We know proper indoor ventilation is key to reducing the spread of Covid-19. Now, a study by MIT researchers finds that indoor relative humidity may also influence transmission of the virus. Relative humidity is the amount of moisture in the air compared to the total moisture the air can hold at a given temperature before saturating and forming condensation. In a study appearing today in the Journal of the Royal Society Interface, the MIT team reports that maintaining an indoor relative humidity between 40 and 60 percent is associated with…