ExclusivesThinkingDr Joseph Allen: “Our buildings have the power to combat COVID-19”

Respiratory aerosols account for around 90% of COVID-19 transmission. Dr Joseph Allen explains why better ventilation and filtration is the answer…
Sophie Barton2 months ago11 min

“Imagine we’re sitting near one another and I’m smoking a cigarette,” says Dr Joseph Allen. “You’ll get a big dose of my smoke. If you’re on the far side of the room, you’ll smell the smoke, but the dose you inhale will be less. And if it’s a well-ventilated space, you might not even know I’m smoking at all.”

You may wonder what the build-up of cigarette smoke has to do with COVID-19, but it makes a great analogy for the airborne transmission of the virus. While it is passed on via larger respiratory droplets, emitted when an infected person coughs, talks or breathes, it is also transmitted through tiny respiratory droplets called aerosols. They are so small they staying floating in the air, travel further and accumulate in poorly ventilated indoor spaces. And like larger respiratory droplets, they also infect people when inhaled.

“We estimate that respiratory aerosols account for 90% or more of COVID-19 transmission,” explains Dr Allen, who is one of the world’s leading experts on healthy buildings. “That’s around 60% of near-field transmission and around 40% of far-field transmission, so beyond 6ft.

“Imagine you’re in a small room, with typical ceiling height and low ventilation and you have a smoker in there smoking for hours. They are releasing respiratory aerosols for hours and that’s going to build up. Ultimately, you’re going to be exposed. And that is why ventilation and filtration are so important.”

Inadequate ventilation and filtration

As many of us return to our workplaces, it’s a valuable lesson to learn. However, the harsh reality is that many of the buildings we occupy have inadequate ventilation and filtration. And their ability to stop – or spread – the virus has been underrated in the fight against COVID-19.

“Buildings can either keep us safe, or aid in the spread of disease,” says Dr Allen. “And there’s no doubt that the power our buildings have to fight this virus has been underestimated.

“Many people have also underestimated the potential for buildings to aid the spread of COVID-19. In every single outbreak, we see the same three factors – indoors, no masks and low-level ventilation. Whether it’s a restaurant, bus or gym class, it doesn’t matter. It’s when those three factors line up that you have a problem.

“The build-up of respiratory aerosols will happen in indoor, under-ventilated spaces or places with poor filtration. Imagine someone is smoking a cigarette five week away from you outdoors – you might not even notice, because there’s unlimited ventilation.”

A weapon against COVID-19

While the vaccination programme may be romping on apace, infections are rising in countries across the globe and we live under the constant shadow of new variants. So, are we in danger of woefully underusing buildings as a weapon against COVID-19?

“In offices, homes and aeroplanes we’ve designed our air quality standards to bare minimums that aren’t designed for health,” warns Dr Joesph Allen. “When I do forensic investigations of sick buildings, problems come up like tiredness, headaches and even serious issues like cancer clusters. And inevitably the ventilation system plays a role.

“Not only are we designing for a minimum, non-health-based standard but rarely are our buildings even meeting that. They change over time and they don’t change for the better – the filtration doesn’t improve, it gets worse.

“It’s a massive problem, but throw in a pandemic and you have a recipe for absolute disaster. Not only do we know that ventilation and filtration are important, but most building aren’t even close to reaching the standard they should for reducing infectious disease transmission.”

Consider an alternative scenario for a second. What if, 40 years ago we had designed all the spaces we occupy to a healthier building standard?

“Every building, every school would now be designed to a higher standard,” says Dr Allen. “And the pandemic would be less of a problem. The super spreader events are all tied to under ventilated places, where the filters are poor.”

Investment pays

So, what’s stalling this need for better indoor air quality standards? One misconception is cost, an argument Dr Joseph Allen puts to rest in his landmark book, Healthy Buildings. Over time, employee health problems and lower productivity come at a vastly higher price.

He says, “There’s a perception that healthy buildings are expensive, but they’re not. Actually, sick buildings are expensive. But we tend to think of the energy costs or the upfront costs, without contemplating the human health and productivity costs. Actually, the benefits far outweigh the cost by orders of magnitude.

“Another issue is that decisions are usually made at the facilities level, which is not necessarily responsible for thinking about infectious disease or productivity. If your job is to focus on controlling the energy budget, you might not think about health.”

However, Dr Joesph Allen says he is finally sensing a long-awaited shift in the tide.

“There has been an awakening, but it’s been slow – we’re now 16 months into this,” he says. “We have been talking about the power of buildings since January 2020 and it’s only in the past couple of months that it’s been more widely accepted and officially recognised by bodies like the World Health Organisation and the US CDC. It took a remarkably long time, but I’m optimistic now.

“COVID has brought the deficiencies in our buildings into C-suite conversation too. Previously, a CEO might have been thinking about their portfolios, but not too much about air quality. But now that’s changing, because now every CEO is enquiring about the status of their building. They’ve had to, and this will change the nature of the conversation going forward.”


Dr Joseph G. Allen is Director of the Healthy Buildings program and Associate Professor at the Harvard T.H. Chan School of Public Health. He is also Chair of the Lancet COVID-19 Commission Task Force on Safe Work, Safe Schools, and Safe Travel.

For more content from Dr Joseph Allen, click here.  

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Dr Joseph Allen

Sophie Barton

Sophie Barton is our Features Editor. She a journalist and editor with 17 years’ experience in the national media, specialising in wellbeing and lifestyle.

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