Stock child mask
A pandemic requires a collective response, from young and old alike. We wear masks for 3 reasons: to protect ourselves from people who might be infected, to protect others from our infections, and to set social standards and norms appropriate for a pandemic. Image Credit: Shutterstock


  • #COVIDisAirborne is now trending on Twitter.
  • It’s symptomatic of the debate raging between groups of scientists, notably within the WHO and those outside of it.
  • The “data war”, being waged for more than a year now, rests on the physics of viral transmission.
  • Some experts point to the primacy of aerosol-borne virus in explaining “super spreader events”, where infections spread without direct contact  involved.
  • A WHO scientist, however remains unconvinced — and has assailed the use of face masks as a trigger for “many side effects”, including acne.
  • Concerns over the "harms" of acne flies in the face of the deadly COVID tsunami

Here’s one disturbing thing about COVID: It’s an unseen enemy. Two, it’s incredibly contagious. Three, you’re already infected, yet it still doesn’t hurt. This virus from hell is so sinister you’ll never know you're a carrier, unless you get “swabbed” or start showing symptoms, a few days after contracting it.

But with swab testing inaccessible/too pricey in most parts of the world, you try and live a “normal” life — until you, and those around you, start getting feverish, sneezing like crazy and infecting others, too.

And, unfortunately, people die from COVID. The primary route of transmission? There’s a growing body of evidence it’s through aerosol — ultra-tiny particles loaded with virus wafting about in the air, especially in indoor settings. It’s how the breath-and-sneeze-of-death cycle goes on, a growing number of scientists argue.

Q: Airborne transmission downplayed?

There is, however, a very strong undercurrent within the WHO citing a “lack of scientific evidence” for that primacy-of-airborne-transmission thesis to explain the spread of COVID-19.

Until the recent past, the role of face masks had been discussed ad nauseam. A debate kicked off early in the pandemic on whether or not wearing face masks really helps protect people.

The WHO director general famously claimed “healthy people don't need to wear face masks”. At a media briefing in Geneva on April 2, 2020, WHO Director-General Tedros Adhanom Ghebreyesus warned there's “still much to learn” about the pandemic — and that guidelines and recommendations can “evolve”.

The message was clear: Wearing face masks, alone, is not an absolute guarantee of protection. Given the limited information then, Ghebreyesus stressed wearing face masks is effective only when used in conjunction with other protective measures.

Q: Face masks: From ‘don’t wear’ to ‘must have’?

How masks went from “don’t wear” to “must have” is quite another story. But it’s a clear case of disconnect between urgent public health messaging and science, which by default needs time (for validating hypothesis through experimentation/observation).

Some 3.1 million deaths and 150 million COVID infections later, much time has passed. And the world health body has been severely criticised for its prevarication over the utility face masks then. Now, it’s under fire, again.

Why? A key WHO scientific adviser has cast doubts on the predominance of airborne transmission of COVID-19 thesis following a pre-print study, commissioned by the agency, stating as much.

Q: What’s the current state of the aerosol debate?

The debate rages on, even as the global COVID crisis claims more lives and jobs. The main sticking point is physics: in particular, about the complex physical behaviour of particles that drop to the ground — versus those that float and move around like fine dust.

Droplets spewed from a sneeze, laugh, cough or talk tend to be larger than five microns in size. Due to sheer gravity, dense droplets fall to ground, about six feet away from the person sending them forth. You inhale a droplet or pick one up from surfaces, and that’s how COVID-19 spreads, like most respiratory diseases.

Image Credit: Vijith Pulikkal / Gulf News

However, compared to droplets, aerosols behave much differently. Because of their really small size, they can “float” much greater distances than two metres even attach to dust and hover in the air — for hours. They can travel on air currents, too. This has implications for rate of transmission.

There are more than 2,000 superspreader events (SSEs) that had been well documented, according to Science Direct. More than two thousands of superspreading events or outbreaks of COVID-19 have been documented.

2,000 +

number of of superspreading events or outbreaks of COVID-19 documented, according to Science Direct.

The studies concluded that “nearly all SSEs [super spreading events] in the database took place indoors.” There were identified 318 outbreaks each with a minimum of 3 cases, comprising a total of 1,245 confirmed cases in 120 prefectural cities in non-Hubei provinces, China, and found that none occurred in outdoor settings. High attack rates of COVID-19 have also been found in the following settings:

  • Choir rehearsals
  • Homeless shelters
  • Nightclubs
  • Fitness centers, and
  • Meat processing plants

It means a poorly-ventilated room could be a “super spreader” event, where a pile of people get infected by one person. There's solid evidence supporting airborne transmission of viruses.

