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Aerosols the main route of COVID-19 transmission, says WHO. NSYSU ASRC: only a well-fitting mask can effectively filtrate aerosols


World Health Organization (WHO) has recently confirmed that aerosols are the main route of transmission of COVID-19 and the United States Centers for Disease Control and Prevention will change their epidemic prevention policy accordingly. With local infection cases quickly spreading in Taiwan in the past few days, Director of Aerosol Science Research Center Chia C. Wang called on the citizens to stay alert. She emphasized that according to the newest paper by German researchers, how well-fitting the mask is, greatly influences its aerosol filtration efficiency. For example, for particles with a diameter equal to or below 2.5 µm, the filtration efficiency decreases by 50% for a leak of 1% of the sample area.

Aerosols are fine liquid droplets or solid particles suspended in the air. People release aerosols of diameter below 5 µm when they speak, sing, cough, and simply breathe. People infected with COVID-19 release virus-laden aerosols into the environment via these expiratory activities.

Director Wang pointed out that as the pandemic is worsening around the world, more and more research results get published in different fields, including air sampling analysis, epidemiological statistics, clinical and animal tests, and aerodynamic simulation. This has pushed WHO to officially recognize aerosol transmission as the main route of COVID-19 transmission on April 30. Since the outbreak of the epidemic, there have been numerous superspreading events pointing to aerosol transmission as the main route. Previously, there was a cluster infection in a quarantine hotel in New Zealand, and the investigation found that aerosols were the main route of transmission. In other countries, there has also been a number of cases of healthcare workers becoming infected despite maintaining social distance and wearing masks, and this was also attributed to aerosols. Recently, there have been a few cluster infections in Taiwan, which greatly increased the risk of community transmission.

Director Wang said that when asymptomatic individuals unaware of their infection status don’t wear a mask nor implement any preventive measures, aerosols become the main route of transmission. Studies have shown that a high proportion of COVID-19 patients are asymptomatic or have only mild symptoms at the time of diagnosis and that more than 50% of COVID-19 transmissions occur when the individual is asymptomatic. With the epidemic becoming serious in Taiwan, she reminded the public to stay vigilant and pay particular attention to wearing well-fitting face masks. "Make sure you wear it properly."

“Before, people would believe that the spread of aerosols could only occur at a certain distance, but ignored the fact that the concentration of aerosol particles is actually higher the closer you are to the source of infection, and thus, the chance of infection is greater.” Director Wang said that recent studies by overseas researchers have shown that N95, medical masks, and cotton masks are the most effective in filtering out SARS-CoV-2, with N95 masks being the most effective of all three. However, other masks also have certain filtration efficiency and offer protection. Besides, the research team of Max Planck Institute in Germany tested the efficiency of different masks in filtering particles of different sizes and found that with a leak of 1% of the sample area, the filtration efficiency for particles of a diameter equal or below 10 µm is still nearly 70%, but only 50% for 2.5 µm particles. With a leak of 2%, the filtration efficiency for 2.5 µm particles is only 13% of the perfectly fitting mask. In addition to abiding by the existing preventive measures, Director Wang reminded the public to wear a well-fitting mask, install a high-efficiency air filter and UVC air sterilizer, and avoid crowded areas with poor ventilation to reduce the risk of infection by aerosol transmission.


In February 2020, long before the epidemic spread to the present scale, Director of Aerosol Science Research Center Chia C. Wang published a column warning readers to stay alert about the new virus and in May 2020, released a perspective article in Science, a top international journal, stating that SARS-CoV-2 virus causing COVID-19 disease can be transmitted in the air in the form of aerosols and droplets. Unlike larger droplets that are grounded within seconds by the force of gravity, aerosols can float in the air for hours or longer, dragged by the air. A droplet with a diameter of 100 µm needs only 5 seconds to fall to the ground from a height of 1.5 m (the average height of adults’ nose and mouth), while a droplet of 1 µm needs 12.2 hours to fall to the ground from the same height. Although the infectivity of the virus gradually decreases over time, if one ingests a virus-laden aerosol still contagious into the respiratory tract or lungs, this will allow the virus to replicate in a new host and cause an infection.

Aerosol Science Research Center is the first and only aerosol-themed center in Asia. In recent years, it has been committed to research in PM 2.5-preventive medicine, aerosol biomedicine research, diseases caused by PM 2.5, such as respiratory and pulmonary diseases, cardiovascular diseases, children's cognitive development disorders, paving the important foundation for the PM 2.5 preventive medicine. Bioaerosols, such as viruses, bacteria, and other biogenic pathogens suspended in the air, the related pathogenesis, prevention, and medical strategies, is now one of the research focuses of ASRC, aiming at bringing innovation to medicine and improving people’s quality of life and well-being.

Reference material:

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