Covid-19 is airborne, scientists say. Now, the authorities think so, too

Aerosol particles, which can linger for hours and travel indoors, have stoked controversy.
Aerosol particles, which can linger for hours and travel indoors, have stoked controversy.PHOTO: AFP

WASHINGTON (BLOOMBERG) - A quiet revolution has permeated global health circles. The authorities have come to accept what many researchers have argued for over a year: The coronavirus can spread through the air.

That new acceptance, by the World Health Organisation (WHO) and the US Centres for Disease Control and Prevention, comes with concrete implications: Scientists are calling for ventilation systems to be overhauled like public water supplies were in the 1800s after fetid pipes were found to harbour cholera.

Cleaner indoor air will not just fight the pandemic, it will minimise the risk of catching flu and other respiratory infections that cost the US more than US$50 billion (S$66.63 billion) a year, researchers said in a study in the journal Science on Friday (May 14).

Avoiding these germs and their associated sickness and productivity losses would, therefore, offset the cost of upgrading ventilation and filtration in buildings.

"We are used to the fact that we have clean water coming from our taps," said Dr Lidia Morawska, a distinguished professor at the School of Earth and Atmospheric Sciences at the Queensland University of Technology in Brisbane, Australia, who led the study. Likewise, "we should expect clean, pollutant- and pathogen-free air" from indoor spaces, she said over Zoom.

The study's authors, comprising 39 scientists from 14 countries, are demanding universal recognition that infections can be prevented by improving indoor ventilation systems.

They want the WHO to extend its indoor air quality guidelines to cover airborne pathogens, and for building ventilation standards to include higher airflow, filtration and disinfection rates, and monitors that enable the public to gauge the quality of the air they are breathing.

A "paradigm shift is needed on the scale that occurred when Chadwick's Sanitary Report in 1842 led the British government to encourage cities to organise clean water supplies and centralised sewage systems", they wrote.

"No one takes responsibility for the air," Dr Morawska said. "It's kind of accepted that the air could be of whatever quality - containing viruses and pathogens."

Sars-CoV-2 multiplies in the respiratory tract, enabling it to spread in particles of varying sizes emitted from an infected person's nose and throat during breathing, speaking, singing, coughing and sneezing.

The biggest particles, including visible spatters of spittle, fall fast, settling on the ground or nearby surfaces, whereas the tiniest - aerosols invisible to the naked eye - can be carried farther and stay aloft longer, depending on humidity, temperature and airflow.

It is these aerosol particles, which can linger for hours and travel indoors, that have stoked controversy.

Although airborne infections, like tuberculosis, measles and chickenpox are harder to trace than pathogens transmitted in tainted food and water, research over the past 16 months supports the role aerosols play in spreading the pandemic virus.

That has led to official recommendations for public mask-wearing and other infection-control strategies. But, even those came after aerosol scientists lobbied for more-stringent measures to minimise risk.

Dr Morawska and a colleague published an open letter backed by 239 scientists last July requesting that the authorities endorse additional precautions, such as increasing ventilation and avoiding recirculating potentially virus-laden air in buildings.

WHO guidance has been amended at least twice since, though the Geneva-based organisation maintains that the coronavirus spreads "mainly between people who are in close contact with each other, typically within 1m".

Dr Morawska, who heads a WHO collaborating centre on air quality and health, says that is an oversimplification.

"There's nothing magic about this 1m," Dr Morawska said. The closer to an infected person, the higher the concentration of infectious particles and the shorter the exposure time needed for infection to occur. "As you are moving away, the concentration decreases," she said.

Infectious aerosols remain concentrated in the air longer in poorly ventilated, confined indoor spaces, according to Dr Morawska.

Although a high density of people in such settings increases the number of people potentially exposed to an airborne infection, enclosed indoor areas that are not crowded may also be hazardous - a distinction Dr Morawska says the WHO should make clearer.

"The WHO, step by step, is modifying the language," she said.

Dr Morawska, a Polish-born physicist who was previously a fellow of the International Atomic Energy Agency, can take credit for the WHO's changing stance, said Dr Raina MacIntyre, professor of global biosecurity at the University of New South Wales in Sydney.

"Professor Morawska's contribution, on the background of world-leading expertise in aerosol science, made a real impact by forcing WHO's hand," Dr MacIntyre said in an email.

The role of airborne transmission "has been denied for so long, partly because expert groups that advise government have not included engineers, aerosol scientists, occupational hygienists and multidisciplinary environmental health experts," Dr MacIntyre wrote in The Conversation last week.

"A false narrative dominated public discussion for over a year," she said. "This resulted in hygiene theatre - scrubbing of hands and surfaces for little gain - while the pandemic wreaked mass destruction on the world."

Some people working in infection prevention and control and related fields have stuck rigidly to beliefs that minimised aerosol transmission, despite evidence challenging their views because "they do not want to lose face", said Dr Julian Tang, a clinical virologist and honorary associate professor in the department of respiratory sciences at England's University of Leicester.

"We all have to adapt and progress as new data become available," Dr Tang said. That is especially true in public health, where official policies and guidance based on "outdated and unsupported thinking and attitudes can cost lives", he said.

Dr Morawska said she hopes the attention that the pandemic has drawn to face masks and the risks associated with inhaling someone else's exhaled breath will be a catalyst for cleaner indoor air.

"If we don't do the things we are saying now, next time a pandemic comes, especially one caused by a respiratory pathogen, it will be the same," she said.