  • One measles study that goes back to 1964 (De Jong), found that aerosolised virus was still "viable" (infectious) in the air, after significant time has passed.
  • A school outbreak study in 1978 on measles (Riley) shows high risk of aerosol-based transmission
  • A 1985 measles outbreak investigation (Block) shows "high likelihood" of transmission over "long distances" (i.e. >2 metres).
  • Between 2020 and 2021, for COVID-19, at least 15 studies show evidence bolstering airborne transmission.
  • For example, one study published in 2020 (Lednicky) shows a viable virus cultured from aerosol sample.
  • Two studies (Richard 2020, Kutter 2021) on COVID-19 in which humans are the only natural host, shows evidence of viral transmission through the air.
aerosol airborne transmission
Image Credit: Jay Hilotin / Gulf News

And that explains how "superspreader events" (SSE) happen, especially in indoor settings, according to Twitter-savvy physician-scientist Eric Topol. While airborne transmission of respiratory viruses is difficult to demonstrate directly, a Lancet article pointed to “10 streams of evidence” that collectively support the hypothesis that SARS-CoV-2 is transmitted primarily by the airborne route.

The most remarkable of which is point #6: Viable SARS-CoV-2 has been detected in the air. In laboratory experiments, SARS-CoV-2 stayed infectious in the air for up to 3 hours with a half-life of 1·1hour. "Viable SARS-CoV-2 was identified in air samples from rooms occupied by COVID-19 patients in the absence of aerosol-generating health-care procedures and in air samples from an infected person's car."

There had been documented superspreader events via elevator use, especially when people carelessly chat away while inside a lift.  

Q: Why is the WHO coming under attack again?

Basically, it’s because of its stance as an institution perceived to “downplay” aerosol transmission — and again, over the utility of face masks. Dr. John Conly, a top adviser to the WHO, has made controversial comments downplaying the risk of the coronavirus’ airborne spread.

On April 9, 2021, during a panel discussion at the University of Calgary on the role of airborne transmission in the COVID-19 pandemic, Dr Conly said that N95 masks can cause "harms" — including acne.

“Any time you look at benefits, you need to look at harms, of which there are many harms with N95s — and I think to ignore them you are at your peril,” Conly told the forum. “There is acne, also issues with eczema, conjunctivitis, CO2 retention; there has been decreased O2 concentrations in pregnant women — many side-effects to this.”

Some scientists find that the concern over acne-from-masks absurd, at least given the spike of cases and deaths, especially in India, now facing a COVID "tsunami".

Q: What did Dr Conly say about the airborne transmission?

“We absolutely know there are situational airborne settings,” Dr Conly told the April 9 panel. “But to be able to say that it is the only and predominant means, I think we need better scientific evidence.” Such statements offer important clues into the thinking of the WHO leadership.

Such statements offer important clues into the thinking of the WHO leadership. Dr Conly is seen as a WHO heavyweight, as he chairs the WHO’s Infection Prevention and Control Research and Development Expert Group for COVID-19. The group makes key decisions on the research that informs the world body’s recommendations.

Q: Why was the WHO criticised over its denial of the primacy of aerosol transmission?

It's due to its insistence on the so-called "droplet dogma". It's not the first time that the WHO faced criticisms over its reluctance to acknowledge aerosol transmission — or microscopic airborne particles — as a primary driver of the pandemic.

Other experts say Dr Conly is at the heart of the issue within the world body. “Frankly, I think he just can't admit he's wrong,” said Linsey Marr, an expert on the airborne transmission of viruses at Virginia Tech told CBC Canada. "He does carry a lot of weight with WHO, and unfortunately I think his thinking is still stuck in what we knew 20 or 30 years ago and hasn't updated with what we've learned since then — and especially what we've learned over the past year.”

WHO Director General Tedros Adhanom Ghebreyesus
Calling for solidarity and firm leadership from countries, WHO Director General Tedros Adhanom Ghebreyesus said there had been marked differences in the number of cases around the world. Image Credit: AP

Q: Who are the critics of the WHO position on airborne infections?

One is Kimberly Prather, a professor at the UC San Diego, and an airborne viruses researcher. “It is not OK that people in India are still cleaning surfaces while the rest of the world knows this virus is in the air,” Dr Prather fired away on Twitter on Tuesday (April 27, 2021). “Everyone deserves to know the truth regardless of whether they are rich or poor. Please @WHO let the world know that #COVIDisAirborne."

What is airborne transmission?
Droplets less than five micrometers in diameter are aerosols, according to the WHO definition. By comparison, droplets expelled through the air when people cough and sneeze are referred to as “respiratory droplets”. They are usually larger in size, do not linger in the air, spread when people are in close contact with each other, and can drop on to and contaminate surfaces, including hands.

