Here’s why aerosol transmission of COVID matters to us all

by Raywat Deonandan

This article was published in The Ottawa Citizen on Oct 19, 2021.


Eighteen months into the pandemic, we continue to learn about COVID-19 transmission. While there is still some disagreement, it’s becoming clear that so-called aerosol transmission is an important and overlooked infectious route.

There are at least five ways that viruses can infect people: via (1) vectors, like mosquitoes that bite an infected person then transfer infection to a new person via another bite; (2) the oral-fecal route, which is exactly what it sounds like; (3) direct contact, such as sexual intimacy; (4) so-called “fomite” transmission, in which an infected person touches a doorknob or other object, which is subsequently touched by another person who then acquires that infection; and (5) via large droplets, which are small bits of exhaled fluid, typically larger than 5 microns, which gravity drags harmlessly to the ground within 1-2 metres.

COVID-19 is not known to be vectorborne. And while traces of the SARS-CoV2 virus have been found in the feces of infected people, oral-fecal transmission has not been observed. The same is true for sexual contact: the virus has been detected in the semen of infected men but has never been observed to infect others through sexual fluids.

Early on, there was panic around the prospect of fomite transmission, with many people disinfecting their groceries and mail. While there is some evidence for fomite transmission, cases are vanishingly rare and are definitely not the means by which COVID has stifled the world.

Instead, public health officials contend that large droplets are the primary infection route. Hence the reliance on social distancing, plexiglass barriers, and simple masks, which serve as “windbreaks” that shorten the distance that droplets can travel.

However, since at least summer of 2020, it was becoming clear to many scientists that COVID-19 has a significant aerosol transmission component. Aerosols are small droplets that can be 1-5 microns or even smaller, and that can linger in the air for hours. People naturally produce respiratory aerosols by several means, including breathing, talking, and coughing. Some medical procedures, like CPR and tracheotomy, can artificially generate them, as well.

Whereas large droplets are responsible for short range transmission and are typically what we see in diseases like influenza, aerosols are responsible for the long range transmission that we see in Measles and Chickenpox, and now COVID.

One way to visualize aerosol transmission is to think about cigarette smoke, which is made up of aerosol particles 0.1-1 microns in diameter. Imagine a COVID-infected person exhaling a cloud of such “smoke”. See how it floats out from the creases of a poorly-fitted mask and over the tops of plexiglass barriers. See how it’s thickest nearer to its source, but still present many metres further away. Notice how it lingers for hours in an enclosed space, even after its source has left the premises.

Aerosol transmission explains some of the deeper mysteries of this pandemic. Transmission between people who have never been in the same room, as in occupants of quarantine hotels or cruise ships, can now be explained by their shared ventilation systems.

With the reality of aerosol transmission comes the need to invest in different mitigation tools. Droplet dogma holds that poorly fitted surgical masks and social distancing are sufficient to slow most population spread. But aerosols are best controlled by ventilation and high quality fitted masks, such as N95 respirators.

One could argue that controlling droplet transmission is largely the burden of the people, who are responsible for wearing masks and keeping their distance. But controlling aerosols is more the responsibility of government and employers: providing N95 masks to forward-facing staff, and requiring good ventilation in schools and workplaces.

To safely navigate out of this pandemic, we must acknowledge the significance of aerosol transmission and take the appropriate mitigation steps. This means a focus on well fitted, high quality masks and proper indoor ventilation.

Raywat Deonandan is an Epidemiologist and Associate Professor with the Faculty of Health Sciences, University of Ottawa.

Vaccinating Children Should Be Encouraged… But Not Compelled. Not Yet.

By Raywat Deonandan
July 15, 2021

This article was published in The Ottawa Citizen on July 15, 2021.

Is there any more touchy pandemic subject than whether parents should vaccinate their children? The idea of injecting my own infant with a relatively new pharmaceutical product when he is otherwise fit and healthy does not fill me with joy. On the other hand, in case you hadn’t heard, there is an epidemic of a virulent respiratory disease afoot, one that is known to torment, disable and even kill children, however rarely. Surely I would want to protect my child from the insidious SARS-Cov2 virus?

The risk vs reward computation when it comes to vaccinating children is not an easy one. As best we know, the risks posed by the COVID vaccine are vanishingly small, but not zero. A tiny proportion of vaccinated children experience serious, though treatable, adverse events, like myocarditis (heart muscle inflammation).

Meanwhile, trials show an astonishing vaccine efficacy of 100% among children. But the reward of offering protection against COVID is admittedly small, as children are thought to be less likely to suffer from symptomatic COVID; though some do become hospitalized and die.

