‘Airborne,’ ‘Asymptomatic,’ and Other Misunderstood Coronavirus Terms

‘Airborne,’ ‘Asymptomatic,’ and Other Misunderstood Coronavirus Terms
Photo: TED ALJIBE/AFP via Getty Images, Getty Images

Today, the World Health Organisation formally announced a change in its stance over very two important issues concerning covid-19. The organisation stated that people can spread the virus while asymptomatic and that airborne transmission of the virus is possible under certain circumstances, such as crowded rooms with little ventilation.

“Now, wait a minute,” you might be thinking. Didn’t we already know that people without symptoms can spread the virus? And didn’t we already know you can get the virus through the air — hence all the masks? The problem here is that scientists and health officials use terms with very specific meanings — “airborne” as defined by the WHO is not what most people think of when they hear the word.

Confusion over terms has serious consequences, since people may assume there’s an open debate about the need for masks (there isn’t) or that scientists aren’t sure whether people who don’t feel sick can spread the virus (they definitely can). So let’s clear up a few terms.

“Asymptomatic” vs “Presymptomatic” vs “Subclinical”

In June, the World Health Organisation got into hot water with much of the scientific community when one of its experts appeared to suggest that asymptomatic transmission of the virus was very rare. The expert soon walked back her comments as a misunderstanding, emphasising that some research does show the importance of asymptomatic transmission and that it’s a more complex issue than she initially suggested.

Why is it complex? Well, because being asymptomatic could actually mean several things, depending on how — and when — you ask the question.

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There are definitely people who contract the coronavirus, test positive for it, and never feel sick the entire time it takes for their bodies to clear the infection. These people could be considered truly asymptomatic. Other people can have enough of the virus inside them to test positive, not feel sick initially, but then show symptoms a few days later. These people are called presymptomatic. You also have people who are infected but experience symptoms so mild that they go unnoticed or are mistaken for something else, like allergies or jet lag; these would be called subclinical cases.

Right now, a lot of work is being done to figure out how often each of these outcomes happen and how capable each group is of transmitting the virus to others. Of the three, it’s likely that presymptomatic people can readily spread covid-19 in the few days before symptoms start. That’s why everyone, not just people who feel sick, should wear a face mask around others.

Unfortunately, when the WHO expert said that “asymptomatic” transmission was rare, many people took that as evidence that only sick-feeling people need masks, which is not the case.


On Monday, I wrote about the complex and increasingly prominent scientific debate over whether the coronavirus is airborne. The key to understanding this debate is that, whether it’s truly “airborne” or not, the coronavirus spreads through the respiratory system, meaning you can very much catch it by breathing it in.

This week, a group of over 200 scientists petitioned the World Health Organisation to recognise the potential for airborne transmission of covid-19, and they quickly got results. On Tuesday, the New York Times reported that the WHO was planning to address the letter’s concerns and would likely issue new, updated recommendations to the public regarding airborne transmission soon.

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A few readers (or headline-readers, at least) criticised my article for seeming to argue that covid-19 isn’t spread through the air or that masks are useless — which is not at all what the article suggested. Elsewhere, I had friends panicked that the virus, if airborne, is impossible to avoid and we’re all doomed. So let’s clear the air a bit.

Scientifically, a disease being airborne means it can spread very easily through microscopic aerosols that spread far and linger in the air for hours. Measles, for example, is an airborne disease, which is why it’s so contagious. A non-airborne respiratory disease, by contrast, would be spread through larger droplets, like those from sneezing and coughing, which don’t travel very far and fall to the ground fairly quickly. The flu is typically considered a non-airborne virus. However, some scientists are arguing that this binary distinction isn’t appropriate — that primarily droplet-spread viruses can be temporarily airborne under the right conditions, like in a poorly ventilated room where people are talking or singing.

The big question now is whether this short-lived airborne transmission is playing a significant role in spreading the covid-19 pandemic. But whether the virus largely spreads through droplets or aerosols, it’s still travelling through the air from our mouths and noses, meaning that face masks help to reduce the spread, as they help to block both aerosols and droplets.

This is a new disease and the science is constantly evolving, but we know it’s smart to wear a mask in public, avoid crowded indoor spaces, and avoid close contact with people outside your household as much as you can. Knowing that the virus can be airborne may prompt certain extra precautions for health care workers or for indoor spaces, such as using ultraviolet light to kill virus lingering in the air or installing better ventilation to disperse aerosols.

“Mild” illness

Many people who catch the coronavirus will recover from it with no trouble at all. On the other end of the spectrum, there are people who have life-threatening infections or secondary complications that can be fatal. But in the middle, there are the “mild” cases — people who aren’t sick enough to be hospitalized but who may be sicker than they’ve ever been in their life.

The thing is, mild is a subjective term. Sure, there are some cut-offs that doctors use when classifying a case as mild, moderate, or severe. People with mild covid-19 would typically be free of pneumonia, for example. But beyond that, a infection that’s clinically considered mild can still badly impact a person’s life long after it’s come and gone.

Take, for instance, the loss of smell and taste, which is now known to be a common symptom of covid-19. For some people, that loss may end up being permanent or their senses could be forever weakened. As one neurologist told Gizmodo in March, it’s an experience that could take away decades of smelling your favourite meal if you’re young.

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Scientists are also discovering that even seemingly mild cases can have serious ramifications for long-term health. Some people with mild respiratory symptoms of covid-19 are known to develop neurological problems like stroke, muscle weakness, and fits of delusion, which are likely caused by a flawed immune response to infection. In other mild cases, doctors have found evidence of lung damage that could affect people’s respiratory health down the road. Even the risk of newly onset diabetes might be possible with a mild infection.

Others with so-called mild illness may be extremely sick with fevers, coughing, and nausea for many weeks — a miserable and scary experience that most of us wouldn’t usually refer to as mild.

Basically, the coronavirus is like a giant cannonball in the pool of diseases we get regularly: Most of us will be fine with the extra splash, but some people — people we love and need — won’t be. It’ll take years to untangle how often these long-term complications happen, but the more widespread this pandemic becomes, the more splash damage there will ultimately be.