Stopping the Superspreader

The case now for air quality & taming the most risky spaces

Michael Herf
5 min readJul 22, 2022


Image copyright The Associated Press

It’s the middle of 2022, and most folks in the US have given up COVID mitigations. Big conferences, indoor dining. It’s basically over, despite record rates of transmission and new variants on the horizon. Why did people stop every mitigation earlier this year, rather than picking some halfway mark? Well, because nobody agrees what this halfway mark is.

Here’s a place to start. At this moment, I think we should work the most to stop superspreader events, and I think the best ways to do this include two things: fixing indoor air quality, and finding the highest-risk areas (the worst 5–10%) so that improvements can be made.

Trevor Noah welcomes the press to the Correspondents Dinner, “The Nation’s Most Distinguished Superspreader Event” — which was, in fact, a superspreader event. (NBC)

Focusing on air quality and some particular crammed-in situations would help reduce transmission and disease a lot over the next few years.

Swiss Cheese? A great model, now too thick

The “Swiss cheese model” of COVID prevention has been extremely important. But we should recognize that it is too much for most people, since it appears to require that you do ten things, while changing your every behavior. I know, that’s not what it means, but people are acting like all these layers are, well, a big block of cheese. It’s time to remember that we can pick one or two layers and still make a difference.

For a lot of people, “layered mitigations” is confusing, as it includes being isolated from friends and family, not being able to keep a job and pay rent, a whole lot of vigilance and inconvenience. It’s too much, and what we need right now is to pick the most important layers. In addition to vaccines, there are several that happen in the background, and they don’t require continued vigilance.

Making the indoors more like outdoors

The easiest and best opportunity is indoor air quality. Sure, if you’re going to share bites of your meal with someone who’s very contagious, or talk for hours from close distance, there is a risk no matter what.

But everyone knows that doing things outdoors is “safer” than indoors, and why is this? It’s because the air is diluted outdoors — it moves up into the sky and mixes with a huge volume before anyone else breathes it.

When we go to work, or to an event, we have a kind of learned helplessness about the spaces we visit. We can’t change the building, so we don’t try. By the time we show up, it’s often too late to do anything but wear a mask.

And certainly, a huge number of things can’t be done outdoors — in the middle of summer, the winter, or during a rainstorm, or when you need a projector to show your trade-secret Powerpoint. So we continue to have lots of meetings in rooms with no ventilation, people continue to take public transit in badly ventilated spaces, and classes are almost always indoors, without upgrades to improve air quality.

Dilution to fix superspreaders

At a big event with a super-infectious person, if you’re sitting right next to that person, you’re at high risk. It’s just the way it is.

But when using ventilation or filtration to dilute the air, 100:1 or 1000:1, you can prevent most infections just 5–10 feet away, making it so your event (or your office) gets two people sick rather than 25. If your CO2 meter says 2000 ppm, you’re breathing a lot of other people’s air, and if it says 500 ppm (just a bit over the 420ppm outdoors), you’re doing a lot better.

Why would we give up this layer? It makes no sense. It is relatively cheap to add some ventilation to your party or indoor space, and it’s an easy fix.

People don’t control their buildings, but they can ask — early on

Walking into a crowded room with low ceilings, there’s not much you can do. This is why people need to ask early on: can we put some filters here, or leave the doors open? It doesn’t take very much.

Also, funding matters, and it has to happen over time. Federal funding to upgrade air quality has reached some schools, though mainly schools have treated it as a capital improvement (a one-time cost) rather than an ongoing cost (electricity, filters, maintenance) and this funding remains more rare than it should be. Regardless, it’s important to recognize that upgraded air has ongoing costs, even if these costs are relatively low per person.

In most conference venues, classrooms, and workplaces, upgraded air filtration is not usually on the list of benefits, the list of things people feel empowered to ask about or change.

But if more people ask for this, especially earlier on? It will get better.

Finding the riskiest places, and labeling them

We need ways to assess buildings, buses, rooms, and other places. While we inspect some restaurants to see if they have rats or safe food handling, we do not routinely inspect spaces for air quality.

We could even devise a visible label that shows a space meets some basic level of performance, explaining that the owners have upgraded filters, or use a fresh-air return for mechanical ventilation. For extra confirmation, we can look to Belgium’s policy of including CO2 meters in many spaces as an extra level of confirmation.

We should look for whole categories (like public transit, offices, or classrooms) that may require upgrades to have safer air. Perhaps unventilated buses could remind people to wear masks or to crack the windows.

Stop the superspreader by fixing the air

We need to do these new mitigations at low cost to the economy, and they must even benefit the reluctant — ventilation does not impede your ability to do what you want. It’s clear with vaccines having a smaller effect than expected on transmission that we need another layer or two for now.

A real target could be superspreaders, and one of the most consistent and simple ways to help is by fixing indoor air.



Michael Herf

co-founder of f.lux, finding the connections between circadian rhythms, sleep, healthy buildings, and light. (Previously made Picasa.)