Is air filtration the best public health intervention against respiratory viruses?


This transcript has been edited for clarity.

When it comes to the public health fight against respiratory viruses – COVID, flu, RSV, and so on – it has always struck me as strange how staunchly basically any intervention is opposed. Masking was, of course, the prototypical entrenched warfare of opposing ideologies, with advocates pointing to studies suggesting the efficacy of masking to prevent transmission and advocating for broad masking recommendations, and detractors citing studies that suggested masks were ineffective and characterizing masking policies as fascist overreach. I’ll admit that I was always perplexed by this a bit, as that particular intervention seemed so benign – a bit annoying, I guess, but not crazy.

I have come to appreciate what I call status quo bias, which is the tendency to reject any policy, advice, or intervention that would force you, as an individual, to change your usual behavior. We just don’t like to do that. It has made me think that the most successful public health interventions might be the ones that take the individual out of the loop. And air quality control seems an ideal fit here. Here is a potential intervention where you, the individual, have to do precisely nothing. The status quo is preserved. We just, you know, have cleaner indoor air.

But even the suggestion of air treatment systems as a bulwark against respiratory virus transmission has been met with not just skepticism but cynicism, and perhaps even defeatism. It seems that there are those out there who think there really is nothing we can do. Sickness is interpreted in a Calvinistic framework: You become ill because it is your pre-destiny. But maybe air treatment could actually work. It seems like it might, if a new paper from PLOS One is to be believed.

What we’re talking about is a study titled “Bipolar Ionization Rapidly Inactivates Real-World, Airborne Concentrations of Infective Respiratory Viruses” – a highly controlled, laboratory-based analysis of a bipolar ionization system which seems to rapidly reduce viral counts in the air.

The proposed mechanism of action is pretty simple. The ionization system – which, don’t worry, has been shown not to produce ozone – spits out positively and negatively charged particles, which float around the test chamber, designed to look like a pretty standard room that you might find in an office or a school.

courtesy PLOS One

Virus is then injected into the chamber through an aerosolization machine, to achieve concentrations on the order of what you might get standing within 6 feet or so of someone actively infected with COVID while they are breathing and talking.

The idea is that those ions stick to the virus particles, similar to how a balloon sticks to the wall after you rub it on your hair, and that tends to cause them to clump together and settle on surfaces more rapidly, and thus get farther away from their ports of entry to the human system: nose, mouth, and eyes. But the ions may also interfere with viruses’ ability to bind to cellular receptors, even in the air.

To quantify viral infectivity, the researchers used a biological system. Basically, you take air samples and expose a petri dish of cells to them and see how many cells die. Fewer cells dying, less infective. Under control conditions, you can see that virus infectivity does decrease over time. Time zero here is the end of a SARS-CoV-2 aerosolization.

courtesy PLOS One

This may simply reflect the fact that virus particles settle out of the air. But when the ionization system was added, infectivity decreases much more quickly. As you can see, within about an hour, you have almost no infective virus detectable. That’s fairly impressive.

courtesy PLOS One

Now, I’m not saying that this is a panacea, but it is certainly worth considering the use of technologies like these if we are going to revamp the infrastructure of our offices and schools. And, of course, it would be nice to see this tested in a rigorous clinical trial with actual infected people, not cells, as the outcome. But I continue to be encouraged by interventions like this which, to be honest, ask very little of us as individuals. Maybe it’s time we accept the things, or people, that we cannot change.

F. Perry Wilson, MD, MSCE, is an associate professor of medicine and public health and director of Yale’s Clinical and Translational Research Accelerator. He reported no relevant conflicts of interest.

A version of this article first appeared on

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