Growing evidence suggests that SARS-CoV-2, the novel coronavirus that causes COVID-19, can be spread by asymptomatic people via aerosols -- a reality that deeply underscores the ongoing importance of regular widespread testing, wearing masks and physical distancing to reduce the spread of the virus, say Kimberly Prather and colleagues in a new Perspective published in the journal Science.

The World Health Organization (WHO) recommendations for social distancing of 6 feet and hand washing to reduce the spread of SARS-CoV-2 are based on studies of respiratory droplets carried out in the 1930s. When these studies were conducted, the technology did not exist for detecting submicron aerosols. More recently, measurements show that intense coughs and sneezes that propel larger virus droplets more than 20 feet can also create thousands of aerosols that can travel even further. Recent studies of SARS-CoV-2 have shown that in addition to droplets, SARS-CoV-2 may also be transmitted through aerosols. One recent study estimated that a single minute of loud speaking might generate between 1,000-100,000 virion-containing aerosols or virus particles suspended in the air, for example. These infectious aerosols can accumulate in indoor, uncirculating air for hours, where they can be more easily inhaled deeply into the lungs. Given how little is known about the airborne behavior of infectious aerosols, it's difficult to define a safe distance for physical distancing, the authors say. Properly fitted masks provide a critical physical barrier, reducing the number of infectious viruses in the exhaled breath of asymptomatic individuals. Countries that have been most effective in limiting the spread of COVID-19 have implemented universal masking, they note. It is particularly important to wear masks in locations with conditions that can accumulate high concentrations of viruses, such as health care settings, airplanes, restaurants, and other crowded places with reduced ventilation.

As Prather, et al. (2020) observe, "Aerosol transmission of viruses must be acknowledged as a key factor leading to the spread of infectious respiratory diseases. Evidence suggests that SARS-CoV-2 is silently spreading in aerosols exhaled by highly contagious infected individuals with no symptoms. Owing to their smaller size, aerosols may lead to higher severity of COVID-19 because virus-containing aerosols penetrate more deeply into the lungs (10). It is essential that control measures be introduced to reduce aerosol transmission. A multidisciplinary approach is needed to address a wide range of factors that lead to the production and airborne transmission of respiratory viruses, including the minimum virus titer required to cause COVID-19; viral load emitted as a function of droplet size before, during, and after infection; viability of the virus indoors and outdoors; mechanisms of transmission; airborne concentrations; and spatial patterns. More studies of the filtering efficiency of different types of masks are also needed. COVID-19 has inspired research that is already leading to a better understanding of the importance of airborne transmission of respiratory disease."

Reference: Prather KA, Wang CC and Schooley RT. Reducing transmission of SARS-CoV-2. Science. May 27, 2020. DOI: 10.1126/science.abc6197

Source: American Association for the Advancement of Science