About 11% of COVID cases in Ontario are experienced by children, though they comprise 19% of the population. And so far in this province, only one child death is thought to have been caused by COVID. But one is too many. And the delta variant is painting a new picture, in which increases in serious pediatric cases are being seen in the USA.

So if the personal risk and personal reward are both small, how does one decide? For many, the tie-breaker is the reward to society: getting a significant step closer to herd immunity. With the delta variant ascendant with its hyper-transmissible nature and slight challenge to vaccine effectiveness, the threshold for achieving herd immunity has been pushed quite high indeed, to the point where if only Canadian adults were to be immunized, we likely would not have enough resistant bodies to get the job done. Vaccinating children becomes an important strategic move to get us closer to something resembling herd immunity.

Absent high levels of population immunity, we will experience recurring outbreaks mostly among unvaccinated groups. Since schools are finally becoming understood as both essential services and contributors to community transmission, we certainly do not want preventable outbreaks occurring in schools. So it makes sense to want to maximize vaccine uptake among all eligible school children.

This brings up a very divisive policy question: should COVID vaccines be made compulsory for school children? Ontario already requires that children attending schools in person must be immunized against nine infections, including tetanus and diphtheria. COVID vaccination, being one of the most efficient strategies for limiting an acute public health crisis, could rationally be added to that list.

But the 1990 Immunization of School Pupils Act allows for exemptions due to “conscience or religious belief”, which could presumably encompass a wide array of mindsets. Given the high prevalence of vaccine hesitancy among parents, the number choosing the exemption option could be substantial, putting in doubt whether mandatory vaccination would indeed render a substantial increase in population immunity.

My fear is that making this particular vaccine mandatory for children would not only be rejected by a skittish population, but would inadvertently strengthen the narrative of those wishing to characterize public health as insidious authoritarian government overreach. It would set back our efforts to win over hearts and minds to unite Canadians behind our battle against COVID.

Absent compelled vaccination, we must endeavour to educate parents and walk them through individualized risk-reward analyses, presenting evidence for both transparently. And accommodation can be explored for those who will not, or cannot, be vaccinated. This can include remote learning options or a stringent requirement for frequent testing.

Parental hesitancy is fueled by fear, misinformation and apathy. Making vaccination compulsory addresses the apathy, but accentuates the fear and strengthens the credibility of misinformation. The danger in legislating any public health compliance is in inadvertently increasing the behaviour that we seek to suppress.

Compelling vaccination for children –COVID vaccination specifically, given its charged political nature– has its own risk-reward ratio. While it might inch us closer to herd immunity and safer schools, it might also push wavering parents toward hardcore anti-vax camps, impairing our ability to enact deeper public health improvements in the long term. Let us cajole, educate, and incentivize rather than bludgeon parents with the brute force of the law. In the end, reason and caring must win out.


Let’s clear up the confusion over talk of a ‘preferred’ vaccine

by Raywat Deonandan
May 5, 2021

This article was published in The Ottawa Citizen on May 5, 2021.

I’m fond of citing a paper from 2007 about lessons learned from SARS that we should apply to the next pandemic. Its number one recommendation was that there should be transparent communication between all parties, including to the public. And yet this is where we have stumbled throughout every step of this emergency.

The latest such stumble comes from NACI (the National Advisory Committee on Immunization), who stated that the mRNA vaccines (Pfizer and Moderna) are “preferred” but that those who “do not wish to wait” for an mRNA could accept one of the viral vector vaccines — AstraZeneca or Johnson & Johnson — if “the benefits outweigh the risk for the individual.”

NACI’s role is to quantify risk and reward with respect to vaccination, and to advise decision-makers via the Canadian Immunization Guide, which is a guidance document meant for use by health-care professionals and vaccine program managers. In times of pandemic, however, NACI’s words are being parsed and interpreted in real time by an audience with whom the committee had never before had to deal directly: the general public.

Communicating with the public is starkly different from offering guidance to health-care professionals. Words such as “preferred vaccine” are, frankly, triggering, and introduce an element of classism into the fracas. Who mostly got the “less preferred” vaccine? Essential workers. Poor people. Racialized people.

Predictably, those Canadians who had dutifully accepted the AstraZeneca vaccine, after having been told by health leaders to “get the first shot that is offered,” feel betrayed. As someone tweeted to me, it’s like the Boomers made GenX take all the risks while keeping “the good stuff” for themselves — like wanting others to eat the no-name cookies before opening up the Oreos for themselves.

I have four immediate thoughts about this latest episode in the ongoing daytime soap opera that is our vaccine rollout and its endless communication missteps.

