Watch: How do masks and ventilation prevent COVID-19 transmission?

Musicians wearing face masks or behind screens due COVID-19 protocol measures rehearse at the Teatro Real in Madrid, Spain.
Musicians wearing face masks or behind screens due COVID-19 protocol measures rehearse at the Teatro Real in Madrid, Spain. Copyright AP Photo/Bernat Armangue
By Danielle OlavarioLauren Chadwick
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A new estimation tool attempts to predict how many people could become infected with COVID-19 in different indoor scenarios.


With the COVID-19 pandemic upending our lives, many would like to measure the personal risks they take under different scenarios.

Already, scientists agree that the novel coronavirus is spread through droplets but can also linger in the air, especially in poorly ventilated spaces.

That’s why some researchers are trying to measure how masks and ventilation can contribute to preventing infection.

Jose-Luis Jimenez is an atmospheric chemist at the University of Colorado Boulder and he created an infection risk estimator based on the most recently available information about the spread of COVID-19.

The expert in the dynamics of particles in the air uses two known models based on the dispersion of contaminants and how people are infected by airborne viruses to determine the number of people who would be infected in certain settings.

“The model tries to simulate the conditions that lead to superspreading. It is calibrated with real superspreading events of this disease, such as the Skagit choir in the US, the restaurant and bus cases in China etc. So we expect that it'll give useful estimates when a superspreader is present in an indoor space,” Jimenez told Euronews.

According to the model, if six people were in a room without masks and with poor ventilation for four hours and one person was positive for COVID-19, everyone would become infected.

However, if we reduce the amount of time to two hours and everyone wears masks and there is good ventilation, just one other person becomes infected.

Watch how the model works in the video player above.

But there are outlying questions that make it difficult to predict how the contagion could act in a room, including that scientists still do not fully understand how contagious certain people are.

The model does appear to show however the importance of good ventilation and mask-wearing in the fight against COVID-19 -- but it also shows the limits.

“I see this as helping us generate a ‘riskiness’ ranking based on the physics, but the actual epidemiological outcomes are always trickier to predict,” said Natalie Dean, a professor of biostatistics at the University of Florida, pointing out that it can be difficult to predict how someone is infected.

Dr Emma Hodcroft at the University of Bern said that she's a "big advocate" about "talking a lot more about aerosols and their role in infection" explaining those aspects are "greatly overlooked".

"It's pretty easy to wipe down tables and surfaces, space things out [2 metres] apart, and feel safer without impacting how a business or location works -- but it's harder to ventilate, mandate masks, reduce density and reduce time in a location -- that fundamentally changes businesses and how they work," Hodcroft told Euronews.

Experts agree that mask-wearing and good ventilation are key to bringing down infections.

“Mask use is by no means a panacea and needs to be done in combination with other measures,” said Hans Kluge, the World Health Organization’s regional director for Europe.

“However, if mask use reached 95%, ‘lockdowns’ would not be needed. But, at 60% or lower masks use, it is hard to avoid lockdowns.”

A June 2020 study published in Health Affairs found that masks do slow the spread of COVID-19 after an analysis of mask mandates in fifteen US states and Washington DC.


There has also been anecdotal evidence of their effectiveness.

In Missouri, two hairstylists with COVID-19 came into contact with 140 clients and none of them contracted the virus.

Jimenez’s tool also measures the importance of good ventilation to combat COVID-19.

The US Centres for Disease Control and Prevention (CDC) warns that airborne transmission of COVID-19 can occur in poorly ventilated settings but says that spread is "primarily through respiratory droplet transmission within a short-range".

"There is no evidence of efficient spread (i.e., routine, rapid spread) to people far away or who enter a space hours after an infectious person was there," the CDC says.


But "inadequate ventilation" can create "a build-up of suspended small respiratory droplets and particles", the CDC adds.

The World Health Organization has also recognised a risk of airborne transmission spread in places with poor ventilation, in a report that came following a letter of 239 experts urging scientists to recognise the possibility.

Many health authorities now suggest opening windows if inside or meeting outside if possible to avoid indoor gatherings where people risk more easily spreading coronavirus.

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