Face masks essential in combating asymptomatic spread of SARS-CoV-2 aerosols and droplets

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The coronavirus disease (COVID-19) occurs through the transmission of droplets and aerosols from infected people through speaking, breathing, coughing, and sneezing. Wearing masks can reduce the airborne transmission of the novel coronavirus, a new study finds. The research is published in the journal Science.

The team of researchers at the University of California San Diego and the National Sun Yat-sen University in Kaohsiung, Taiwan, identified that wearing masks is essential to combat the asymptomatic spread of aerosols and droplets.

Asymptomatic carriers make up the bulk of those who transmit the virus. They are the ones who are infected but do not manifest any symptom, making it hard to contain the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

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Jenny Harries, the UK's deputy chief medical officer, said masks could “actually trap the virus”. Image Credit: Robert Wei / Shutterstock

How does the coronavirus spread?

The SARS-CoV-2 spreads primarily through droplets of saliva or nasal discharge when an infected person coughs or sneezes, the World Health Organization (WHO) reports. Growing evidence suggests that SARS-CoV-2, which causes COVID-19, can be spread by asymptomatic people via aerosols.

The researchers said that a large proportion of the virus spread appears to be happening through the airborne transmission of aerosols or airborne particles produced by asymptomatic carriers during speaking and breathing.

The airborne spread of the virus from people who are not aware they are infected highlights the importance of mass testing, wearing masks, and physical distancing to reduce the spread of the virus.

Using masks to prevent virus spread

When dispersed in the air, aerosols can accumulate and remain infectious in indoor air for hours. The particles are so small that they are easily inhaled into the lungs.

The droplets produced by humans can range between 0.1 and 1000 μm. Many factors can influence how far emitted droplets and aerosols will travel in the air, including gravity, inertia, droplet size, and evaporation.

Some droplets, because of their size, may contaminate surfaces and lead to contact transmission. Smaller droplets will evaporate faster than they settle and can stay in the air.

One recent study estimated that a single minute of loud-speaking might generate between 1,000 to 100,000 virion-containing aerosols or virus particles suspended in the air. The aerosols can accumulate indoor and in uncirculated air for hours, where they can be inhaled deeply into the lungs.

Masks are effective in reducing the airborne transmission of SARS-CoV-2. Properly fitted masks provide an effective physical barrier to reduce the number of viruses in the exhaled breath of asymptomatic carriers or the “silent shedders.”

“Infectious aerosol particles can be released during breathing and speaking by asymptomatic infected individuals. No masking maximizes exposure, whereas universal masking results in the least exposure,” the researchers explained.

The researchers also noted that the countries that were successful in reducing virus spread had implemented universal masking,

“From epidemiological data, countries that have been most effective in reducing the spread of COVID-19 have implemented universal masking, including Taiwan, Hong Kong, Singapore, and South Korea,” the researchers said.

Further, they added that people should wear masks in areas with conditions that can accumulate high concentrations of viruses, such as airplanes, restaurants, health care settings, supermarkets, and other crowded places.

The U.S. Centers for Disease Control and Prevention (CDC)recommends wearing cloth face coverings in public settings where other social distancing measures are hard to maintain, including pharmacies and grocery stores.

Further, surgical masks and N95 masks should be given priority to front-liners such as healthcare workers, given the scarcity of their supply.

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Others:

World Health Organization (WHO). (2020). Coronavirus. https://www.who.int/health-topics/coronavirus#tab=tab_1

U.S. Centers for Disease Control and Prevention. (2020). Recommendation Regarding the Use of Cloth Face Coverings, Especially in Areas of Significant Community-Based Transmission. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/cloth-face-cover.html

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