Source: US CDC (published October 5, 2020)

Q: What should people do to protect themselves from aerosol transmission, now that we know the virus is airborne?

Dr Prather advises people to “wear good fitting masks, avoid crowded indoor locations where people don’t wear masks, open doors and windows, spend time outdoors over indoors.”

Q: What do recent studies say?

Respiratory viruses are transmitted in three main ways:

First, contact transmission:

This is where someone comes into direct contact with an infected person or touches a surface that has been contaminated.

Second, through droplet transmission:

This involves both large and small respiratory droplets that contain the virus, which would occur when near an infected person.

Third, through airborne transmission:

This involves smaller droplets and particles that are suspended in the air over longer distances and time than droplet transmission.

Some of the document superspreader events:

#1. In July 2020, a church choir singer in Australia was able to infect several others from a distance of more than 15 metres indoors, according to A recent study published by the U.S. Centers for Disease Control and Prevention,

#2. In September 2020, a second CDC-published study found an infection occurred in a New Zealand quarantine hotel i after an exposure time of less than a minute in an open doorway.

#3. In Quebec City,a gym where physical distancing and mask use were not enforced, has been linked to more than 500 COVID-19 cases and become one of the largest recorded superspreading events in Canada.

Q: What does science actually say about aerosol transmission?

Canada’s CBC News spoke to Dr Conly following the Calgary university forum. Once more, Dr Conly stressed that the way the virus transmits is "very complex" and that the "majority" of transmission occurs through “close contact.”

"Social distancing, or physical distancing as some call it, and hygiene, cleaning and disinfection of surfaces. That's where our focus should be," he said. "The science about how it's transmitted and where it goes, it will get itself sorted out."

Interestingly, Dr Conly authored a recent preprint study (funded by the WHO) refuting the notion aerosols are a primary mode of spread for the virus — due to "the lack of recoverable viral culture samples" from the air, which "prevents firm conclusions on airborne transmission."

Another Canadian scientist, Dr Raymond Tellier, disagrees. “The science is very strong to support aerosol transmission," said Tellier, an infectious diseases specialist and medical microbiologist who is also an associate medical professor at McGill University in Montreal. "We keep having example after example, and the objections are becoming increasingly unconvincing."

Moreover, Canadian epidemiologist Dr. David Fisman led a group of researchers that published a comment in The Lancet calling into question Dr Conly’s conclusion. Fisman’s camp presented several reasons for the primacy-of-airborne-transmission thesis including:

  • Superspreading events
  • Long-range infections
  • The higher risk of indoor transmission
  • The fact that virus particles have been detected in the air

The paper concludes that casting doubt on airborne transmission of the virus amounts to "scientific error" and that there is "consistent, strong evidence" that it spreads via aerosols, which are "likely to be dominant" over droplet and surface transmission.

Q: Do masks retain CO2, and decreases oxygen in pregnant women?

Other scientists, among them epidemiologists and infectious diseases physicians, say the role of aerosol transmission has been “underestimated”, at the very least. At the very most, it has been dangerously “downplayed”.

Australia’s chief medical officer, Prof Paul Kelly said: “There is no question, and never has been a question, right throughout this pandemic that aerosols do play a part in the transmission of this virus.” This was particularly the case indoors when many people were positive with the virus and in places with inadequate ventilation – such as some hotel quarantine facilities.

Q: What is the incubation period of the coronavirus disease?

The “incubation period” of COVID-19, the time between exposure to the virus and symptom onset, is on average 5-6 days, but can be as long as 14 days. Most experts prescribe quarantine period of 14 days from the last exposure to a confirmed case.

Q: How long does the coronavirus survive on surfaces?

According to WHO, there is no confirmed timeline how long a COVID-19 virus survives in surfaces. However, most likely it behaves like other coronaviruses. Studies show that coronaviruses can survive on surfaces for a few hours up to several days depending on varied conditions (e.g. type of surface, temperature or humidity of the environment).

Q: Can I get the coronavirus disease from swimming in a swimming pool?

Swimming in a well-maintained, properly chlorinated pool is safe. However, it is advisable to stay away from all crowded areas including crowded swimming pools. Keep 1 metre distance from people who sneeze or cough even in a swimming area.

Q: Is the coronavirus disease transmitted by direct contact?

One respiratory droplet from a COVID-19 positive person can contain thousands of viruses. There's ample evidence that the virus is transmitted through direct contact with droplets of an infected person (generated through coughing and sneezing). Individuals can also be infected from and touching surfaces contaminated with the virus and touching their face (e.g., eyes, nose, mouth).

