don’t touch your face, and wash your hands often.

Two simple tests

If effectiveness for face coverings means preventing our breath travelling too far away from our bodies, how would we go about comparing different designs or materials?

Perhaps the easiest way, as demonstrated by several increasingly shared pictures or videos on social media, is to find someone who “vapes” and film them breathing out the vapour while wearing a face covering. One glance at such a picture dispels any suggestion that these face coverings stop your breath escaping.

Instead, these pictures show that your breath is directed over the top of your head, down onto your chest, and behind you. The breath is also turbulent, meaning that although it does spread out, it doesn’t go far.

In comparison, if you look at a picture of someone not wearing a face covering, you will see that the exhalation goes mostly forward and down, but a significantly further distance than with the face covering.

Such a test is probably ideal for examining different designs and fits. Do coverings that loop around the ears work better than scarves? How far under your chin does a covering need to go? What is the best nose fitting? How do face shields compare to face masks? These are all questions that could be answered using this method.

But, in conducting this experiment, we should appreciate that “vaping” particles are about 0.1 to 3 micrometres – significantly bigger than the virus. While it is probably fair to assume that the smaller virus particles will travel in roughly the same directions as the vaping particles, there is also the chance that they may still go straight forward through the face covering.

To get an idea of how much this might happen, a simple test involving trying to blow out a candle directly in front of the wearer could be tried. Initially, the distance coupled with the strength of exhalation could be investigated, but then face coverings made from different materials and critically with different numbers of layers could be tried. The design of face covering that made it hardest to divert the candle flame will probably provide the best barrier for projecting the virus forward and through the face covering.

Trying to blow out a candle using different masks.

Without any more sophisticated equipment, it would be difficult to conduct any further simple experiments at home. However, combining the above two tests would provide wearers with a good idea about which of their face coverings would work the best if the aim was to avoid breathing potential infection over other people.The Conversation

Simon Kolstoe, Senior Lecturer in Evidence Based Healthcare and University Ethics Advisor, University of Portsmouth

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Are you wearing gloves or a mask to the shops? You might be doing it wrong



Shutterstock

Maximilian de Courten, Victoria University; Barbora de Courten, Monash University, and Vasso Apostolopoulos, Victoria University

Many people in the community are wearing face masks and gloves in an attempt to protect themselves against the coronavirus.

They might put on these items to go to the shops, or perhaps when taking a walk through the neighbourhood.

The evidence on whether these measures will actually protect against coronavirus is mixed and largely inconclusive.

But you’re even less likely to get protection if you don’t take care when putting on these items, while you’re wearing them, and when you take them off.




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Are masks recommended?

In Australia, the Department of Health states you don’t need to wear a mask if you’re well.

People self-isolating with symptoms suspected to be COVID-19 are advised to wear a surgical face mask when other members of their household are in the same room.

This is in line with recommendations from other countries and the World Health Organisation.

Some countries, particularly those with higher rates of COVID-19 than Australia, provide different advice. The Centers for Disease Control (CDC) in the United States recommend the use of masks, or cloth face coverings, more widely.

In Hong Kong, face masks are obligatory for everyone taking public transport.




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So do masks protect against COVID-19?

We should first separate the two distinct functions of a face mask: protecting others from being infected by a wearer, and protecting the wearer from infection.

SARS-CoV-2, the coronavirus that causes COVID-19, is transmitted via droplets that fly out of our mouths or nose: most commonly when when we cough or sneeze, but also when we speak.

Most of these particles range in size between 0.3-10 micrometers. They can be directly inhaled or land on a surface where we pick them up on our hands before touching our face.

The current thinking is face masks worn by an infected person can protect the people around them by filtering at least some of these particles, particularly larger ones. This constitutes the former of the two functions, and is known as “source control”.




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Coronavirus: how worried should I be about the shortage of face masks? Or can I just use a scarf?


Regarding the latter – protecting the wearer from infection – there’s some research on this, but not for COVID-19 specifically.

Evidence has shown the use of masks among health-care workers can reduce their infection with various other coronaviruses – so masks are an important element of PPE.

But for people in the community who appear to be healthy, we need more research before we can draw firm conclusions on the benefits of masks.

Are you doing it wrong?

Whatever the state of the science, some people appear to be doing things that could defeat the purpose of wearing a mask. Examples include pulling the mask under their chin for a “breather” or to make a phone call; or touching the mask while wearing it.

Through these actions, you can transfer the virus directly from your hands or your mobile phone to your face, increasing your risk of being infected.

The WHO has published some dos and don’ts for wearing face masks, summarised here:



What about gloves?

Gloves prevent the transmission of germs if used properly, and are an integral part of PPE for health-care workers.

If you’re suspected or confirmed to have COVID-19 and you’re isolating at home, Australian guidelines recommend anyone wanting to clean your room should put on a mask and gloves before entering.

However, gloves have not been recommended as a precautionary measure against COVID-19 for the average citizen. That’s largely because of the evidence we have about how the disease is, and isn’t, transmitted.

The virus is not absorbed through skin, so you can’t contract COVID-19 through touch alone. To acquire coronavirus through touch, you would have to touch a contaminated surface and then touch your face.

Although it is possible, scientists believe a much smaller proportion of infections happen this way, as compared to when an uninfected person inhales virus-carrying droplets emitted directly from an infected person.




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In the US where there are much higher rates of COVID-19 than in Australia, the CDC also suggests the use of gloves only in two coronavirus-related scenarios:

Wear them right

While there’s no evidence to suggest wearing gloves in the community will protect you, if you do choose to wear them, there are some things you should consider.

Importantly, if you still touch your face with your gloved hands – or even touch your mobile phone – this renders the gloves useless.

And if you’re not careful, you can also contaminate your hands when you put on or take off gloves.

So follow these steps when removing gloves to reduce the risk of contaminating your hands in the process.


The Conversation


Maximilian de Courten, Professor in Global Public Health, Victoria University; Barbora de Courten, Professor and Specialist Physcian, Monash University, and Vasso Apostolopoulos, Pro Vice-Chancellor, Research Partnerships, Victoria University

This article is republished from The Conversation under a Creative Commons license. Read the original article.