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CDC School Reopening Guidance Suppresses Aerosols Based on Thin Evidence and Driven by Budgetary Concerns

Summary:
By Lambert Strether of Corrente. 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

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By Lambert Strether of Corrente.

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:

See also this recent thread on the UK:

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:

CDC School Reopening Guidance Suppresses Aerosols Based on Thin Evidence and Driven by Budgetary Concerns

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 suppression[1] 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 not aerosols, 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“:

CDC School Reopening Guidance Suppresses Aerosols Based on Thin Evidence and Driven by Budgetary Concerns

(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:

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:

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

45 Finland Epi School Art Ot 07/30/20 Transmission of SARS-CoV-2 following exposure in school settings: experience from two Helsinki area exposure incidents. Preprint. MedRxiv
When the index was a child, no school transmission was identified, while the occurrence of an adult case led to a 16% AR. Further cases were evidenced in 3 families, but other transmission chains were plausible. It is likely that transmission from children to adults is limited.
60 France Epi Choir Room Art Fi 12/23/20 High Rate of SARS-CoV-2 Transmission Due to Choir Practice in France at the Beginning of the COVID-19 Pandemic. J Voice.
The characteristics of the viral transmission via close human contacts was probably enhanced by the act of singing, at a phase of intense circulation of SARS-CoV-2 in the population at this period. We report in our study the role of asymptomatic infection carriers initiating a silent chain of transmission of the coronavirus, leading to a cluster under the circumstances of the rehearsal. This study confirms that the transmission of the virus from asymptomatic cases is very efficient.
41 Germany Epi School/ECOC Art Fi 09/10/20 Transmission of SARS-CoV-2 in children aged 0 to 19 years in childcare facilities and schools after their reopening in May 2020, Baden-Württemberg, Germany. Euro Surveill.
Child-to-child transmission in schools/childcare facilities appeared very uncommon. We anticipate that, with face mask use and frequent ventilation of rooms, transmission rates in schools/childcare facilities would remain low in the next term, even if classes’ group sizes were increased.
23 Israel Epi Household Art Fi 08/2020 The Role of Children in the Dynamics of Intra Family Coronavirus 2019 Spread in Densely Populated Area. Pediatr Infect Dis J.
Our investigation demonstrated significantly lower rates of COVID-19 positivity in children compared with adults residing in the same household.
36 Israel Epi School Art Fi 07/23/20 A large COVID-19 outbreak in a high school 10 days after schools’ reopening, Israel, May 2020. Euro Surveill
The high school outbreak in Jerusalem displayed mass COVID-19 transmission upon school reopening. The circumstances promoting infection spread involved return of teenage students to their regular classes after a 2-month closure (on 18 May) and an extreme heatwave (on 19 May) with temperatures rising to 40 °C and above [6] that involved exemption from facemasks and continuous air-conditioning.
48 Italy Epi School/ECOC Art Fi 12/2020 Secondary transmission of COVID-19 in preschool and school settings in northern Italy after their reopening in September 2020: a population-based study. Euro Surveill
The overall secondary case attack rate was 3.2%, reaching 6.6% in middle and high schools. More timely isolation and testing of classmates could be effective in reducing virus transmission in this setting.
52 Norway Epi School Art Fi 01/2021 Minimal transmission of SARS-CoV-2 from paediatric COVID-19 cases in primary schools, Norway, August to November 2020
This prospective study shows that transmission of SARS-CoV-2 from children under 14 years of age was minimal in primary schools in Oslo and Viken, the two Norwegian counties with the highest COVID-19 incidence and in which 35% of the Norwegian population resides.
40 Singapore Epi School/ECOC Art Fi 06/25/20 Novel coronavirus 2019 transmission risk in educational settings. Clin Infect Dis.
The data suggest that children are not the primary drivers of SARS-CoV-2 transmission in schools and could help inform exit strategies for lifting of lockdowns.
55 South Korea Epi Fitness Center Art Fi 05/15/20 Cluster of Coronavirus Disease Associated with Fitness Dance Classes, South Korea. Emerg Infect Dis. 2020
During 24 days in Cheonan, South Korea, 112 persons were infected with severe acute respiratory syndrome coronavirus 2 associated with fitness dance classes at 12 sports facilities. Intense physical exercise in densely populated sports facilities could increase risk for infection.
56 South Korea Epi Fitness Center Art Fi 08/10/20 Epidemiological Characteristics of COVID-19 Outbreak at Fitness Centers in Cheonan, Korea. J Korean Med Sci
Zumba is an exercise fitness program which combines aerobic exercise with music, and Oriental and Latin dance moves.5 In the fitness centers where the Zumba classes were held, a large number of students had taken classes in a relatively crowded space, although ventilation systems were working properly. … [T]he droplets produced by exhalation or cough of a patient during the exercise have higher chance of reaching the nose, mouth or eye of other class participants directly, as well as remaining on the surface of the exercise equipment and later transmitted by contact.
57 US, FL Epi School Gym Art Fi 10/16/20 An Outbreak of COVID-19 Associated with a Recreational Hockey Game — Florida, June 2020. MMWR Morb Mortal Wkly Rep
The study was unable to determine exactly where exposure occurred, but hypothesizes it was at the evening hockey game, due to the heavy breathing that occurs, the lack of masks covering the mouth and nose, the transition from ice to bench where players continue heavy breathing or in the locker rooms and lack of other common exposures or time spent together.
58 US, FL Epi School Gym Art Fi 01/26/21 SARS-CoV-2 Transmission Associated with High School Wrestling Tournaments — Florida, December 2020–January 2021. MMWR Morb Mortal Wkly Rep
An outbreak arising from a Florida high school wrestling tournament in December 2020 had an attack rate of at least 30% (38 of 126 tournament attendees who were tested) and a secondary attack rate of at least 9% (41 of 441 close contacts of the 38 COVID-19 patients)
39 US, NC Epi School Art Pr 1/2021 Incidence and Secondary Transmission of SARS-CoV-2 Infections in Schools. Pediatrics.
In the first 9 weeks of in-person instruction in North Carolina schools, we found extremely limited within-school secondary transmission of SARS-CoV-2, determined by contact tracing
59 US, WA Epi Choir Room Art Fi 05/15/20 High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice — Skagit County, Washington, March 2020. MMWR Morb Mortal Wkly Rep.
Transmission was likely facilitated by close proximity (within 6 feet) during practice and augmented by the act of singing.

