In a study published in the Journal of the Royal Society Interface, researchers from MIT revealed that indoor relative humidity can also affect the virus’ ability to spread. They suggested that indoor ventilation is needed to prevent the spread of COVID-19.

The findings of the study revealed that maintaining an indoor humidity level between 40 and 60% of relative humidity was associated with relatively lower rates of COVID-19 infections and deaths, while indoor conditions outside the said range were associated with worse COVID-19 outcomes. Hence, the study recommended that the levels of indoor humidity should be between 30 and 50% relative humidity, and an airplane cabin should be around 20% relative humidity.

These findings of the study were based on COVID-19 data and meteorological measurements collected from 121 countries. Based on the data, the researchers observed that whenever a region experienced a rise in COVID-19 cases and deaths, the estimated indoor relative humidity in that region, on average, was either lower than 40% or higher than 60%, regardless of the season. 

(Source: https://theprint.in/health/maintaining-sweet-spot-indoor-humidity-levels-may-reduce-covid-19-transmission/1222680/ )