First, it’s important to take a moment to appreciate what an astonishing thing it is to have a choice of which life-saving vaccine to accept in the middle of a deadly pandemic. Most parts of the world don’t have that luxury. So while the government messaging is often confusing, let’s be thankful for the luxury of that confusion.

Second, “preference” isn’t simply a matter of choice. It’s also a matter of circumstance. The AstraZeneca jab is in many ways the vaccine of the world. It is inexpensive, easily made (compared to the mRNA doses), and can be transported and stored with less consternation. For many parts of the globe, it is the preferred vaccine as it will drag large populations out of this crisis.

Similarly, the Johnson & Johnson vaccine famously only requires one dose, so is ideal for the homeless, the nomadic, or migrant workers — any group for whom scheduling the second dose could be difficult, if not impossible. Clearly, for them J&J would be the preferred vaccine.

Third, preference and choice are luxuries not only for those with access to multiple formulations, but also to those who can afford to wait for their favoured brand. Many communities in Canada cannot wait. Hot-zone neighbourhoods, essential workers, and poor and racialized people who are at great risk of COVID infection cannot afford to wait.

Maybe you prefer Perrier to tap water, but when you’re dying of thirst, you’d best take the first glass of water offered.

Fourth, those Canadians who received the AstraZeneca vaccine should not feel cheated or coerced. Every day spent unvaccinated is a day in which they could have contracted COVID and possibly be fighting for their lives in an ICU ward. This is especially true if they live in a hot zone or are essential workers.

The lesson from all of this, as it has been from the very beginning, is that the pandemic is all about equity. Some groups are more likely to be exposed and infected, to be rendered unemployed, to be hospitalized and die, to lack access to a vaccine, and now to be unable to wait for a “preferred” vaccine, however problematic and incorrect that term might be. Ill-considered messaging does not alleviate the strain of inequity, and might indeed serve to exacerbate it.

There are no second-class COVID vaccines in Canada. They all get the job done.


Raywat Deonandan is an Epidemiologist and Associate Professor with the Faculty of Health Sciences, University of Ottawa.

COVID-19: Exponential Growth and the Myth of the Balanced Response

by Raywat Deonandan

April 27, 2021

A slightly modified version of this article was published in The Ottawa Citizen with the title, “Deonandan: COVID-19 — How Ontario fell into the myth of the balanced response” on April 28, 2021.

Earlier this month, Ontario’s Solicitor General Sylvia Jones was asked on a radio show why the province waited so long before enacting the COVID-19 restrictions that doctors and scientists had been pleading for. Earlier, Ontario’s Science Table had observed a worrying growth trend in cases and ICU usage and had forecasted a dire and explosive situation just mere weeks away.

Jones replied, “We wanted to make sure that the modelling was actually showing up in our hospitals.”

This was a curious answer that speaks to the heart of the issue of slow and ineffective government responses to the pandemic. It is also why the so-called “balanced response” advocated by those seeking to calibrate public health responses against real-time data was always doomed to failure.

The problem, simply, is exponential growth. Most of us do not understand it. In a pandemic, that failure of understanding is our undoing.

Investors know it as compound interest. Consider the unlikely but delectable scenario in which you pay a single dollar into an investment fund that guarantees to double your money every three days. How long will it be before you become a millionaire? You might be shocked to know that it would only take sixty days. That is the insidious magic of exponential growth.

Similarly, a small number of COVID-19 cases can explode into a nightmarishly overrun healthcare system in a matter of weeks. If you wait until you see the modelling in the hospitals, it is probably too late to prevent the crisis.


The human brain thinks naturally in terms of linear growth, possibly developed through millennia of evolution chasing prey and escaping from predators who tend to move at constant speeds over a given period. It is why we can easily predict where a vehicle or a running animal will cross our path if it does not change course or accelerate.

But we struggle to internalize exponential growth, which can be deadly when responding to an infectious disease. A 2020 paper by German statisticians suggested that, “people mistakenly perceive the coronavirus to grow in a linear manner, underestimating its actual potential for exponential growth.” The authors go on to say that this cognitive failure, “influences political opinions about matters of life and death.”

Exponential growth comes in two phases. As labelled by author Richard Baldwin, the first is the “imperceptible progress” phase and the second is “explosive progress”. In the first phase, growth is acknowledged but easily dismissed. But in the second phase, we are overwhelmed by growth and act surprised that it is happening at all.


Futurist Roy Amara lends his name to Amara’s Law, which states, that “we tend to overestimate the effect of a technology in the short run and underestimate the effect in the long run.” This is because technologies tend to grow exponentially, and we salivate over their unrealized potential early on –the imperceptible progress phase– but are shocked when that potential is actualized and overwhelms us in the explosive progress phase.

