In-School Prevention

Data to inform COVID-mitigation strategy in your school.

Smoke rising. Just like breath does.
Image by Brigitte makes custom works from your photos, thanks a lot from Pixabay.
Distance isn’t what matters.
What matters is masking, ventilation, occupancy,
and time.
(CNBC, 04.23.2021)

Once you’re wearing a mask, distancing doesn’t matter so much, because masks block most large droplets. What matters, according to this study from MIT, is how many people are in the room, how well ventilated it is, and how long you spend there.

Even if your classrooms are this old-fashioned, your ventilation systems shouldn’t be. Photo by Jeffrey Hamilton on Unsplash.
Designing infectious disease resilience into school buildings
through improvements
to ventilation and air cleaning
(The Lancet COVID-19 Commission on Safe Work,
Safe School, and Safe Travel, 04.2021)

Don’t worry, it’s shorter than the title makes it seem – only five pages of content plus references. Includes five big takeaways:

  • Have pros check buildings and their ventilation systems regularly.
  • Ventilate with clean outdoor air.
  • Improve buildings’ air-cleaning efficiency using methods that aren’t snake oil.
  • Use portable air cleaners with HEPA filters if you have to.
  • Consider other strategies as long as there’s good evidence that they work – like UVGI systems.
A blacklight bulb.
Image by TheLight from Pixabay.
If you’ve got high ceilings, UVGI can keep your air cleaner. (Science Daily, 11.20.2020)

UVGI is shorthand for Ultraviolet Germicidal Irradiation, and it actually does work, because UV light kills viruses. However, it also can harm people, so you don’t want to bathe the whole room in it while folks are there.

Solution: Install UVGI units up near the ceiling. People breathe out viruses –> their warm breath rises up to ceiling level –> UVGI units zap viruses. Cool, huh?

School SMART graphic from the Harvard T.H. Chan School of Public Health’s Healthy Buildings campaign. Make it your mantra.
How to Improve Ventilation
On the Cheap

While we wait for government funds to cover major-league improvements to school ventilation, there are quick, inexpensive things we can do to decrease the likelihood that SARS-CoV-2 particles are contaminating classroom air. This list of “hacks” from CovidStraightTalk can help.

Want to buy portable air filters for your classrooms? This doc, developed by the San Francisco Department of Public Health, tells you everything you need to know. Should you even bother buying them? What does all the jargon mean? What kind should you buy? Once you’ve got them, where should you put them? It’s all spelled out.

Only want to buy filters that have FDA approval specifically for removing coronavirus? Here you go.

Do we really need 6 feet of distance if we’re all wearing masks?
(One True Thing, 03.10.21)

Honestly, the answer is no, as long as the other safety measures are in place. For a version of this article that can be customized for your school, click here.

This Ohio district has kept kids in person all year with three feet of distancing and no in-school transmission, thanks to strict mask rules. An Indiana district mentioned in this article let kids who were between 3 and 6 feet of COVID-positive classmates stay in school – and infection rates didn’t rise.

Those stories are just anecdotal evidence, I grant you. But this study from the journal Clinical Infectious Diseases isn’t. It followed over 500K K-12 students and nearly 100K staff members for 16 weeks in the fall of 2020. All the schools required masks, and 90% of them had improved their ventilation in some way. There was no significant difference in the COVID rates between schools that kept folks at 3 feet of distance and those that kept folks 6 feet apart. NB: This study was done when the virus variants had not yet hit the US.

Should kids who’ve been 3 – 6 feet away from one another be considered close contacts?
(The Ohio Schools COVID-19 Evaluation Research Team, 01.29.21)

This report from a big consortium of universities, hospitals, and research centers says no, as long as everyone involved was wearing masks.

As they explain, “Children who were close contacts and appropriately masked had rates of COVID-19 that were similar to children with no known COVID-19 exposure in school. The COVID-19 rate in the comparison group suggests community transmission outside the school

In other words, kids weren’t getting COVID from the kids they sat next to in school – they were getting it when they weren’t in school.

CDC logo.
Operational Strategy
For K-12 Schools Through Phased Mitigation
(CDC Guidance, 02.12.21)

Wear a knotted-and-tucked surgical mask (or a surgical mask under a 3-layer cloth mask). Keep your distance (6 feet or more whenever possible). Wash your hands. Keep a clean, ventilated school. Use contact tracing. Use cohorts or pods. Screen for COVID if possible, prioritizing areas hard-hit by infections. This should all sound pretty familiar by now, but it’s nice to finally hear it in no uncertain terms from on high. The ABC Science Collaborative in North Carolina has published a great explanation of how to operationalize these recommendations.

Not sure why more emphasis wasn’t placed on ventilation, but were you really expecting perfection? C’mon. At least we *have* national guidelines now.

Person in mask with virus particles. Image by Tumisu from Pixabay.
Wear Masks, Use Good Filters,
and Open the Windows

Ok, the CDC does care about ventilation, too. Here are their recommendations for schools and childcare settings. If you’re wondering what they recommend, read the headline above this paragraph.

