CDC school reopening guidance suppresses aerosols based on thin evidence and driven by budgetary concerns

For a period of time after this article was originally published (February 18, 2021) it was scrubbed from Google’s search index. When the author, Lambert Strether, realized the piece had been “censored,” it was published a second time on March 1, 2021 with an analysis of the purging. Subsequently, the article magically reappeared in the search index. —Eds.

The CDC, newly headed by Biden appointee Rochelle Walensky, has issued guidance on school re-opening. From the Associated Press:

The Centers for Disease Control and Prevention released its long-awaited road map for getting students back to classrooms in the middle of a pandemic that has killed nearly 480,000 people in the U.S. But the agency’s guidance is just that — it cannot force schools to reopen, and CDC officials were careful to say they are not calling for a mandate that all U.S. schools be reopened.

Officials said there is strong evidence now that schools can reopen, especially at lower grade levels….

The guidance was issued as President Joe Biden faces increasing pressure to deliver on his promise to get the majority of K-8 schools back to in-person teaching by the end of his first 100 days in office. He acknowledged that the goal was ambitious, but added, “It is also a goal we can meet if we follow the science.”

This post will follow the science; it’s an open question, however, whether CDC did, as we shall see. There are two key documents:

1. Operational Strategy for K-12 Schools through Phased Mitigation (“Strategy“) (updated Feb. 12, 2021), which provides guidance to the schools, and
2. Transmission of SARS-CoV-2 in K-12 schools (“Transmission“) (updated Feb. 12, 2021), which documents “the science” upon which the guidance is (putatively) based. (Readers may wish to jump to the Appendix, where Table 2 lists, categorizes, and provides quotations from the 61 sources cited in Transmission. Scanning the quotations may provide an approximation of the science as CDC understands it, at least with respect to Covid, schools, and children. I will use select citations from Table 2 in Table 1, when I take a look at CDC’s use of epidemiogy.)

There are two central issues with Strategy. The first might be labeled its Central Dogma. The second is the action items in Strategy. Here is the CDC’s Central Dogma:

The occurrence of SARS-CoV-2 infection in schools reflects transmission in the surrounding community.

That is, schools themselves are not drivers of transmission, but rather, as it were, passive recipients of it. This is certainly disputable, for example in this recent thread on Montréal:

6) Dr. Drouin noted that Montreal schools have become a driving force in the spread of the #coronavirus since reopening last month, blaming them for the increase in #COVID19 cases among the 0-to-17 and 35-to-44 age demographics, the latter being parents.

— Aaron Derfel (@Aaron_Derfel) February 11, 2021

See also this recent thread on the UK:

Let's look at the trends of infection in different age groups in England first- as reported by the ONS. Being a random survey of infection in the community, this doesn't suffer from the biases of symptom-based testing, particularly important in children who are often asymptomatic

— Deepti Gurdasani (@dgurdasani1) February 18, 2021

I will have more to say about reasoning from other countries to this one later in the post. But for now, consider these two tweets as prima facie evidence that the CDC’s Central Dogma is open to question. We will pass on from that topic to the central focus of this post: The CDC’s action items. From Executive Summary of Strategy, here they are:

You will notice immediately that aerosol transmission is omitted; the message of Strategy is that aerosol transmission can be ignored because it is not an “essential” element. This message is getting through; from an acute summary of Strategy in WaPo, “The CDC’s plan to reopen schools seems to prioritize expediency over teachers’ health“:

Here’s what the guidance does well. Unlike the Trump administration’s watered-down recommendations that were couched in language such as wearing masks “if possible,” these new guidelines are clear on many points. They lay out five mitigation measures that every school should implement: masking, distancing, hand-washing, cleaning and contact tracing. The part I like the most is how the CDC has divided schools into four categories based on degree of covid-19 transmission in their surrounding communities. At low and moderate levels, full in-person learning can occur; at higher levels, hybrid or reduced attendance is recommended.

Again, the CDC’s “mitigation strategies” omit discussion of aerosol entirely (even to ventilation). Frankly, I was gobsmacked. I hate to deploy terms like “criminal malpractice,” so I won’t, but such was my level of gobsmacked-ness. Further, if you accept, as I do, the SARS-COV-2 can be transmitted by aerosols, the CDC Transmission document—“the science” backing up the recommendations—rests on a very modest epidemiological base. Let’s consider first the CDC’s suppression¹ of aerosol transmission.

The CDC Suppresses Aerosol Transmission: Why?

