The airborne transmission of the coronavirus SARS-CoV-2 via aerosol particles in indoor environment seems to be strongly influenced by relative humidity, concludes the analysis of 10 most relevant international studies on the subject. Therefore, they recommend controlling the indoor air in addition to the usual measures such as social distancing and masks. A relative humidity of 40 to 60 percent could reduce the spread of the viruses and their absorption through the nasal mucous membrane.