On March 28, 2020, in the opening stages of the pandemic, the World Health Organization (WHO) tweeted: “FACT: #COVID19 is NOT airborne.” 

It turned out they were very wrong. 

The world’s response to the COVID-19 pandemic has seen a number of screw-ups: some countries waited too long to lock down, some flip-flopped on their stance on face masks. Perhaps a few hiccups should be expected when you consider there was no rehearsal for this “unprecedented” event (unless you consider SARS and MERS). 

However, of all mistakes, one of the biggest has seemingly slipped under the radar: the question of airborne transmission. 

Scientists who study airborne transmission agree that SARS-CoV-2 is spread by aerosols, teeny microscopic respiratory particles that can float in the air – almost certainly the most important route of transmission.

Despite this, many of the world’s health authorities and governments have repeatedly dragged their feet in accepting and broadcasting this due to dogma, fear, and desperately outdated science.

In early 2020, scientists were working to understand the novel virus that had sprung out of Wuhan, China, and was popping up across the world. Among the stream of scientific papers and news reports on the outbreak, one feature was especially striking: super-spreader events. 

In mid-February 2020, over 5,000 members of the Shincheonji Church of Jesus religious sect in South Korea caught COVID-19. Practically all of the cases seem to have originally stemmed from one woman, "Patient 31.” 

Similar superspreader events started to be reported elsewhere in the world, from cruise ships to bars. These stories caught the attention of Professor Linsey Marr, an environmental engineer and aerosol scientist studying viruses in the air at Virginia Tech. By her counts, Marr is one of the five or so scientists in the world studying this overlap between how particles move around in the air and the airborne transmission of viruses.

Watching the news of COVID-19 come out of China, Marr and a handful of other scientists started to strongly suspect that this virus was not primarily spread by visible droplets of spit and snot coughed or sneezed out of an infected person, but through microscopic airborne aerosols. 

However, at first, the WHO and other health authorities weren’t convinced that aerosols were a problem. “COVID-19 is NOT airborne,” they boldly claimed. Many governments followed suit, stressing the importance of washing hands and hand sanitizers. The word “airborne” was not mentioned in any of their posters, websites, or even scientific guidance. 

“It was like this loaded word for them. They were really kicking themselves in the shins because that word is the best way to explain how this is spreading to the general public,” Professor Marr told IFLScience.

“In reality, a lot of transmission happens from breathing in these small particles from the air, breathing in the virus, both at close distances and far distances. This is more likely when you’re close to someone. It’s like standing next to someone smoking: you’ll be exposed to more of the smoke if you're close to them,” explained Marr.

The difference may seem subtle, but it has some hefty implications. Mucus droplets containing the virus can be briefly airborne but will quickly fall to the ground. They can only transmit the virus if they’re directly blown in another person’s direction or if they land on a surface, such as a handrail or a doorknob, and an unsuspecting person puts their fingers in their mouth. 

Airborne aerosols, however, are a different beast altogether. These significantly smaller particles can stay airborne for significantly longer. In a stuffy, poorly ventilated room, virus-loaded aerosols can hang in the air for a significantly longer time. Infected people are also more likely to exhale them simply through breathing and talking, as opposed to coughs and sneezes.

In theory, if an infected person breathes in a train carriage, classroom, bar, or shop, infectious aerosols could still be hovering in the space perhaps hours after they left. Acknowledging airborne transmission also changes how we prevent the spread of the virus – if aerosols are involved then pricey precautions like specialized isolation wards and N95 masks are all the more important. 

Marr, plus a host of other aerosol scientists, knew they had a task ahead of them in the first stage of the pandemic. Despite their efforts, little progress had been made months later. By July 2020, 238 scientists wrote an open letter to the WHO demanding they recognize and mitigate airborne transmission of COVID-19. A stream of studies came out affirming the stance that COVID-19 was airborne, but it took almost a year to catch the attention of public health authorities. 

“At this point, they didn’t want to acknowledge the disease is airborne because they didn’t initially,” Marr explained. 

In May 2021, the WHO and the US CDC finally updated their scientific advice on COVID-19 transmission, acknowledging that the virus spreads via airborne particles. However, their public-facing guides still shied away from clearly and explicitly stating this. Marr has a few suspicions as to why.

“It’s a misunderstanding that came from the mid-1900s when different routes of transmission were first defined and some influential voices who really emphasized these large visible droplets when people are close to each other that fly through the air like spitballs,” Marr explained

The old belief was that particles over a certain size counted as droplets and were not airborne. However, there is no reason to rigidly stick to this; depending on all manner of different environmental conditions, like temperature and airspeed, particles above this set size can still remain airborne and infectious. Many authorities, however, stuck to the old dogma.

“There’s people in the WHO who are really dedicated to the traditional definition and the dogma. They really want to promote handwashing and things that they understand,” Marr continued. “How things move around in the air is really outside of their expertise. The World Health Organization really doesn’t have anyone on its committees that understands this.”

On top of scientific misunderstanding, there may be other active intentions at play. Firstly, she suspects that the WHO felt the word “airborne” might scare the public, as if COVID-19 was spread like a monstrous cloud leaping from home to home. Secondly, acknowledging airborne transmission could be costly.  

“Part of it is the lack of the correct scientific understanding, but also there were also forces that wanted this to be true because of the hospital infection control is set up,” Marr said. 

“If they say the word airborne, that means they need lots of resources to handle the disease. They need n95 face masks or some kind of medical respiratory for everyone, all of the workers at the hospital. They’d need negative pressure isolation rooms for all the patients. These are very resource intensive, so there’s reluctance to do this,” she resigned.

Airborne transmission and aerosols have slowly but surely crept their way into the COVID-19 lexicon, although still only receive cursory mentions in some infection control guidelines on the WHO’s website.

Science is ever-evolving, and our understanding of COVID-19 has grown dramatically in the past two years. With this, miscalculations have no doubt been made with public health measures and messaging, although it’s impossible to quantify the cost of these blunders. 

Looking forward, we can learn from this. Marr believes that COVID-19 has redefined airborne transmission, and this pandemic could spark new ways of thinking about disease, everyday life, and the spaces we inhabit. However, welcoming this new paradigm will require us to chuck out many assumptions and stigma.

“In terms of a paradigm shift, we live with these airborne diseases, such as colds and flu. People used to live with more water-borne diseases, just accepting them as a way of life, until they realized you can start treating the water. Moving forward, I hope we start thinking about how we design indoor spaces and handle the air within,” Marr finishes.