Scientists have determined the level of humidity at which the transmission of coronavirus slows down

According to a new study, relative humidity of 40 to 60 percent in a room can hinder the transmission of SARS-CoV-2. However, scientists warn that the virus can still be transmitted by contact and is stored on the surfaces of objects.

The COVID-19 pandemic is still in full swing, and both authorities and scientists are trying to find ways to slow the spread of the infection. Last week, China – the “homeland” of the outbreak – announced that it was able to defeat the epidemic. Most will agree that this was done mainly due to quarantine, the coordinated work of Chinese doctors, as well as the organization and responsibility of local residents.

However, researchers continue to explore other options: perhaps the spread of the virus has slowed down due to the arrival of spring and an increase in air temperature? Indeed, statistics recall that now infections are most susceptible to countries where it is relatively cold. There are already several researches on this subject suggesting a relationship between temperature, wind speed, relative humidity, and COVID-19. However, experts warn that we still know too little about SARS-CoV-2 to talk with confidence about its seasonality.

However, this does not prevent the search for ways to hinder the transmission of infection indoors. This, in particular, is the work of scientists from the Yale School of Medicine and the University of Zurich, previously published in the Annual Review of Virology and on the website of Yale University. So, the researchers argue that our chances of overcoming the pandemic are affected not only by timely quarantine measures and social distance but also by the microclimate in buildings, apartments and other rooms – or rather, relative humidity.



“We spend ninety percent of our lives indoors, in close proximity to each other”, says Akiko Iwasaki, immunobiologist and senior research author. “What we have not talked about before is the relationship between temperature and humidity in the room and on the street and the transmission of the virus by air”.

Scientists explain that the winter climate makes viruses three times more dangerous: when the cold outside air, containing a small amount of moisture, heats up in the room, the relative humidity there drops to about 20 percent, and the virus particles get a free path for spread. In addition, the ability of the human immune system to respond to pathogens is suppressed in drier air.

To confirm their arguments, the authors conducted a study on rodents. Infected mice more easily transmitted viral particles through the air to their uninfected neighbors – provided that the relative humidity in the cells where they were kept was low. In an environment with a relative humidity of 40 to 60 percent, the subjects demonstrated a lower (and significantly) ability to transmit viruses to others. Moreover, in a room with high relative humidity, the respiratory virus received favorable conditions for spread and more often settled on surfaces.

In this regard, the authors of the work remind: the results do not mean at all that residents of hot countries can relax and forget about the importance of surface disinfection and personal hygiene, as well as that coronavirus, is transmitted through close contact with the infected. However, maintaining a relative humidity of 50 percent in homes is still recommended.

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