We hear a lot about masks, even too much, and very little about the risk exposure based on the viral load. First of all, know that I am not for the use of the mask nor against the use of the mask. I consider that yes, it can be very useful, and that yes, there are measures currently that I find disproportionate to the risks. However, first and foremost, we should talk about the exposure to risks so that we can fully understand the package of measures within our reach and not just the idea of the mask.
A non-profit organization for the elderly asked us to discuss this topic. So, I repeat, it is not a question of being for or against, the important thing is to find out when it is really useful.
As you all know, the mask is now mandatory in Quebec in public transport and enclosed public areas since July 18: shops, offices, shopping centers, restaurants, etc. But why specifically enclosed public areas? Which activities are most at risk? We’re going to put numbers to all of this to help us breathe more freely.
Let’s talk about the mask, the risk exposure factors and the viral load from three angles:
- The use of the mask to limit the spread.
- Using a mask to reduce the chance of catching it.
- Risk exposure factors.
The use of the mask to limit the spread
Why wear a mask? Here is a statement from Quebec public health officials:
- Not all infected people have symptoms. “Some people can be infected without knowing it. Wearing a mask or face covering, also called a homemade mask, may help reduce the risk of an infected person spreading the virus to others.”
We don’t just put on the mask for ourselves, to keep us from catching it, but even more, for others, because a lot of people are asymptomatic. A recent study has shown that the amount of the SARS-CoV-2 coronavirus, known as the viral load, is higher in patients with milder symptoms who do not require hospitalization.
Here, I will go on a small tangent to talk about the information circulating on social networks. Firstly, the mask does not make you sick. If the mask made you sick, all of our surgeons and a lot of nurses would be sick. It can of course cause irritation or itching for those with sensitive skin and cause discomfort for some people with respiratory problems. This is of course unfortunate. When it comes to its effectiveness vs. virus size, keep in mind that it is not just a filter, but a partial barrier to deflect and reduce air movement. It is just like remembering to put your hand in front of your mouth to prevent a friend from being scared from your garlic breath. A mask would also reduce the spread of odor, reducing the flow of direct air to your friend. It’s the same with the virus: you need to reduce the flow of direct air to reduce the viral load in the air in which people around you breathe. I will come back to the effectiveness of masks with encrypted data later in this article.
Let’s define what the viral load is and why it is important. Viral load is a quantity of virus. For the infected person, this is the amount of virus that the person is carrying, but for the risk of infection, it is the amount of virus needed to infect another person. The lower the viral load needed to infect a person, the more contagious the virus is. It is also possible, according to a recent study by the Swiss Army, that a low viral load is linked to a lower risk of having symptoms of Covid-19 or the possibility of being asymptomatic. Thus, the mask could reduce the risk of developing Covid-19, even if you are infected, by reducing the viral load.
Coming back to asymptomatic people with a high viral load, you will understand that they have a greater ability to spread the virus for three reasons:
- They release more of the virus every time they breathe (not necessarily having to cough, but coughing does release more, of course.)
- They do not mistrust themselves since they do not feel sick.
- No one will deem them as suspicious because they don’t look sick.
It is therefore easy to understand that there may be asymptomatic people who spread the virus a lot and this is bound to be one of the most important problems of the current pandemic. This is why the use of the mask may be relevant to limit the spread.
Using a mask to reduce the risk of catching it
Interestingly, a Canadian study concludes that wearing a mask reduces the likelihood of being infected with the coronavirus by 85% when meeting an infected person. As previously mentioned, we unfortunately cannot know who is infected given the high rate of asymptomatic people.
A meta-analysis (the analysis of a large number of studies already published) considering 172 observational studies carried out in 16 countries and on six continents assessed that the rate of contamination of healthy people in contact with an individual affected by a transmissible virus in the air goes from 17.4% to 3.1% if they have facial protection. This equates to an 82% reduction, which is similar to the Canadian study. So, the mask also protects against the risk of catching it.
This protection of about 85% is in addition to that granted through distancing. Social distancing reduces the risk of infection from 12.8% to 2.6% (80% reduction) depending on whether you are within one meter or less of a person with COVID-19, and the efficiency increases beyond two meters of distance. This 80% and more reduction provided by social distancing is in addition to that of the mask when the mask is worn. We could therefore consider that the 80% applied to the residual 3.1% for people with a mask to give 0.62% (less than 1%). Hypothetically, based on the data presented (references at the end), the mask combined with the distancing would reduce the risks to less than 1%.
So, the mask is one of the tools, which must be used in consideration with social distancing and always, along with hand washing.
