Back in October, 2020, we shared a link to a document of FAQs on Protecting Yourself from COVID-19 Aerosol Transmission, developed collaboratively by scientists and engineers with many years of collective research experience related to indoor air quality, aerosol science, aerosol disease transmission, and engineered control systems for aerosols. While the authors continue to update the document as research evolves, new research has also been published to further detail the role of aerosol transmission in the COVID-19 pandemic.
On May 2, 2021, a pre-print publication was released on “Indicators for Risk of Airborne Transmission in Shared Indoor Environments and their application to COVID-19 Outbreaks”. The authors propose two simple parameters as indicators of infection risk for indoor environments. They combine “the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and air cleaning rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend in relation to these parameters that is consistent with an airborne infection model, supporting the importance of airborne transmission for these outbreaks.” Their analysis shows that mitigation measures are needed to limit aerosol transmission risk in most indoor spaces. Among effective measures are reducing vocalization, avoiding intense physical activities, shortening duration, reducing occupancy, wearing high-quality well-fitting masks, increasing ventilation and applying additional virus removal measures (e.g. using HEPA filters). The authors conclude that “The use of multiple ‘layers of protection’ is needed in many situations, while a single measure (e.g. masking) may not be able to reduce risk to low levels.” The use of HEPA filters and increasing ventilation can also benefit people with asthma, as they improve indoor air quality.