Coronavirus transmission: SARS-CoV-2 in the air

When the Covid-19 pandemic first began, most people focused on the risk of catching the new coronavirus from touching surfaces. Fast-forward to today, and it’s clear that SARS-CoV-2 is most often spread via droplets and aerosols floating in the air. Yet, says Joe Allen of the Harvard T.H. Chan School of Public Health, too much effort and money are still being spent on cleaning as opposed to investing in better indoor ventilation and filtration systems. That’s one of a number of missteps in the US response to the pandemic. In this interview, Allen describes how to make buildings healthier in the battle against Covid. This is the first episode in Knowable’s new video series: Reset: The Science of Crisis & Recovery.

READ MORE: The Fluid Dynamics of Disease Transmission, Annual Review of Fluid Mechanics 2021

This video is part of Reset: The Science of Crisis & Recovery, an ongoing series exploring how the world is navigating the coronavirus pandemic, its consequences and the way forward. Reset is supported by a grant from the Alfred P. Sloan Foundation.

Video Transcript:

Joe Allen: “This will surprise people. We don’t have a single documented case of transmission from contaminated surfaces. The reality is this is an airborne virus. We’re focusing our attention on the wrong risk — surfaces — and not focusing our attention and resources on where the real risk is, and that’s airborne transmission.”

Covid: First line of defense

Joe Allen (director, Harvard School of Public Health Healthy Buildings Program): “So the story of Covid, in my view, is one of a series of missteps. We actually knew what to do very early on. There was this early fear that maybe this virus was spread through surfaces and that led to, in my opinion, over-response towards cleaning surfaces. One of the problems with focusing too much attention on surface transmission is that many organizations — I’ve worked with homeless shelters, schools — have been spending all their time and money on addressing the risk through surface contamination, as opposed to spending that time and money focusing on the real risk, which is through the air — which means they should be focusing on things like ventilation and filtration. There are even reports of some schools that are closing for an entire day for deep cleaning. So that doesn’t make any sense to me from a real exposure and risk standpoint. It’s not doing anything to protect the adults and students. It might feel good, it might look good, but it’s actually hygiene theater.

YouTuber: “You’ve got to be putting that disinfectant on these groceries.”

Joe Allen: “There were YouTube videos with tens of millions of views telling people how to wipe and wash down every single item they bought at the grocery store.

Newscaster: “Covid outbreak at a spin class.”

Joe Allen: “But in reality, every high-profile outbreak — be it spin class, on a school bus, choir practice — they all share the same fundamental characteristics: time spent indoors, no masks and low to no ventilation. Every single time.”

Newscaster: “A Washington choir practice turns deadly.”

Joe Allen: “So by not acknowledging that this virus travels through the air, I think it was a big failing.”

Newscaster: “Tonight, researchers around the world say the evidence shows the new coronavirus is likely airborne.”

Joe Allen: “My entire field has been sounding the alarm on this. Two hundred thirty-nine of us wrote a letter to the World Health Organization, bringing our collective voice from our field together to urge them to recognize that airborne transmission was happening, and therefore recommend that people add ventilation and filtration to the list of things and measures they’re already doing like mask-wearing.

“So it’s been totally shocking and a gross failing, in my view, that it’s taken a year for CDC and others to recognize that this was important. We knew a year ago healthy buildings needed to be the first line of defense against this novel coronavirus.”

Healthy building: Strategies and controls

Joe Allen: “We do know about how to keep people safe from infectious diseases indoors. I’m coming from a background doing forensic investigations of sick buildings, so this might be a cancer cluster, an office building, disease outbreak in a school, and through that experience we know what controls are needed to keep people safe in any indoor environment, be it from a radiological hazard, a chemical hazard, a physical hazard, or in this case with Covid a biological hazard. We know how to assess a hazard, we know how to put in appropriate controls to keep people safe — things like higher ventilation rates, better levels of filtration, reducing the occupancy or de-densifying our buildings.”

Respiratory aerosols: Understanding the science

Joe Allen: “So it’s impossible to know why there’s so much hesitancy by CDC and WHO and others, but some of it ties back to a fundamental misunderstanding of respiratory aerosols. This goes back to the outdated medical literature showing that respiratory aerosols — when we talk, breathe or sing — settle out of the air within six feet. The reality is these aerosols will travel beyond six feet and they’ll stay aloft for hours. In fact, they’ll accumulate indoors, both at close contact and at distance, unless they are diluted out of the air through ventilation or cleaned out of the air through filtration. And so we knew all of this early on and every piece of evidence since last winter has further validated that hypothesis.

“We know from basic aerosol physics that these particles will stay aloft. We have air-sampling data showing viable virus detected well beyond six feet. We have epidemiological evidence. We’ve known this for a long time in my field — building science, indoor air quality science, aerosol science — but largely that hasn’t penetrated into the medical literature.

“Many people early on and even today are failing to do these basic control measures like rolling down your window in the car to bring in fresh outdoor air, or doing that at home if someone is sick, or in an office building or a school, bringing in more outdoor air to dilute the buildup of these respiratory aerosols.

“What we’ve been recommending is achieving four to six air changes per hour through any combination of better ventilation or filtration. That means you can open up your windows to bring in more outdoor air, or run your mechanical system at a little bit higher speeds to bring in more outdoor air. When it’s too cold and the windows have to be closed, you can compensate by using better filters. So if you have a mechanical system, you want a higher grade filter on the recirculated air. And if you don’t have that, you can use a portable air cleaner with a HEPA filter. These are plug-and-play devices that can give you four or five or six air changes per hour very quickly and for relatively low cost.”

Surface transmission: The basics

Joe Allen: “Surface transmission — it’s called fomite transmission. A fomite is any surface that can act as a source of transference. Fomite transmission can happen; it’s just not happening a lot. That doesn’t mean we let our guard down when it comes to surfaces — cleaning, disinfection is important, particularly in high-risk contexts like health-care settings — but for the average person, the way to break that transmission chain is just through handwashing and using hand sanitizer frequently. Yes, it’s OK to accept the package that was delivered to your door, or that if you get groceries you don’t need to wipe down everything. You simply put them away and wash your hands when you’re done.

Indoor environment: Major impact on our health

Joe Allen: “We spend 90 percent of our time indoors, and like it or not we’ve become an indoor species. And when we think about it this way it becomes obvious and even intuitive that the indoor environment has an outsized impact on our health. Covid has ushered in this new appreciation, or awareness anyway, of just how much time people are spending indoors. For many people they are essentially locked down in their home, and others who are out and have to be at work are recognizing that the way these — our manufacturing facilities, our hospitals — the way these are designed determine whether or not they’re getting sick.

Newscaster: “There are new fears over meat-packing facilities where workers continue to get sick.”

Joe Allen: “The researchers in this healthy building or indoor air quality space — that has exploded, and that’s a good thing. Who is going to go back to a building right now that isn’t a healthy building? Covid was an all-in moment for the world, and the US has failed in our first year. In terms of healthy buildings, I hope this pandemic catalyzes the movement such that we no longer have buildings and health be a secondary aspect to our approach to the way we design and operate our built environment. We have to have health as core and fundamental to our decisions that we’re making around our schools, homes and offices. And it’s been an afterthought. We’ve been stuck in this sick-building era, and my hope as we move into this healthy-building era, where the focus is the health of all people in all buildings everywhere, every day.”