The Research That Led WHO To Change Stand That COVID-19 Is Airborne

Linsey Marr, an aerosol scientist, and her team took a relook at droplet-aerosol dichotomy and came up with new facts.

The Research That Led WHO To Change Stand That COVID-19 Is Airborne

Linsey Marr and her team's research challenged the existing theories about COVID-19 spread.

In 2020, when COVID-19 was spreading across the world, a team of scientists took the challenge of correcting a historical wrong that caused the World Health Organisation (WHO) to issue advisories that proved to be harmful for people. The effort was led by Linsey Marr, an aerosol scientist at Virginia Tech. The group of 35 scientists tried to explain to the WHO officials to change their stand that COVID-19 is not airborne. In a lengthy article in The Wired last year, she explained how they approached the herculean task, the setbacks and finally how they tasted success.

Ms Marr's interest in the topic arose after a tweet from the WHO in March that year that said: "FACT: #COVID19 is NOT airborne." The aerosol scientist is one of the few in the world who also studies infectious diseases. To her, the coronavirus looked as if it could hang in the air. And this fact posed a considerable risk for people indoors.

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She tried to explain this to WHO scientists in a Zoom meeting presenting a list of superspreading events in restaurants, call centers, cruise ships and a choir rehearsal. This challenged the WHO's main safety guidelines of keeping 3 to 5 feet distance between people and frequent handwashing. Her team questioned if the virus travelled only in large droplets that immediately fell to the ground, wouldn't social distancing and handwashing have prevented such outbreaks? But the WHO experts were not impressed and the result of the meeting was not fruitful.

The heart of the problem lied in the size of the particles. For WHO, the word airborne applied to particles smaller than 5 microns. Ms Marr and the other scientists were determined to change that. Her previous research about spread of flu infection among children at day care had led to the publication of a groundbreaking study that found that flu virus in droplets that were small enough remained floating for an hour or more. The conclusion suggested that infection spread to people sharing the same air.

Luis Jimenez, atmospheric chemist at the University of Colorado Boulder, Virginia Tech scholar named Tom Ewing and graduate student Katie Randall, together with Ms Marr, then began to dig deep into the history to find out where the figure of 5 microns came from. Their efforts were emboldened by a research paper written by Yuguo Li, an indoor air researcher at University of Hong Kong. His team had concluded that most colds, flu and other respiratory illnesses must spread through aerosols and not droplets.

During the research, Ms Randall came across a book written by a Harvard engineer named William Firth Wells, which was published in 1955. That research had also delved into the droplet-aerosol dichotomy, but gave the idea that the particle size should have pivoted around 100 microns, and not 5.

They also came across the works of Alexander Langmuir, the chief epidemiologist of the newly established CDC, who first disparaged and then acknowledged Wells' work. The Harvard scientists proved that tuberculosis could be airborne. Mr Langmuir even thanked him, after his death, for illuminating their inadequate response to the disease.

Till October, the team was fighting to change the 5-micron threshold. They even approached Antony Fauci, a leading health expert in the US, sending him slides to show how the trajectory of a 5-micron particle released from a person's mouth went farther than six feet. He later endorsed the findings, saying during an address at Harvard Medical School that the 5-micron distinction was wrong.

All these efforts finally led to WHO updating its advisories, recommending that everyone always wear a mask indoors wherever Covid-19 is spreading. The CDC too acknowledged the facts presented by MS Marr and the team. By April 2021, a year after the Zoom meeting, the WHO quietly updated a page on its website, acknowledging that the virus can spread via aerosols as well as larger droplets.

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