Cloth Masks Highly Effective Covid Prevention For Wearer, Others says, US Health Body

 CDC says multi layered cloth masks can block up to 50-70% of aerosols, blocks most large droplets and helps reduce inhalation of those droplets by the wearer.

Image Source: Google

World News/Covid-19 outbreak: A cloth mask protects not just others but also the wearer from the SARS-CoV-2 virus, per the US Centres for Disease Control (CDC).

In a new brief issued Tuesday, the CDC recommended wearing non-valved multi-layer cloth masks to stop transmission of Covid-19. It noted that masks prevent transmission of the virus by pre-symptomatic and asymptomatic individuals and also helps reduce inhalation of those droplets by the wearer.

“The community benefit of masking for SARS-CoV-2 control is due to the combination of these effects; individual prevention benefit increases with increasing numbers of people using masks consistently and correctly,” the CDC said during a statement.

This is a move far from the body’s earlier stand that masks are intended to reduce the emission of virus-laden droplets only from infected wearers who may be asymptomatic.

The SARS-CoV-2 virus is transmitted predominately by respiratory droplets generated when people cough, sneeze, sing, talk or breathe.

According to the CDC, cloth masks not only effectively block most large droplets, but may also block the exhalation of fine aerosols. Multi-layer cloth masks can block up to 50-70 per cent of aerosols and also limits the forward spread of these that aren't captured.

In its statement, the US health body cited several studies to notice that over 80 per cent of all respiratory droplets were blocked with cloth masks. In some studies, the cloth masks performed on par with surgical masks.

‘Universal masking may avert future lockdowns’

While the effectiveness of various masks has varied widely across studies, multiple layers of cloth with higher thread counts have demonstrated superior performance compared to a single layer of cloth with lower thread counts.

Some materials like polypropylene may enhance filtering effectiveness by generating a sort of static electricity, while silk may help repel moisture droplets — maintaining breathability and comfort, noted the CDC.

The statement also referred to a study of a high-exposure event, where 2 Covid-19 positive hair stylists interacted for an average of 15 minutes with about 139 clients during an eight-day period. However, none of the 67 clients, who subsequently consented to an interview and testing, were infected.

The stylists and clients universally wore masks in the salon as required by local ordinance and company policy at the time.

In another study of 124 households in Beijing with but one case of Covid-19, mask use by the patient and family contacts before the patient developed symptoms reduced secondary transmission within the households by 79 per cent.

“Adopting universal masking policies can help avert future lockdowns, especially if combined with other non-pharmaceutical interventions such as social distancing, hand hygiene, and adequate ventilation,” CDC said in its statement.

ALSO READ|

India’s Serum says produced 40 million doses of AstraZeneca COVID-19 vaccine

Pfizer says COVID-19 vaccine over 90% effective

New Visualization shows face shields and mask with valves may not protect against COVID-19 spread properly

Small droplets can easily move round the sides of the visor, the study found.

(Image credit: Siddhartha Verma, Manhar Dhanak, John Frankenfield)

A new visualization shows why face shields and masks with exhalation valves might not be the simplest barriers for preventing the spread of COVID-19.

Although face shields initially block droplets from a simulated cough, small droplets can easily move round the sides of the visor and eventually cover an outsized area, consistent with the visualization, which is detailed during a study published Tuesday (Sept. 1) within the journal Physics of Fluids.

For masks with exhalation valves, a stream of droplets passes, unfiltered, through the valve, meaning the mask would in theory do little to hinder the spread of potentially infectious droplets. 

In contrast, the researchers previously showed that some cotton face masks reduce the spread of droplets to only a couple of inches from the face during a simulated cough.

The simulations within the new study "indicate that face shields and masks with exhale valves may not be as effective as regular face masks in restricting the spread of aerosolized droplets," the authors wrote. 

Face masks became a part of lifestyle during the COVID-19 pandemic. But some people are turning to plastic face shields or masks with exhalation values because they find these alternatives easier to wear for long periods of your time . Face shields even have the advantage of allowing users to point out facial expressions.

However, the Centers for Disease Control and Prevention (CDC) doesn't recommend either of those as alternatives to cloth masks. Masks with one-way valves, which are intended to be used in construction work, allow users to inhale filtered air and exhale warm, moist (and unfiltered) air through the valve. But because respiratory droplets from the wearer are expelled into the air, the CDC says people shouldn't wear these masks to stop COVID-19 spread.

The CDC also doesn't recommend face shields as a substitute for cloth masks because evidence is lacking to point out their effectiveness, the agency says.

"As students return to schools and universities, some have wondered if it is better to use face shields, as they are more comfortable and easier to wear for longer periods of time," study lead author Siddhartha Verma, an professor at Florida Atlantic University's College of Engineering and computing , said during a statement. "But what if these shields are not as effective? you would be essentially putting everyone in a tight space with droplets accumulating over time, which could potentially lead to infections."

In the new study, the researchers simulated coughing by connecting a mannequin's head to a fog machine — which creates a vapor from water and glycerin — and using a pump to expel the vapor through the mannequin's mouth. They then visualized the vapor droplets using a "laser sheet" created by passing a green laser pointer through a cylindrical rod. during this setup, simulated cough droplets appear as a glowing green vapor flowing from the mannequin's mouth.

For the face shield simulation, the shield initially deflected droplets toward the bottom after a cough. But small droplets remained suspended at rock bottom of the shield then floated round the sides, eventually spreading about 3 feet (0.9 meters) to the front and sides of the mannequin. In some cases, the droplets spread backward, behind the mannequin, rather than forward.

For the mask with a valve, a jet of droplets skilled the valve within the front of the masks during coughing. Initially, this jet of droplets traveled toward the bottom , but eventually the droplets dispersed over a good area.

The researchers also tested two different brands of commercially available surgical masks. Both of those masks weren't recommended for medical use by the manufacturers. Although the masks looked similar, one brand was effective at stopping the forward spread of aerosolized droplets, while the opposite allowed a high number of droplets to leak through the mask. 

"This indicates that even among commercially available masks which may appear to be similar superficially, there can be significant underlying differences in the quality and type of materials used for manufacturing the masks," the authors said.

Since the study was a simulation, it doesn't provide data on the exact conditions that might end in the spread of an infection. for instance , with SARS-CoV-2, the virus that causes COVID-19, it's unclear exactly how long the virus remains infectious within the air, and the way far infectious particles can travel, or what proportion virus is required to make an individual sick.

The authors also noted that "even the very best masks have some degree of leakage," Verma said. So "it's still important to maintain physical distance while wearing [masks] to mitigate transmission." 

Also Read |

Japan's 'flying car' gets off ground, with a person aboard