A new study has found that “Airborne transmission of COVID-19 represents the dominant route for infection” and “wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission”.
These are conclusions from a study done by the PNAS (The Proceedings of the National Academy of Sciences of the USA), published June 16th. The combination of airborne transmission plus asymptomatic carriers is a recipe for an epidemic that is difficult to control. And that’s what we’re seeing.
Asymptomatic spread
We now know that there is a high rate of viral spread through asymptomatic carriers—people with no symptoms. Estimates vary from 25% to over 50% of cases originating from those who never get symptoms or have not yet started to show symptoms like fever and cough.
Airborne transmission
And, while 2 meters (6 feet) is known to greatly reduce virus transmission, other factors like air currents, temperature and humidity, can affect the length of time viral droplets and mists remain in the air and are able to infect those who inhale them. This makes it possible to transmit the virus in some situations even when physical distancing is maintained, and hands are washed properly. And we’ve all been in situations when you can’t keep even 1 meter (3 feet) distance.
Enter the mask…
This new study calculates that thousands of cases have been prevented in cities and countries where governments have mandated masks must be worn in public places. By examining changes in the rates of new infections after masks were mandated to be worn by everyone in public, the researchers estimate that over 78,000 infections were prevented by masks in Italy and over 66,000 in New York City from April 17th to May 9th.
The study looked at rates of new infection in various countries, and how the rates changed as they implemented various measures, as a way to scientifically determine the effectiveness of different strategies. While some countries, like China, mandated lock-downs, hand hygiene and wearing masks all at the same time, other countries made these changes separately, allowing researchers to determine the effect of each measure.
By analyzing the changes in the curve of disease cases when each new strategy was started in Wuhan, China, Italy and New York City between January 23rd and May 9th, they were able to illustrate the impact of each measure. The study showed that, while physical distancing made a small difference, the change was greater when masks were mandated to be worn by everyone when in public.
The reduction in new cases of COVID-19 when masks were mandated is clearly visible on graphs—with a “flattening of the curve” easily seen. This contrasts with the rest of the world where physical distancing, quarantine and isolation continued to be used alone. Here is one of the graphs… the circled dots show when masks were mandated to be worn in public in Italy and New York City:
You can see that the curve of the pink line representing NYC doesn’t change significantly as it crosses the 2 lighter blue lines representing social distancing and stay-at-home orders, but it drops noticeably after the circled dot marking the mandating of masks in public.
Researchers concluded that “wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with simultaneous social distancing, quarantine and contact tracing, represents the most likely fighting opportunity to stop the COVID-19 pandemic.” They also stated, “Other mitigation measures…are insufficient by themselves in protecting the public.”
Virus behaviour
We now know the main way of passing the coronavirus is breathing in air after an infected person has exhaled. Because of the high rate of asymptomatic transmission, chances are, this person wouldn’t even know they were infected. Washing your hands won’t prevent you from inhaling infected droplets. But masks can. This virus likes to hang out in the nose (as compared to SARS and MERS that preferred to stay in the lungs) so it is more likely to be breathed or coughed out that those previous similar infections. Shouting, singing, and even talking loudly can send a mist of tiny viral droplets into the air, some as an aerosol that can linger for much longer than suspected initially. Hand washing can protect you from virus in larger droplets that have settled on surfaces, and physical distancing reduces the number of particles that reach you, but masks are needed to prevent those who are sick but not diagnosed from unknowingly creating a contaminated aerosol mist that others can inhale.
World Health Organization (WHO)
However, the World Health Organization (WHO) insists that “masks alone are not a replacement for physical distancing, hand hygiene, and other public health measures.” But, they say, cloth masks may provide a “modest reduction in transmission” by:
· “reducing the risk of asymptomatic carriers spreading the virus”
· “reminding the population that the pandemic is ongoing and everyone can play a role in stopping it” as well as
· Stimulating the economy by “encouraging the public to create their own masks.”
They also suggest there are disadvantages to cloth masks worn by the public:
· Touching the mask too often (usually due to a poor fit)
· Potential to cause headaches, breathing difficulties or skin irritations and
· The possibility of creating a “false sense of security” as they are not 100% protective
Note that these disadvantages are not supported by objective research. I find it odd that a high level of proof is required to recommend a measure, but they readily share disadvantages with no objective studies. I can’t help wondering why they are so hesitant to recommend a safe measure like masks, especially now that plenty of supporting science is emerging for this strategy. You can read or listen to more about reasons to wear or not wear a mask in my blog “Masks 4 All” (Blog or audio track).
And this week (to add to the confusion) the WHO stated there was no evidence of asymptomatic virus spread, despite many studies that found this is a major problem with COVID-19. They later explained that they were referring to non-symptomatic people who never showed symptoms but had had a positive test, not those who were pre-symptomatic and developed symptoms within a day or two. Pre-symptomatic people are known to be highly infectious. There are plenty of examples of “super spread” events involving infected individuals who progressed to symptoms soon afterward.
This certainly demonstrates the importance of clear communication. As one friend said, whatever they tell us today will probably change by next week. Confusing messages create mistrust of advice from authorities and result in fewer people following recommendations to limit viral spread. We are seeing this especially in increased numbers of infections in young people in their teens and 20s.
Meanwhile, the WHO reported the highest number of new cases yet on June 8th, bringing the global total to 8 million, and they stated that the pandemic is worsening. We need to continue physical distancing, hand washing, and staying at home as much as possible. And there’s enough evidence now to know that adding a mask whenever we cannot stay away from others will further reduce new cases. It’s so easy to become complacent… but we’re not out of the woods yet. In fact, you could say we’re still in the middle of the forest!
In Canada…
In Canada, British Columbia and New Brunswick (my province!) are leading the way with good control and low numbers of cases. Experts attribute this to:
· strong leadership with clear communication and quick decision-making,
· better data transparency with open reporting of cases and
· a high level of cooperation by the public. New Brunswick’s mainly rural population is also believed to be a helpful factor.
So, why do I keep talking about masks?
I feel compelled to keep talking about masks when I read they work but still see how few people in my community wear them. While reports suggest there are very few cases in our area, it’s only a matter of time until one arrives here, as happened recently in northern NB, and without masks the virus can quickly spread until it’s detected and those affected are traced and isolated. It’s even more important in urban areas with higher population density.
Governments are too often slow to respond, but the evidence is clear now. If at least 80% of people wear masks when in public places, the pandemic can be controlled. If you can’t wear a mask for health reasons, it’s OK as long as the people around you wear one. If you dislike wearing a mask or can’t wear one, minimize your time in public places—and just stay home. That works too! But, most of us need to do our part and find some type of face covering we are comfortable wearing, if we want to stop the spread of COVID-19.
So, what’s your favourite type of mask? Are you able to adjust it properly so it feels comfortable? I keep searching for the perfect design…
References:
Identifying airborne transmission as the dominant route for the spread of COVID-19 – PNAS
A modelling framework to assess the likely effectiveness of facemasks in combination with ‘lock-down’ in managing the COVID-19 pandemic – Proceedings of the Royal Society
Geography, leadership and sheer luck: Why BC and NB flattened the curve so quickly – CTV News
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