It’s Not Just COVID-19: Most Respiratory Viruses Actually Spread by Aerosols

SARS-CoV-2, the virus behind today’s global coronavirus pandemic, spreads primarily by inhalation of virus-laden aerosols at both short and long ranges — and a comprehensive new assessment of respiratory viruses finds that many others probably do as well. SARS-CoV, MERS-CoV, influenza, measles, and the rhinoviruses that cause the common cold can all spread via aerosols that can build up in indoor air and linger for hours, an international, interdisciplinary team of researchers has reported in a review published in Science on August 27, 2021.

Over the last century and at the beginning of this pandemic, it was widely believed that respiratory viruses, including SARS-CoV-2, mainly spread through droplets produced in coughs and sneezes of infected individuals or through touching contaminated surfaces. However, droplet and fomite transmission of SARS-CoV-2 fails to account for the numerous superspreading events observed during the COVID-19 pandemic, or the much higher transmission that occurs indoors versus outdoors.,49266973.html

Motivated by a desire to understand the factors leading to the COVID-19 pandemic, the researchers from Taiwan, the United States, and Israel sought to identify as clearly as possible how the coronavirus and other respiratory viruses spread. For example, the team reviewed numerous studies of superspreading events observed during the COVID pandemic, and found the studies consistently showed that airborne transmission is the most likely transmission route, not surface contacts or contact with large droplets. One common factor at these superspreading events was the shared air people inhaled in the same room.

Many were linked to crowded locations, exposure durations of one hour or more, poor ventilation, vocalization, and lack of properly worn masks. The researchers also reviewed evidence collected from many other types of studies—air sampling, polymerase chain reaction (PCR)-based and/or cell culture studies, epidemiological analysis, laboratory and clinical studies, and modeling work—and concluded that airborne transmission is a major, or even dominant transmission pathway for most respiratory diseases, not just COVID-19.

Rendering of mutating virus cells. Credit:

 “Transmission through inhalation of virus-laden aerosols has been long underappreciated. It is time to revise the conventional paradigms by implementing aerosol precautions to protect the public against this transmission route,” said Chia C. Wang, director of the Aerosol Science Research Center and an aerosol physical chemist at National Sun Yat-sen University, Taiwan, who led the review.

Prevailing paradigms about respiratory disease transmission date back as much as a century, the team noted. Airborne transmission was paternalistically dismissed in the early 1900s by prominent public health figure Charles Chapin due to a concern that mentioning transmission by air would scare people into inaction and displace hygiene practices. An unsupported assumption that erroneously equated infections at close range with droplet transmission has shaped the current paradigm for controlling respiratory virus transmission. However, “this assumption neglects the fact that aerosol transmission also occurs at short distances, because the concentration of exhaled aerosols is higher when one is closer to the infected person emitting them,” said Kim Prather, director of the National Science Foundation Center for Aerosol Impacts on Chemistry of the Environment at UC San Diego’s Scripps Institution of Oceanography at UC San Diego and an aerosol chemist who co-led the review.

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