A global petition led by a group of scientists specialising in immunobiology and infection control calls on the World Health Organization (WHO) to establish global guidance on indoor air quality.
The scientists wish to establish a clear recommendation on the minimum lower limit of air humidity in public buildings. Their petition specifically and directly targets the WHO because of its pivotal role in setting global guidelines for indoor air quality.
The scientists believe that if such steps were implemented it could reduce seasonal respiratory illnesses and lessen the burden on healthcare systems and other knock-on benefits. This “critical move would reduce the spread of airborne bacteria and viruses in buildings and protect public health”.
The petition is designed to increase global awareness among the public on the crucial role indoor environmental quality plays in physical health as well as calling on the WHO to change policy, which they contend is a critical necessity during and after the Covid-19 crisis.
As battling the virus continues to put pressure on health systems and the global economy, the group wants the WHO to review the extensive research that shows an indoor humidity level of between the 40 per cent – 60 per cent relative humidity (RH) – is the optimum threshold for inhibiting the spread of respiratory viruses such as influenza. This is a threshold that many public buildings drop below every winter.
Dr Akiko Iwasaki PhD, who is the Waldemar Von Zedtwitz professor of immunobiology and professor of molecular, cellular and developmental biology at Yale, and an investigator for the Howard Hughes Medical Institute, said: “Ninety per cent of our lives in the developed world are spent indoors in close proximity to each other. When cold outdoor air with little moisture is heated indoors, the air’s relative humidity drops to about 20 per cent. This dry air provides a clear pathway for airborne viruses, such as Covid-19. That’s why I recommend humidifiers during the winter, and why I feel the world would be a healthier place if all our public buildings kept their indoor air at 40 to 60 per cent RH.”
Evidence shows the important role indoor humidity levels play in preventing virus transmission and improving immune system response. There are three key findings suggesting why indoor air should be maintained at 40-60 per cent RH in public buildings such as hospitals, care homes, schools and offices.
•Breathing dry air impairs our respiratory immune system’s ability to efficiently capture, remove and fight airborne viruses and germs, rendering us more vulnerable to respiratory infections.
•When the RH is lower than 40 per cent, airborne droplets containing viruses, such as SARS-CoV-2, shrink through evaporation, making them lighter. This enables the particles to float for longer in the air, increasing the likelihood of infection.
•Most respiratory viruses suspended in dry atmospheres survive and remain infectious for far longer than those floating in the air with an optimum humidity of 40-60 per cent RH.
Dr Stephanie Taylor, infection control consultant at Harvard Medical School, said: “It is time for regulators to place management of the built environment at the very centre of disease control. Introducing WHO guidelines on minimum lower limits of relative humidity for public buildings has the potential to set a new standard for indoor air and improve the lives and health of millions of people.”
Dr Walter Hugentobler, a former lecturer in primary care at the University of Zürich, added: “Raising air humidity by humidification reduces the risk of virus spread in hospitals and other buildings at low-cost and without causing negative effects. It can also be easily implemented in public buildings, both in private and workplace environments with relative ease. Humidification gives people a simple means of actively combating seasonal respiratory infections.”