First, let’s define our terms. From an excellent article in Journal of Hospital Infection, “Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)“:

There is little doubt that SARS-CoV-2 is transmitted via a range of airborne particle sizes subject to all the usual ventilation parameters and human behaviour. To clarify the terminology used in this article, therefore, droplets are particles that fall to the ground (or any surface including vertical surfaces) under the influence of gravity and/or the momentum of an infected person’s exhaled air; and aerosols are particles that remain suspended due to size and/or environmental conditions.

I would summarize this by saying that particle behavior is what matters, not arbitrary size constraints. Aerosols float, like cigarette smoke. Droplets are ballistic; they fall, like tiny loogies. Hence, whenever you hear somebody advocating a distance measure, like the six feet recommended by Strategy, you’re hearing someone protecting against droplets, but notaerosols, because aerosols can float for long distances. Aerosols, again like cigarette smoke, gradually fill up any closed space into which they are emitted. El Pais has an especially vivid discussion of this in “A room, a bar and a classroom: how the coronavirus is spread through the air“:

(The figures are based on the Covid Airborne Transmission Estimator developed by a group of scientists led by Professor José Luis Jiménez from the University of Colorado.) I saw that El Pais article cited innumerable times on the Twitter by people reacting to CDC’s aerosol-suppressing guidance, so I imagine at some point the CDC and the White House will become aware of it.

Now, to be fair, aerosol vs. droplet transmission has been a bit of a paradigm shift for the public health community (con vs. pro)². However, until CDC Strategy came out, I had thought that aerosol transmission was settled science; that the shift had occurred. El Pais once more:

In the spring, health authorities failed to focus on aerosol transmission, but recent scientific publications have forced the World Health Organization (WHO) and the CDC to acknowledge it. An article in the prestigious Science magazine found that there is “overwhelming evidence” that airborne transmission is a “major transmission route” for the coronavirus, and the CDC now notes that, “under certain conditions, they seem to have infected others who were more than six feet [two meters] away. These transmissions occurred within enclosed spaces that had inadequate ventilation. Sometimes the infected person was breathing heavily, for example, while singing or exercising.”

Now, however, the CDC is backsliding; of the many institutions and publications supporting aerosol transmission I”ll pick Harvard’s T. H. Chan School of Health, since Walensky is surely familiar with it:

4/ The decision to open schools is complex, controversial, & emotional. Everyone wants students & teachers to be safe. The gist of all reputable reports on school re-opening is a layered approach, but critical to address the airborne component of spread. https://t.co/aQTHnv57w7

— Dr. Alex Huffman (@HuffmanLabDU) February 13, 2021

But why the backsliding? (Walensky’s message discipline is such that she didn’t mention either aerosols or ventilation in her interview on Face the Nation.) I believe the answer is to be found in the source cited in the very first footnote of our second document, Transmission. From The National Academies of Sciences, Engineering, and Medicine, “Reopening K-12 Schools During the COVID-19 Pandemic: Prioritizing Health, Equity, and Communities,” at section “The Role of Airborne Transmission of COVID-19“:

In the process of writing this report, the committee repeatedly returned to conversations around the role of airborne transmission of COVID-19. As described in Chapter 3, indoor air quality in U.S. public schools is notoriously poor, which can have innumerable deleterious health impacts on students and staff. However, because there is not yet scientific consensus on the role of airborne transmission in the spread of the virus, it is also unclear how the indoor air quality of schools matters in the spread of COVID-19. Given the considerable cost associated with updating aging facilities, it is particularly important to understand the exact role of airborne transmission such that stakeholders can assess the relative value and utility of that investment.

Needless to say, this is a budgetary — hence political — constraint, not “the science.” Nor could it be! And sadly, by reducing the question of aerosol transmission and indoor quality to facilities they enable the CDC to deny children, parents, and teachers simpler methods of mitigation:

4/ Unless I missed it, zilch on engineering controls such as improved centralized filtration (just in case you can't do that ventilation thing). Incredibly disappointing.

— Dr. Richard Corsi (@CorsIAQ) February 13, 2021

Shoddy work all round.

The CDC’s Epidemiology Is Weak

Now let us turn to “the science,” as presented in Transmission. Let me explain why, while I respect the other methods of scientific work being done Covid — statistical work, aggregater reports, metastudies, and miscellaneous narratives — I find epidemiological studies — wiht index cases, seating diagrams, contact tracing — essential. For a policy maker, no doubt all the methods listed are important. But for me as an individual, they are not enough. A metaphor may help. For a World War I General asking his soldiers to go “over the top,” a likely casualty rate will have informed his decision. But the soldier needs to know the actual ground; where the barbed wire is, when to duck the machine gun fire, etc. With Covid, I would want to know the actual ground, too, no matter the odds: For example, I know it makes no sense to sit downwind from an air conditioner in a closed space, even if it makes sense to enter the closed space in the first place. Only “shoe leather” epidemiology can provide such answers. For example, I would certainly want to know whether the windows in my child’s classroom could be opened, if they can be, whether they are.

