Airborne transmission of SARS-CoV-2: ventilation improvement strategies in preparation for school re-opening

Short-range airborne transmission is currently recognised as a predominant route for transmission of SARS-CoV-2.1 The US Centers for Disease Control and Prevention have also acknowledged the importance of transmission of coronavirus disease 2019 (COVID-19) through inhalation of viruses in the air at distances farther than six feet (2 m).2Several important factors contribute to increased risk, including: enclosed space with inadequate ventilation; increased exhalation of respiratory fluid (eg, shouting, singing, exercise); and prolonged exposure ([greater than]15 minutes). In the US, fresh air supply in classrooms (for ages 5-8 and [greater than or equal to]9 years) and other education facilities should be at least 5 L/s per person, in accordance with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standard 62.1-2016.9 In Hong Kong, standards for new buildings recommend that fresh air provision in normally occupied spaces should exceed the minimum ASHRAE standard by at least 30%.10 Applied to the school setting, this would be equivalent to 6.5 L/s per person. Schools, just like restaurants, are subject to the same risk, because compliance with mask wearing advice, especially among children, cannot be guaranteed at all times. [...]all possible measures should be optimised before the resumption of schools in September 2021.