Why is it important to wear a mask?
To understand the importance of wearing a mask, we need to know how the SARS-CoV-2, the virus that causes COVID-19, spreads. Research has now shown that environmentally mediated transmission via contamination (this means, transmission by touching contaminated objects in the environment) accounts only for 6% of COVID-19 infections. The majority of spreads through respiratory droplets emitted by infected people when they talk, cough, sneeze or merely exhale. These droplets are subsequently breathed in by other people nearby. This is the underlying reason why physical distancing is so essential.
By now, I am confident that we have all now learned about the two-metre rule for preventing the transfer of virus-containing droplets. It is also important to note that a sneeze or cough can expel the contagious droplets to as far as 7 to 8 metres. What is more alarming is perhaps, the fact that these microdroplets can linger in the environment for quite some time as shown in the experiments conducted by the researchers from St. Marianna University - School of Medicine, Japan. NHK World Japan documented the experiment in the video shown on YouTube.
It is also useful to know the term "reproductive ratio" (R0) that is used to describe the infectiousness of a virus. A disease like measles has an R0 of 18, which means that a person who has measles can potentially infect 18 other people in close vicinity. You may think that COVID-19 would have an R0 with a number a lot higher than 18, but surprisingly, it is not. In fact, COVID-19 has an average R0 of 2 to 3 which implies that a person who is positive, can probably infect, on average, two or three others while doing his/her daily routines. Not to downplay the small number, an R0 of 2 is more than sufficient to cause a global pandemic.
Another factor to consider is exposure time. At this point, it is not yet known the exact exposure time needed to infect someone. However, the US government agency for Centers for Disease Control and Prevention (CDC) has said that even if you are in the vicinity with an infected person, as long as the exposure time is less than 15 minutes, you are unlikely to get the COVID-19. The guideline seems to be formulated by active monitoring study of exposed patients with confirmed COVID-19. The study stated that out of 445 people who are within 2 metres for 10 minutes or more from the ten established COVID-19 patients, including 19 members of the patients' households, only two tested positive. While this study does bring us a certain degree of comfort, we must not let our guards down, because a single infected person who is not cared for promptly, can lead to thousands of infections.
The main problem of the SARS-CoV-2 virus (the virus that caused COVID-19) is that it can make people infectious even before they develop the symptoms of the illness. One research suggests that viral shedding may begin 2 to 3 days before the first onset of the symptoms. Another study from Taiwan corroborated the findings.
Based on the facts outlined above, it is therefore vital to couple social distancing with wearing a mask. The reasoning behind wearing a mask is that it will serve as a filter to block the respiratory droplets from an infectious person. But there are so many kinds of masks out there; which one should we use?
An article published in Nature Medicine journal reported that when worn appropriately with the right fit, surgical masks are very effective at blocking respiratory droplets containing influenza viruses and coronaviruses.
Surgical masks are made of nonwoven polypropylene fibre fabric by a melt-blowing process. The nonwoven fabric makes the masks more breathable when compared to woven materials such as homemade cloth masks. What makes the filtration process effective in blocking the respiratory droplets is not from the fabric itself, but from the electrostatic charge that is applied to the fabric. It is this static electricity that catches the respiratory droplets. The downside of using static electricity to intercept the respiratory droplets is that the mask cannot be washed or sterilised using alcohol. Using water and soap or alcohol to 'sterilise' the mask will destroy the electrostatic coating and renders the mask useless.
A surgical mask is designed to protect others rather than the wearer. The reason is that a surgical mask is not airtight at the sides, and so air can flow in and out freely.
Cloth masks are the most commonly worn in this pandemic. While it is not as effective as a surgical mask to keep the infections respiratory droplets in, it does the job well according to this research. Moreover, another study found that SARS-CoV-2 virus does not last long on cloth. In just three hours, there is over ninety per cent drop from the initial virus count.
Cloth mask is cheap and washable. Depending on the type of cloth chosen to make the mask, it can feel uncomfortable with prolonged use as it can get warm and suffocating, which is the reason why we see many people wearing the mask below their noses or taking it off.
Similar to a surgical mask, a cloth mask is purposed to protect others and rather than the wearer.
What is so special about the N95 mask is that it is designed to fit tightly on our face, surrounding our mouth and nose so that the air that we breathe comes through the mask entirely. Moreover, it uses a filter with a higher electrostatic charge compared to the surgical masks, which make it a very efficient filtration system. In fact, it blocks at least ninety five per cent of airborne particles as small as 0.3 microns. Our respiratory droplets are in the size of 1 to 10 microns, excluding aerosols.
The clear advantage of the N95 mask is that it protects the wearer as well as other people in the vicinity. Ideally, everyone should be wearing this mask, but we must prioritise the use of this mask for health care and front line workers where they need it the most. On the other hand, just like the surgical mask, it is intended for single use only. Washing or sanitising it with alcohol would render the electrostatic charge obsolete.
Wearing N95 for an extended time is also distinctly uncomfortable, even more than a surgical mask: it is warmer, harder to breathe, and it mutes your voice, making it difficult for others to hear you.
There is another kind of N95 mask that features a valve. This valve will allow exhaled air to flow out freely while providing protection for inhaled air. The problem with the N95 with a valve is that it exposes the people around the wearer to possible infection. Viruses that may be present in the wearer is exhaled fully, making it no different from a sick person not wearing a mask. Whenever possible, we should avoid wearing this mask unless there is no other choice.
The evidence benefits of wearing a mask amid the coronavirus pandemic are overwhelming as we have discussed above. If at least sixty per cent of the population wore masks that is sixty per cent efficient (a well-fitting two-layer cotton mask), then the chain of transmission can be stopped according to this study. The higher the percentage of the population wearing and the more effective are the masks worn, the faster this pandemic can end. We must, therefore, do our part to wear a mask when we are out of the house, and we must insist on the people around us to wear a mask as well. The four pillars of public health safety — hygiene, physical distancing, screening, and masks, can keep all of us safe while resuming some form of normalcy.
Photos can be found at Unsplash.