Here are the recommendations on how to put on and take off the mask by Dr Alain Vadeboncoeur: How to put on a mask or a face cover? (French Only)
As for the types of masks, WHO mentions that N95s are no more effective than conventional medical masks in dealing with COVID-19. Randomized controlled trials show “no difference” between these two face protectors in reducing the transmission of airborne infections.
It is of course true that cloth masks are not as effective as medical masks in general. To optimize fabric masks, they should have 3 layers and respect:
- an inner layer of absorbent material, such as cotton,
- an intermediate layer of non-woven material, such as polypropylene, and
- an outer layer of non-absorbent material, such as polyester or a polyester blend.
The mask should also allow breathing while speaking and walking quickly. It is certainly better to have one imperfect than not to have any at all. Also remember that just because you have a mask doesn’t mean you are completely protected. This is what brings me to discussing risk exposure factors.
Risk exposure factors
This is a very important topic for which I believe very little explanation has been given by public health officials. Most people know that the risk is higher in an enclosed area with poor ventilation than outside in the fresh air, because the risk of breathing air containing the virus is higher. What are the exposure factors other than a closed room?
Scientists have produced a COVID-19 risk index that I saw posted on social media, from a doctor friend in Belgium.
The index considers that the levels of exposure risks vary according to 4 main factors:
- closed spaces,
- the duration of the interaction,
- the crowd and
- forced exhalation.
Thus, activities are classified according to 5 levels of risk, from low to high:
- (Low) Stay home, take a walk outside, have a picnic, or go pick up an order by car.
- (Low/Medium) Remote sports activities outdoors, run errands, shopping.
- (Medium) Going to the emergency room, the dentist, taking a taxi, dining outside at a restaurant, visiting a museum.
- (Medium/High) Gyms, hairdresser/aesthetics, work in an office (with other people), restaurants and coffee shops located inside.
- (High) Indoor party, bar and nightclub, contact sports, airplane, public transport, concert, religious events, cinema/theater, attending a sporting event.
The higher the level of risk, the more important the measures to prevent the spread must be; all measurements and not just the mask. This helps to understand the different recommendations and measures imposed or proposed by public health officials.
In summary, the mask is useful, but if you are in a closed area for a long time, near an infected person, it may not be enough to keep you from catching it. So even if you wear a mask, you have to use it well and keep the idea of being in risky situations as short as possible.
In closing, the risk that each person is willing to take is theirs, as long as this does not alter the level of risk they impose on other people through their actions. Be understanding even if you don’t like certain situations.
Hopefully this situation will not last much longer.
- Bartoszko JJ, Farooqi MAM, Alhazzani W, Loeb M. Medical masks vs N95 respirators for preventing COVID-19 in healthcare workers: A systematic review and meta-analysis of randomized trials. Influenza Other Respir Viruses. 2020;14(4):365-373. doi:10.1111/irv.12745
- Bielecki M, Züst R, Siegrist D et al. Social distancing alters the clinical course of COVID-19 in young adults: A comparative cohort study. Clinical Infectious Diseases, 29 juin 2020.
- Chu DK, Akl EA, Duda S, et al. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. 2020;395(10242):1973-1987. doi:10.1016/S0140-6736(20)31142-9
- COVID-19 : point épidémiologique du 9 juillet 2020, Santé Publique France.
- Ezekiel J. Emanuel, MD, PhD Perelman School of Medicine at the University of Pennsylvania / James P. Phillips, MD, EMT-T George Washington University / Saskia Popescu, PhD, MPH University of Arizona/George Mason University. www.covid19reopen.com. 2020. COVID-19 Activity Risk Levels. Consulté le 24 juillet 2020.
- Kissler SM, Tedijanto C, Goldstein E et al. Projecting the transmission dynamics of SARS-CoV-2 through the postpandemic period. Science, 14 avril 2020.
- MacIntyre CR, Chughtai AA. A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients. Int J Nurs Stud. 2020;108:103629. doi:10.1016/j.ijnurstu.2020.103629
- Seow J, Graham C, Merrick B et al. Longitudinal evaluation and decline of antibody responses in SARS-CoV-2 infection. medRxiv, 11 juillet 2020.
- Stadlbauer D, Tan J, Jiang K et al. Seroconversion of a city: Longitudinal monitoring of SARS-CoV-2 seroprevalence in New York City. medRxiv, 29 juin 2020.
- ASSOCIATION OF INITIAL VIRAL LOAD IN SARS-CoV-2 PATIENTS WITH OUTCOME AND SYMPTOMS. The American Journal of Patholology DOI : 10.1016/j.ajpath.2020.07.001