For example, the growth in the speed of computers in the past couple of years has been twice that of the previous fifty years. Baldwin argues that that is why Artificial Intelligence suddenly seems so daunting, though its rate of development has been steadily on an exponential curve for years.

We can see Sylvia Jones falling into the trap of Amara’s Law. By waiting to see if the explosive growth of COVID-19 shown by the provincial modelling would manifest in the hospitals, the province was in essence doing nothing during the “imperceptible progress” phase of the 3rd wave. So here we are, overwhelmed in the “explosive progress” phase.

The lesson of exponential growth as it pertains to public health is this: When we know it is happening, when we are still in the “imperceptible progress” phase, we must act decisively. If we wait until the “explosive progress” phase, we risk not having the resources to mount a sufficient response.

In other words, our response must always feel like a premature overreaction, or else it will never be enough.

Raywat Deonandan is an Epidemiologist and Associate Professor with the Faculty of Health Sciences, University of Ottawa

No, you shouldn’t wait for a better vaccine

by Raywat Deonandan

Mar 15, 2021

This article was published in The Ottawa Citizen under the title, “Deonandan: No, you shouldn’t wait for a better vaccine” on Mar 15, 2021.

Scientists were rendered giddy by the data published by Pfizer and Moderna for their COVID-19 vaccines. Each showed 94-95% efficacy! Canadians now have access to formulations from Astra Zeneca and Johnson & Johnson, as well. But their efficacy scores, while very good, are nonetheless slightly lower than those of Pfizer and Moderna So some Canadians are choosing to wait for “a better option” when given the chance to receive an AZ or J&J shot immediately. Continue reading

The Saturday Debate: Can the Tokyo Olympics still happen this summer?

by Raywat Deonandan & Helen Lenskyj

Jan 23, 2021

This article was the “No” component of a two-side debate. The “yes” side was written by Dick Pound. This debate was published in The Toronto Star on Jan 23, 2021.


In March 2020, the International Olympic Committee (IOC) reluctantly and belatedly announced the decision to postpone the 2020 Tokyo Olympics to July 2021. Since that time, organizers have addressed the challenges of doing so — in most cases, inadequately. Continue reading

Delaying That Second Dose Is Not Evidence-Based Medicine But It Still Makes Sense

by Raywat Deonandan

Mar 5, 2021

This article was published in The Ottawa Citizen on Mar 5, 2021.


The clinical trial data describing the safety and efficacy of the Pfizer and Moderna COVID vaccines were probably the most scrutinized science papers in history. They showed efficacy scores over 94% when a prime dose was followed by a booster 21 or 28 days later. Yet the National Advisory Committee on Immunization (NACI) now recommends extending that interval to up to 4 months, a substantial deviation from the manufacturers’ directions. This has upset many who feel that this departure is tantamount to experimentation without consent. Continue reading

Wearing a face mask is both socially responsible and self-interested

by Raywat Deonandan

This article was published in The Ottawa Citizen on July 14, 2020. It was adapted from a blog post titled, “COVID19: Heroes Wear Masks.”

In many cities, each night at dusk, grateful residents applaud health care workers. It’s a reminder that in the early phase of the COVID-19 pandemic, doctors and nurses held the front line. All that was required from the rest of us was to stay home, watch Netflix, and learn to bake.

Continue reading

COVID19 Testing is Our Salvation

by Raywat Deonandan

This article was first published in India Currents Magazine on April 7, 2020. It is based on this blog post.

We are weeks into widespread social distancing in many parts of the world, though it feels like months. Cases of COVID19 continue to mount, as expected, and we watch Italy and Spain for signs of when our society might be cast into crisis and chaos. Health care workers, the heroes of our time (and of all times, really), gird themselves for a flood of respiratory distress cases, projected to peak sometime in April. Physicians and nurses of all specialties are being asked to update their ventilator training in anticipation of being called to the front lines for service. Yet many fear that they will not have sufficient weapons for this fight, such as masks and ventilators.

At this time, it’s important to remember that COVID19 has a global case-fatality rate of about 2 to 3%lower in the USA, meaning that most people will survive this. In the words of Larry Brilliant, “this is not a zombie apocalypse. It’s not a mass extinction event.” What is it, then? This is, and always has been, a health systems crisis more than simply a health crisis. Continue reading

COVID-19 is not a health crisis, it is a health systems crisis

by Raywat Deonandan

This article was published in The Toronto Star on April 7, 2020. It is based on an earlier blog post.

Most models of the COVID-19 pandemic show it continuing for another year or two, with North America stifled beneath the current wave of cases until June at the earliest. With such harrowing realities, it’s easy to mischaracterize this crisis as solely a medical one. Continue reading