However, epidemiology, being of the ground, is necessarily localized and not global. For example, here is a description of schooling in Norway from an American who spent a year as a teacher there.

After every 45 min or so of lessons, students spend 10 to 15 minutes playing outside or in common areas– as many as five or six times a day. At many schools teachers hold on to the students’ cell phones all day in a “cell phone hotel” and encourage real play during break times, like a short pick-up game of soccer or foosball or just jumping around with friends for a few minutes. And during this time, someone always opens a window to let in a little fresh air, even in December.

Obviously, that’s a well-ventilated school (and one that dilutes any aerosols that are to be found). And yet, I doubt very much whether any of the global, statistical work that includes data from Norway takes these facts on the ground into account. How would they now? And yet, given that aerosol transmission is “the science,” those facts are essential. With that in mind, let us look at all the epidemiological studies in Transmission, extracting the relevant rows from Table 2 in Appendix 1:

Table 1: Epidemiological Sources in CDC’s Transmission of SARS-CoV-2 in K-12 schools

You will observe there are 14 epidemiological cases in all. Recalling the example of Norway above, we throw out all the examples except those from the US. Four remain, which I have helpfully highlighted. Two are gyms, which are nothing like classrooms in their patterns of ventilation, both in Florida (!). One is a choir room, ditto. One remains.

Therefore, as far as school re-opening classroom epidemiology in the United States goes, Transmission depends on one case. Transmission is an enormous inverted pyramid whose apex is a single point. I have to say that balancing act doesn’t fill me with confidence.

Conclusion

Politico summarized the CDC’s reopening strategy in “Biden’s follow-the-science mantra on school meets political reality“:

Biden administration officials insist that the White House is grounding all of its policy decisions firmly in the best available evidence. They say the president receives a daily state of pandemic update from his Covid response team in his daily briefing book. And indeed, the Biden administration has taken care to give health experts like Anthony Fauci and CDC Director Rochelle Walensky leading roles in managing the response, and solicited constant input from its health agencies and outside public health groups.

Well, no. The budgetary concerns of “stakeholders” aren’t science, aren’t a mantra, and aren’t evidence, either. If Biden’s response team isn’t including aerosols and ventilation in his briefing books (the same issue occurs in other contexts) I want to know why. Ditto for soliciting constant input, because it doesn’t look like CDC reached out to aerosol experts at all. And then Politico continues:

Biden transition officials spent weeks crafting plans for safely reopening schools based on public health best practices, including proposing a massive new Covid testing regime and hundreds of billions of dollars in funding to help retrofit classrooms and overhaul ventilation systems.

No, they didn’t, because without taking aerosol tranmission into account, you don’t havebest practices; you have tepid guidance like opening windows “to the extent possible.” But even more weirdly, if overhauling ventilation systems is going to be a line item in the budget, why in the name of all that is holy did CDC carefully suppress aerosols from its guidance? Or fail to do any serious epidemiological work on it?

The CDC already has two strikes against it: It catastrophically butchered the test kit rollout³, and it butchered the software development for VAMA (the Vaccine Administration Management System). Now Walensky whiffs on school re-opening. Is that strike three? It’s hard to avoid the conclusion that the CDC is completely dysfunctional, and that Walensky, despite her warm personality, is unlikely to have the administrative and institutional chops to fix what’s wrong.

Notes

1. ↩ The CDC does mention ventilation in its “Health Facilities” section: “Improve ventilation to the extent possible such as by opening windows and doors to increase circulation of outdoor air to increase the delivery of clean air and dilute potential contaminants.” Sounds discouraging. Nor is aerosol tranmission mentioned. Why then open the windows?
2. ↩ Here is an entertaining thread on the history of droplets v. aerosols from that same Professor Jiménez.
3. ↩ Of the many shifting stories, here is the latest.

APPENDIX

Table 2: Complete Sources in CDC’s Transmission of SARS-CoV-2 in K-12 schools

Legend:

The Note column keys to the footnote numbers in SARS-CoV-2 in K-12 schools.

Abbreviations by column: Method: Model, Statistical, Epidemiological, Aggregation, Metastudy Narrative; Type: Article, Editorial Letter Revview Study Status: Preprint, Fininal, Other.

Citations are to linked title and publication only, for space purposes.

Beneath each source row, I’ve placed a quotation taken from that source. Scanning the quotes may give a sense of where “the science” is, as CDC conceives it.