If you want much more detailed advice, go to the WHO’s Roadmap to Improve and Ensure Good Ventilation in the Context of COVID-19 and scroll to p. 23 (non-residential settings).

If you’re a visual learner, check out the NY Times’ animation on how ventilation dilutes coronavirus-carrying aerosols in a classroom.

Two Apps to Help Maximize Classroom Safety

How long can 15 students safely stay in a 900-square-foot classroom while masked, seated, and talking? How about 20 students in a 1200-square-foot classroom? This app, from fluid dynamics researchers at MIT, lets you input your school’s parameters to find out what works.

According to this model of COVID-19 aerosol transmission from the Max Planck Society, opening windows every hour, having everyone wear masks, and decreasing the number of students from 25 to 12 took the probability of infection in a classroom from 90% to 12%. You can enter parameters for your own rooms and see how your risk changes.

Cleaning supplies. Image by congerdesign from Pixabay
Still Disinfecting Surfaces?
It Might Not Be Worth It

“In hospitals, surfaces have been tested near COVID-19 patients, and no infectious virus can be identified. . . . because the virus is very fragile in the environment —
it decays very quickly.” (WBUR, 12.28.20)

“Hand washing is crucial . . . because surface transmission can’t be ruled out. But it’s more important to improve ventilation systems or to install air purifiers than to sterilize surfaces.” (Nature, 01.29.21)

Image by elizabethaferry from Pixabay
One Type of Indoor Area
Is Especially High-Risk
For COVID-19

(Inverse, 12.15.20)

A study found that “moving people leave behind a floating bubble of virus-laden droplets or a trailing, virus-containing cloud. In a narrow corridor, this cloud becomes concentrated — posing more danger to those coming behind than it otherwise would in a larger, open-air space.” Take-home message: ventilate your corridors as well as you can!

Massachusetts General Hospital logo
MGH Covid-19 School and Community Resource Library

The mother lode of scientific resources for schools and communities, aggregated by the Division of Infectious Disease at Massachusetts General Hospital. Intended for use by school physicians. Continuously updated.

Image by Rose Wong, NY Times; adapted from Ian M. Mackay ( and James T. Reason
The Swiss Cheese Model
Of Pandemic Defense

(NY Times, 12.05.20)

“The Swiss Cheese Respiratory Pandemic Defense recognizes that no single intervention is perfect at preventing the spread of the coronavirus. Each intervention (layer) has holes.”

But combine several layers, and you have a really good barrier. The trick is you need all those layers together, not just one.

Image from Kwon KS et al.
Six Feet of Distance Isn’t Enough
If the Airflow Is Right

(LA Times, 12.09.20)

Thanks to Korea’s unparalleled contact tracing, this study was able to show how an unmasked restaurant diner was infected in 5 minutes from more than 20 feet away.

Why does this matter for schools? Because if you’re serving meals, six feet of distance between your students may not be enough. (emphasis added)

Calendar. Image by tigerlily713 from Pixabay.
New Science Suggests How to Shorten Quarantine
(Elemental/Medium, 11.10.20)

Testing upon exit of quarantine — ideally around day six or seven — is more effective than upon entry, and testing twice could make an eight-day quarantine as effective as a 14-day one.

Some 2-Week Coronavirus Quarantines Can Be Cut to
10 or 7 Days

(Boston Globe, 12.02.20)

The CDC shortened its recommended quarantine duration – not because the science has changed, but because they’d rather have people quarantine for a week or 10 days than not at all.

Mask with “no COVID” symbol. Image by mohamed Hassan from Pixabay.
Concrete Evidence That Masks Help Keep Schools Safe (ProPublica, 11.24.20)

This article focuses on two Georgia school systems – one where a mask mandate was instituted, and one without a mask mandate. Their different outcomes highlight the need to follow CDC guidance on COVID-19 precautions.

Homemade mask. Photo by JAJA DO on Unsplash.
Masks Work. Really. We’ll Show You How (NY Times, 10.30.20)

With coronavirus cases still rising, wearing a mask is more important than ever. In this animation, you will see just how effective a swath of fabric can be at fighting the pandemic.

Risk Assessment and Testing Protocols for Reducing
SARS-CoV-2 Transmission
in K-12 Schools

The Rockefeller Foundation’s report aims to help school administrators assess the risk of SARS-CoV-2 (the virus that causes Covid-19) in their schools, and identify key considerations in developing a screening

CDC logo.
Screening After Covid Recovery (10.29.20)

Student tests positive –> student quarantines –> student comes back to school. Should this student be part of COVID screening now?
Answer: The student should be excluded from COVID screening for 90 days after the positive test.

NEA Educating Through Crisis

Information on teachers’ rights and responsibilities during the pandemic, how to ensure equity for students, and teaching skills and strategies. Also includes resources for families.

Dear Pandemic: School

A team of researchers and clinicians answers questions about Covid-19. This link goes to the school section of their website.


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