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HomeCoronavirus WatchMost blue surgical masks ineffective against COVID-19 — Canada study

Most blue surgical masks ineffective against COVID-19 — Canada study

Most blue surgical face masks used by many during the pandemic are not enough to avoid people from being infected with COVID-19, a Canadian study found. Even modest ventilation rates were found to provide about the same level of protection as the highest quality masks, the lead author noted.

The study from the University of Waterloo in Canada showed N95 or KN95 masks did the best job in containing aerosol droplets from the wearer's mouth.

The blue cloth surgical masks that have become popular during the pandemic were found to filter only 10% of aerosol droplets, as they do not cover the face properly.

“There is no question it is beneficial to wear any face covering, both for protection in close proximity and at a distance in a room,” said study leader Serhiy Yarusevych, a professor of mechanical and mechatronics engineering. “However, there is a very serious difference in the effectiveness of different masks when it comes to controlling aerosols.”

Yarusevych and team said that many people wear masks that don't fit their faces properly, unlike the N95, which straps itself tightly around the wearer. This causes aerosol droplets to escape through multiple openings between a person's face and the cloth mask, which could spread COVID-19 in populous areas.

The N95, on the other hand, filtered more than 50% of aerosol droplets while the other half is dispersed above the wearer's head.

“A lot of this may seem like common sense,” added Yarusevych. “There is a reason, for instance, why medical practitioners wear N95 masks – they work much better. The novelty here is that we have provided solid numbers and rigorous analysis to support that assumption.” Even modest ventilation rates were found to provide about the same level of protection as the highest quality masks, Yaruservch said.

The Daily Mail reports that earlier this month, President Joe Biden's former COVID-19 advisor and top epidemiologist warned Americans “that many of the face cloth coverings that people wear are not very effective”. Michael Osterholm said people need to wear N95 respirators that were more effective against COVID-19, adding that he disliked the term ‘masking’ as it suggested any face covering would protect from the spread of COVID-19, which is not accurate

“We're in a very unfortunate situation … we've really brought this country to a point of confusion that really misses the main point that we should be focusing on vaccine, vaccine, vaccine," said Osterholm, who is the director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

Regarding the term 'masking', he said: “It implies that anything you put in front of your face works and if I could just add a nuance to that, which hopefully doesn't add more confusion, it's that we know many of the face cloth coverings that people wear are not very effective in reducing any of the virus movement, in or out.”

The Centre for Disease Control & Infection has been criticised for its confusing stance on masks after it reversed its mask guidelines. But cities and states say they need to see the evidence before revising their own policies.

Federal officials say unpublished data showed vaccinated people infected with COVID-19 may be able to transmit the virus, leading them to recommend that everyone should wear a mask indoors in areas of high transmission.

Texas and Florida have championed mandates banning mask requirements in the classroom, added Daily Mail, but on Friday, the Supreme Court of Texas rejected Governor Greg Abbott's latest bid to scrap mask mandates.

Abbott, who tested positive for the virus on Tuesday, is leading the anti- mask charge along with his Republican colleague, Florida Governor Ron DeSantis. Texas confirmed nearly 19,000 new cases by Saturday, with 190 new deaths, according to the Texas Department of State Health Service. Florida reported more than 150,000 new cases for the week and nearly 1,500 new deaths.

Last Wednesday, US health officials announced plans to dispense booster shots to all Americans to shore up their protection amid the surging delta variant and signs that the vaccinesʼ effectiveness was slipping.

Study details

Experimental investigation of indoor aerosol dispersion and accumulation in the context of COVID-19: Effects of masks and ventilation
Yash Shah, John W. Kurelek, Sean D. Peterson, Serhiy Yarusevyc

Published in Physics of Fluids 21 July 2021

Abstract

The ongoing COVID-19 pandemic has highlighted the importance of aerosol dispersion in disease transmission in indoor environments. The present study experimentally investigates the dispersion and build-up of an exhaled aerosol modeled with polydisperse microscopic particles (approximately 1 μm mean diameter) by a seated manikin in a relatively large indoor environment.

The aims are to offer quantitative insight into the effect of common face masks and ventilation/air purification, and to provide relevant experimental metrics for modeling and risk assessment. Measurements demonstrate that all tested masks provide protection in the immediate vicinity of the host primarily through the redirection and reduction of expiratory momentum.

However, leakages are observed to result in notable decreases in mask efficiency relative to the ideal filtration efficiency of the mask material, even in the case of high-efficiency masks, such as the R95 or KN95. Tests conducted in the far field (2m distance from the subject) capture significant aerosol build-up in the indoor space over a long duration (10 hours).

A quantitative measure of apparent exhalation filtration efficiency is provided based on experimental data assimilation to a simplified model. The results demonstrate that the apparent exhalation filtration efficiency is significantly lower than the ideal filtration efficiency of the mask material. Nevertheless, high-efficiency masks, such as the KN95, still offer substantially higher apparent filtration efficiencies (60% and 46% for R95 and KN95 masks, respectively) than the more commonly used cloth (10%) and surgical masks (12%), and therefore are still the recommended choice in mitigating airborne disease transmission indoors

The results also suggest that, while higher ventilation capacities are required to fully mitigate aerosol build-up, even relatively low air-change rates (2h−12 h−1) lead to lower aerosol build-up compared to the best performing mask in an unventilated space.

 

Daily Mail article – Blue surgical face masks are only 10% effective in preventing COVID infection, new study finds (Open access)

 

Physics of Fluids article – Experimental investigation of indoor aerosol dispersion and accumulation in the context of COVID-19: Effects of masks and ventilation (Open access)

 

See more from MedicalBrief archives:

 

12 tested KN95 mask brands used in SA fail international safety standards — UCT study

 

Public use of surgical masks 'could help slow' COVID-19 pandemic's advance

 

CDC Guidelines: Maximising fit for cloth and medical procedure masks

 

Mask wearing effectiveness, including among asymptomatic COVID-19 carriers

 

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