The debate now raging between intellectual rival groups of scientists, however, is more nuanced. It's the primacy of droplets vs airborne. In October 2020, the US CDC updated its guidance to include the fact that COVID-19 can sometimes be spread via airborne transmission. The CDC also updated its guidelines to say the risk of COVID-19 infection from surfaces is now officially considered low.


The debate now raging between intellectual rival groups of scientists, however, is more nuanced. It's the primacy of droplets vs airborne. In October 2020, the US CDC updated its guidance to include the fact that COVID-19 can sometimes be spread via airborne transmission. The CDC also updated its guidelines to say the risk of COVID-19 infection from surfaces is now officially considered low. It's an acknowledgement that the risk of airborne transmission of the coronavirus is high.

Some scientists thinks it's embarrassing for WHO that they are pushing the droplet model so hard.

“If you don't include airborne, how are we in the middle of the global pandemic?” said Kimberly Prather, an atmospheric chemist and aerosol scientist at the Scripps Institution of Oceanography in San Diego, California. "How do you explain outdoor versus indoor? How do you explain superspreader events? How do you explain everyone that shares the room and never touches each other or gets close to each other gets infected? I mean, you can't."

"This virus travles in the air. Not rockes science," she commented.

If you don't include airborne, how are we in the middle of the global pandemic? How do you explain outdoor versus indoor? How do you explain superspreader events? How do you explain everyone that shares the room and never touches each other or gets close to each other gets infected? I mean, you can't."

- Kimberly Prather, atmospheric chemist and aerosol scientist at UC San Diego, California

"The evidence just keeps coming in every day ... there has not been a single paper that has pointed out why it isn't aerosols," she said. "The fact that the [WHO] is not just shouting that from the mountaintops to save lives is, quite frankly, disappointing."

Q: Can the coronavirus disease be transmitted in hot or humid climates?

From the evidence so far, the COVID-19 virus can be transmitted in all areas, including areas with hot and humid weather.

Q: Given these studies, will indoor air codes and building codes need to be updated?

For restaurants, movie houses, etc, some experts are proposing building code updates to prevent, or limit the spread of infectious diseases. There's no end in sight for the primacy of COVID-19 airborne transmission, yet there had been numerous documented superspreader events. It may take some time before a code tweak for indoor air may be adopted by different jurisdictions.


July 4, 2020:

More than 200 experts called for the WHO it to update its messaging on the threat of the spread of the coronavirus through the air. The WHO cited a lack of "definitive" evidence. In an open letter, 239 scientists from 32 countries called on the UN agency to acknowledge that airborne transmission of the coronavirus is a potential driver of the pandemic. The WHO stopped short of revising its messaging.

July 8, 2020:

The WHO's technical lead on the pandemic, Maria Van Kerkhove, said the agency's guidelines on airborne transmission are primarily focused on hospitals. Some experts say that statement doesn't go far enough to inform the public about the potential threat of the virus through the air.

April 9, 2021:

Dr. John Conly, top adviser to WHO and chair of the world body’s Infection Prevention and Control Research and Development Expert Group for COVID-19, said that N95 masks can cause "harms" — including acne — and pointed to a lack of “scientific evidence” for airborne transmission as the predominant means of COVID-19 infection.

April 25, 2021:

The US Centers for Disease Control and Prevention reported that the risk of surface transmission of COVID-19 is lower compared to airborne transmission — and people who obsessively disinfect surfaces may be doing more harm than good.

A “dogma” is any belief held unquestioningly and with undefended certainty.

Droplet dogma is the insistence, mainly by mainstream WHO scientists, that COVID-19 infections are primarily triggered by droplets, instead of airborne.

As early as July 2020, a group of 239 scientists from 32 countries already wrote an open letter calling on the world health body to update its messaging on the risk of airborne transmission of the coronavirus.
Days after the letter, the WHO amended its guidelines letter and acknowledged the possibility that aerosols can lead to outbreaks of COVID-19 in places such as choir practices, restaurants and fitness classes.

In October 2020, the US CDC also updated its guidance to include that COVID-19 can sometimes be spread via airborne transmission. The CDC also updated its guidelines to say the risk of COVID-19 infection from surfaces is now officially considered low.

This means disinfecting groceries, wiping down packages and cordoning off playgrounds are likely unnecessary.

The WHO has yet to do so.

“If you believe in evidence-based medicine and accept that measles has airborne transmission, it’s irrational and inconsistent to argue against airborne transmission of Covid,” Dr Daya Sharma stated in a tweet. “Droplet dogma is literally risking lives, & will make this pandemic harder to control.