Masks and a good ventilation system are more important than social distancing for reducing the airborne spread of COVID-19 inside a room, a modelling study suggests.

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In the research, published in the journal Physics of Fluids, the researchers created a computer model of a classroom with students and a teacher. They then modelled airflow and disease transmission and calculated airborne-driven transmission risk. The classroom model was 709 square feet with 9-foot-tall ceilings, similar to a smaller-size classroom.

The model had masked students any one of whom could be infected and a masked teacher at the front of the classroom. "The research is important as it provides guidance on how we are understanding safety in indoor environments", said Michael Kinzel, an assistant professor at the University of Central Florida in the US. "The study finds that aerosol transmission routes do not display a need for six feet social distancing when masks are mandated", Kinzel said.

The study highlights that with masks, transmission probability does not decrease with increased physical distancing, which emphasises how mask mandates may be important to increasing capacity in schools and other places, according to the researchers. The team examined the classroom using two scenarios, a ventilated classroom and an unventilated one and using two models, Wells-Riley and Computational Fluid Dynamics. Wells-Riley is commonly used to assess indoor transmission probability and Computational Fluid Dynamics is often used to understand the aerodynamics of cars, aircraft and the underwater movement of submarines. Masks were shown to be beneficial by preventing direct exposure of aerosols, as they provide a weak puff of warm air that causes aerosols to move vertically, thus preventing them from reaching adjacent students, Kinzel said.

The researchers noted that a ventilation system in combination with a good air filter reduced the infection risk by 40 to 50 per cent compared to a classroom with no ventilation. This is because the ventilation system creates a steady current of airflow that circulates many of the aerosols into a filter that removes a portion of the aerosols compared to the no-ventilation scenario where the aerosols congregate above the people in the room. These results corroborate recent guidelines from the US Centers for Disease Control and Prevention (CDC) that recommend reducing social distancing in elementary schools from six to three feet when mask use is universal, Kinzel said. "If we compare infection probabilities when wearing masks, three feet of social distancing did not indicate an increase in infection probability with respect to six feet, which may provide evidence for schools and other businesses to safely operate through the rest of the pandemic", Kinzel said.

The results suggest exactly what the CDC is doing, that ventilation systems and mask usage are most important for preventing transmission and that social distancing would be the first thing to relax, the researcher added.