COVID-19 Combat.

“As people go indoors in hot weather and the rebreathed air fraction goes up, the risk of infection is quite dramatic.”
— Edward Nardell, Harvard Medical School

Edward Nardell, professor of medicine and of global health and social medicine at Harvard Medical School (HMS) and professor of environmental health and of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health, said that hot summer temperatures can create situations similar to those in winter.

When respiratory ailments tend to surge, driving people indoors to breathe — and rebreathe —air that typically is little refreshed from outside.

Q&A: Ventilation and air conditioning and COVID-19

Ventilation is the intentional introduction of fresh air into a space while the stale air is removed. It is done to maintain the quality of air in that space.

WHO has contributed to guidance on ventilation and air-conditioning systems in the context of COVID-19, available here.

WHO works closely with the World Meteorological Organization Joint Office for Climate and Health and the United States National Oceanic and Atmospheric Administration (NOAA) through the Global Heat Health Information Network to develop and update this guidance.

More Q&As on COVID-19 and ventilation in public spaces and buildings are available here.

Heating, ventilation and air-conditioning (HVAC) systems are used to maintain indoor air temperature and humidity at healthy and comfortable levels. A well-maintained and operated system can reduce the spread of COVID-19 in indoor spaces by increasing the rate of  air change, reducing recirculation of air and increasing the use of outdoor air. Recirculation modes (which recirculate the air) should not be used. HVAC systems should be regularly inspected, maintained, and cleaned.

At home, table or pedestal fans are safe for air circulation among family members living together who are not infected with the virus that causes COVID-19. However, fans should be avoided when people who are not part of the immediate family are visiting, since some people could have the virus despite not having symptoms. Air blowing from an infected person directly at another in closed spaces may increase the transmission of the virus from one person to another.

At home, offices or school, if the use of table or pedestal fan is unavoidable, it is important to increase outdoor air changes by opening windows and minimize the air blowing from one person (or group of people) to another person (or group of people).

The use of ceiling fans can improve circulation of outside air and avoid pockets of stagnant air in occupied space. However, it is critical to maintain good outdoor ventilation when using ceiling fans.  An efficient way to increase outdoor air exchange is by opening windows.

Some airplanes have cabin air filtration systems equipped with HEPA filters which can remove viruses and germs quickly, minimizing the duration of the exposure to any potential infectious materials produced by a cough or sneeze. The cabin air system is designed to operate most efficiently by delivering approximately 50 percent outside air and 50 percent filtered, recirculated air. The air supply is essentially sterile and particle-free.  However, adequate ventilation is just one of the preventive measures to reduce the risk of COVID-19 transmission.  Other important measures include maintaining physical distance of at least 1 meter whenever possible, frequent hand hygiene and wearing a mask. Passengers should check with the airline company and the national or local guidelines about when and where to wear a mask while flying.