A group of leading scientists and physicians specialising in immunobiology and infection control have launched a petition calling on the World Health Organisation (WHO) to provide clear guidelines on the recommended humidity levels in public buildings.

The petition calls for swift and decisive action to establish global guidance on indoor air quality, with a clear recommendation on the minimum lower limit of air humidity in public buildings.

“This critical move would reduce the spread of airborne bacteria and viruses in buildings and protect public health,” the petition says.

Supported by leading members of the global scientific and medical community, the petition is designed to not only increase global awareness among the public on the crucial role indoor environmental quality plays in physical health, but also to call emphatically on the WHO to drive meaningful policy change; a critical necessity during and after the Covid-19 crisis. 

As COVID-19 continues to put pressure on health systems and the economy globally, the group calls on the WHO to review the extensive research that shows an indoor humidity level of between the40% - 60%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, Professor of immunobiology at Yale, said 90% of people’s lives are spent indoors.

“When cold outdoor air with little moisture is heated indoors, the air’s relative humidity drops to about 20%. This dry air provides a clear pathway for airborne viruses, such as COVID-19,” he said.

“That is 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% RH.

Evidence shows the important role indoor humidity levels play in preventing virus transmission.”

One of the leading forces in the charge for a globally recognised 40-60%RH guideline for public buildings is Dr Stephanie Taylor, MD, Infection Control Consultant at Harvard Medical School, ASHRAE Distinguished Lecturer & Member of the ASHRAE Epidemic Task Group.

In light of the COVID-19 crisis, Dr Taylor said it is now more important than ever to listen to the evidence that shows optimum humidity can improve indoor air quality and respiratory health.

“It is time for regulators to place management of the built environment at the very centre of disease control,” she said.

“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.”

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