TOKYO -- While Japan's northernmost prefecture of Hokkaido has recently been experiencing a surge in novel coronavirus infections, there have been growing concerns across the country that the risk of infection will increase during the winter as people spend more time indoors with poor ventilation.
Seasonal influenza activity is said to usually peak in the winter, and it has been pointed out that novel coronavirus infections may also surge again during the approaching season when temperatures and humidity are low. It is important to ventilate rooms frequently in order to avoid the creation of confined spaces, which is among the "three Cs" that includes crowded places and close contact that increase transmission risks. The Ministry of Health, Labor and Welfare advises people to take the ventilation measure of "opening the windows on two sides of a room twice an hour or more," and to use 24-hour ventilation systems appropriately.
However, ventilation tends to become insufficient in the winter as people try to trap heat in rooms. Masaya Saito, professor of architectural and environmental studies at Sapporo City University, commented, "There is a drastic difference between indoor and outdoor temperatures during the winter, and it is difficult to maintain a comfortable room temperature." There is also the risk of becoming sick if windows are opened to ventilate rooms, causing a sudden change in temperature.
Professor Saito recommends a two-stage ventilation method that gradually incorporates external air into the room. For example, in the case of homes, windows of adjacent rooms that are not being used can be opened, instead of rooms occupied by residents, in order to have air come in from outside bit by bit. It is also important to let air that has amassed in the occupied room leave the room by opening doors and windows.
Viruses are said to be more active in low humidity. Yoshihide Yamamoto, associate professor of architecture and environmental engineering at Tokyo Polytechnic University, pointed out that it is necessary to maintain a humidity of at least 40% in rooms by using humidifiers among other means. He said, "It is important to take ventilation measures and manage humidity in a balanced manner, while taking thorough basic countermeasures, such as washing your hands and gargling."
(Japanese original by Ayumu Iwasaki, Science & Environment News Department)