The Air Quality Op-Ed I meant to write

So, you may remember a very recent quick hit #13:

13) Local school/air quality news, “NC parents are buying air purifiers for schools. Are they worth the cost to fight COVID?”

Last school year, Wake County school system installed MERV-13 air filters in the HVAC units at each school. But the district is only providing individual air purification units to special-needs classrooms where students are unable to wear face masks.

The reason that Wake County hasn’t provided air purifiers in every classroom is the ABC Science Collaborative, a group formed by Duke University to advise schools on COVID issues.

“Air exchange, purifiers, or filters may help minimally, but have not been shown to help if people are masked.”

I’ve been meaning to write a whole post about this, but, what the hell?!?!  There’s plenty of evidence, just no large trials.  A lack of large RCT trials is not the same things as “no scientific data.”  This is just wrong.  

I had really thought about writing an Op-Ed about this.  And, honestly, if I wasn’t so busy on various strains of Covid research, I would have.  But, hey, fortunately, a group of NC State Engineering professors wrote a terrific Op-Ed, putting to shame all the people in my alma mater in the ABC collaborative.  This is really good:

The most recent research shows COVID-19 is primarily transmitted through aerosols, tiny particles emitted to the air as we exhale. These aerosols linger for hours and pose a risk to people in an indoor space long after an infected person has left. A recent study by leading researchers concludes that adopting a layered approach to risk mitigation is the best way to navigate the pandemic.

Unfortunately, this evidence has not reached local authorities. In a recent N&O article, we were dismayed to read that ABC Science Collaborative claims “There are no scientific data to support that the use of HEPA filters and ventilation work to prevent spread of COVID-19 when everyone is masking.” This statement appears to be based on an outdated and limited study conducted last winter, before classrooms were full and the far-more-infectious delta variant became the dominant form of this coronavirus.

Since then, several studies have confirmed that aerosol-removing air filtration units reduce the risk of transmission in classrooms…

We fully support mask mandates, but they alone are not a silver bullet. As any parent or teacher can attest, kids’ attention to proper mask wearing is imperfect at best. Thus, other layers of protection are essential. Air filtration should be used as a complement to enhanced building ventilation.

As scientists and concerned parents, we implore WCPSS to do two things:

1. Keep pace with the latest in our scientific understanding of COVID.

2. Act quickly to implement low cost, low risk solutions equitably.

Many of the additional layers of protection come with multiple benefits, such as the use of improved air filtration long-term to keep school air healthy, and spending more time outdoors. These investments can improve our schools for many years to come.

Very good stuff.  Had I written the Op-Ed, I probably would have tried to include this from a July CDC report that the ABC folks chose to ignore:


What is already known about this topic?

Ventilation systems can be supplemented with portable high efficiency particulate air (HEPA) cleaners to reduce the number of airborne infectious particles.

What is added by this report?

A simulated infected meeting participant who was exhaling aerosols was placed in a room with two simulated uninfected participants and a simulated uninfected speaker. Using two HEPA air cleaners close to the aerosol source reduced the aerosol exposure of the uninfected participants and speaker by up to 65%. A combination of HEPA air cleaners and universal masking reduced exposure by up to 90%.

What are the implications for public health practice?

Portable HEPA air cleaners can reduce exposure to simulated SARS-CoV-2 aerosols in indoor environments, especially when combined with universal masking.

Anyway, it still kind of astounds me that public health professionals would advocate masks as a single magic bullet and ignore the layered risk reduction approach basically every serious person has been advocating.  And in schools with sub-optimal ventilation, air filtration should almost sure be part of that layered risk reduction.  

About Steve Greene
Professor of Political Science at NC State

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