The study has shown that if the relative humidity of a household is above or less than 40-60%, it simultaneously increases risk of contracting Covid-19 and subsequent death.
More people are comfortable with a relative humidity between between 30 and 50%. The relative humidity within an airplane remains 20%. The study that was published in the Journal of the Royal Society Interface found a strong connection between regional outbreaks and indoor relative humidity.
The study showed that whenever a region experienced a rise in Covid-19 cases and deaths of people who were not vaccinated, the estimated indoor relative humidity in that region, on average, was either lower than 40 per cent or higher than 60 per cent regardless of season.
The researchers noted, that most societies spend more than 90 per cent of their time indoors, where the majority of viral transmission has been shown to occur. Further, indoor conditions can be quite different from outdoor conditions as a result of climate control systems, such as heaters that significantly dry out indoor air.
For more answers, the team focused on the early period of the pandemic when vaccines were not yet available, reasoning that vaccinated populations would obscure the influence of any other factor such as indoor humidity.
For each country, they also tracked the local Covid-19 related policies, such as isolation, quarantine, and testing measures, and their statistical association with Covid-19 outcomes.
For each day that Covid-19 data was available, they used meteorological data to calculate a country's outdoor relative humidity. They then estimated the average indoor relative humidity, based on outdoor relative humidity and guidelines on temperature ranges for human comfort, the study said.
For instance, guidelines report that humans are comfortable between 66 to 77 degrees Fahrenheit indoors. They also assumed that on average, most populations have the means to heat indoor spaces to comfortable temperatures and accordingly they calculated the associated drop in indoor relative humidity, the study said.
Finally, they also collected experimental data, which they used to validate their estimation approach, the study said.
While outdoor humidity remained around 50 per cent throughout the year, indoor relative humidity for countries in the Northern and Southern Hemispheres dropped below 40 percent in their respective colder periods, when Covid-19 cases and deaths also spiked in these regions, the study observed.
For countries in the tropics, relative humidity was about the same indoors and outdoors throughout the year, with a gradual rise indoors during the region's summer season, when high outdoor humidity likely raised the indoor relative humidity over 60 percent. They found this rise mirrored the gradual increase in Covid-19 deaths in the tropics, the study said.
