There are a number of studies that provide conflicting answers to this question. Some research suggests that high humidity slows the spread of the new coronavirus, while other research states that high humidity is more conducive to the spread of the virus. There are even a few studies suggesting that high humidity levels can cause a severe spread of the pandemic. There are a number of case studies to support the position that humidity does play a key role in the spread of seasonal diseases. One of these reports, led by Jin Bu of the Chinese Academy of Medical Sciences, found that the virus seemed to spread more easily in 75% relative humidity with precipitation less than 30 mm per month. This research, however, conflicts with all other studies on the subject.
Dr. Alan Evangelista, Professor of Microbiology and Virology at St. Christopher’s Hospital for Children in Philadelphia, USA, has been studying coronaviruses and influenza particles for many years. Dr. Alan’s research indicates that as humidity increases, the viral droplet size becomes larger and rises from the body into the air more quickly. In contrast, when humidity is low, there is more rapid evaporation of respiratory droplets and they remain airborne for longer periods, thus increasing the chance of transmission.
The fact remains, however, that every year during the rainy season, Thailand encounters an influenza outbreak. The Department of Disease Control concluded in its summary of the 2019 influenza outbreak that there were a total of 390,733 patients and 27 deaths. The groups experiencing the highest illness rates were small and school-aged children. The key contributing factors to the outbreak were found to be increased humidity and cooler temperatures, which allowed the virus to survive for longer periods of time.
Prof. Yong Poovorawan, MD., Head of the Center of Excellence in Clinical Virology at the Faculty of Medicine, Chulalongkorn University, issued a warning to the public about the COVID-19 pandemic after the Thai Meteorological Department announced that as of May 18, Thailand had entered the 2020 rainy season. He stated that although at this time only a small number of infected persons have been found in Thailand, most of whom were in state quarantine having recently returned from foreign countries, the more than 100,000 new COVID-19 cases per day worldwide clearly show that this disease is difficult to control and more time is needed to develop a vaccine that can put a stop to its spread.
Protection from both of these viruses is possible using similar methods. If everyone takes stringent measures and works hard to prevent influenza, then the number of people infected with COVID-19 will also be reduced. On the other hand, because during the rainy season the risk of infection by various flu viruses is higher, the risk of COVID-19 transmission is higher as well. Steps that we must continue to strictly adhere to include frequent hand-washing, wearing a mask, eating hot foods, using personal utensils, keeping a distance of at least 1-2 meters from other people, and avoiding crowded areas that are not well-ventilated. Extra cloth face masks should be kept on hand. If a mask gets wet in the rain it should be changed immediately, as wet masks cannot fully protect an individual from germs and bacteria.
When a person coughs or sneezes, small respiratory droplets are ejected into the air. If that person is sick, then viral particles will be contained in those droplets. We can conclude that regardless of whether the climate is humid or dry, we all need to adapt to this new way of life and strictly follow the principles of self-protection from both the influenza virus and the COVID-19 virus, as these diseases are easily transmitted from person to person.
M.D., Faculty of Medicine, Mahidol University, 1997. Faculty of Medicine Ramathibodi Hospital, Mahidol University , 2001