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 have best 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 rollout[3], 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.

Note Country Method Venue (Epi. Only) Type Status Date Citation
1 Agg Art Fi 07/15/20 Reopening K-12 Schools During the COVID-19 Pandemic: Prioritizing Health, Equity, and Communities. Consensus study report from The National Academies Press.
In its final recommendation, the committee identifies four areas of research that are urgently needed to fill the existing gaps in evidence: (1) the role of children in transmission of SARS-CoV-2, (2) the role of reopening schools in the spread of SARS-CoV-2 in communities, (3) the role of airborne transmission of COVID-19, and (4) the relative effectiveness of different mitigation strategies in schools.
2 Nar Edi Fi 07/29/20 COVID-19 and School Closures. JAMA
Given the strong connection between education, income, and life expectancy,9 school closures could have long-term deleterious consequences for child health, likely reaching into adulthood. School closures also affect parents’ ability to work.
3 Australia Sta Art Fi 09/25/21 COVID-19 in Victorian Schools: An analysis of child-care and school outbreak data and evidence-based recommendations for opening schools and keeping them open. Report from Murdoch Children’s Research Institute and the University of Melbourne. 2020; Published 2020 September 25.
Infections linked to [Early Childhood Education and Care (ECECs)] and schools peaked at the time when community transmission was highest during July and then declined in August, suggesting that infections in ECECs and schools are driven primarily by transmission in the broader community.
4 US Sta Art Fi 04/10/20 Coronavirus Disease 2019 in Children — United States, February 12–April 2, 2020. MMWR Morb Mortal Wkly Rep
[R]elatively few children with COVID-19 are hospitalized, and fewer children than adults experience fever, cough, or shortness of breath
5 Mod Let Fi 06/16/20 Age-dependent effects in the transmission and control of COVID-19 epidemics. Nat Med
We estimate that susceptibility to infection in individuals under 20 years of age is approximately half that of adults aged over 20 years, and that clinical symptoms manifest in 21% (95% credible interval: 12–31%) of infections in 10- to 19-year-olds
6 China Sta Art Fi 03/16/20 Epidemiology of COVID-19 Among Children in China. Pediatrics
Children of all ages appeared susceptible to COVID-19, and there was no significant sex difference. Although clinical manifestations of children’s COVID-19 cases were generally less severe than those of adult patients, young children, particularly infants, were vulnerable to infection.
7 US, UT/WA Sta Art Fi 01/01/21 Symptoms and Transmission of SARS-CoV-2 Among Children — Utah and Wisconsin, March–May 2020. Pediatrics.
Children and adults had similar secondary infection rates, but children generally had less frequent and severe symptoms. In two states early in the pandemic, we observed possible transmission from children in approximately one-fifth of households with potential to observe such transmission patterns.
8 US, UT/WA Sta Art Fi 01/01/21 COVID-19 in Children: Looking Forward, Not Back. Pediatrics
In this study, the researchers found that 20% and 17% of households had potential child-to-adult transmission and child-to-child transmission, respectively, but numbers are too small to draw definitive conclusions.
9 China Sta Let Fi 04/23/20 SARS-CoV-2 Infection in Children.NEJM
In contrast with infected adults, most infected children appear to have a milder clinical course. Asymptomatic infections were not uncommon.2 Determination of the transmission potential of these asymptomatic patients is important for guiding the development of measures to control the ongoing pandemic.
10 Agg Rev Fi 06/17/20 Children are unlikely to be the main drivers of the COVID‐19 pandemic – A systematic review. Acta Paediatr.
Children are unlikely to be the main drivers of the pandemic. Opening up schools and kindergartens is unlikely to impact COVID-19 mortality rates in older people.
11 Agg Rev Fi 12/2020 COVID-19 in children: current evidence and key questions. Curr Opin Infect Dis
Important questions remain unanswered regarding why children have mild disease compared with adults; how children of different ages contribute to asymptomatic community transmission of the virus; and the pathophysiology of and most appropriate investigation and treatment strategies for the novel hyperinflammatory syndrome.
12 Agg Rev 09/01/20 Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection in Children and Adolescents: A Systematic Review. JAMA Pediatr
The rapid spread of COVID-19 across the globe and the lack of European and US data on pediatric patients require further epidemiologic and clinical studies to identify possible preventive and therapeutic strategies.
13 Agg Rev Fi 04/06/20 Epidemiology and clinical features of coronavirus disease 2019 in children. Clin Exp Pediatr
This review summarizes what is currently known about COVID-19 in children and adolescents.
14 Agg Rev Ot 01/12/20 Why is COVID-19 less severe in children? A review of the proposed mechanisms underlying the age-related difference in severity of SARS-CoV-2 infections. Arch Dis Child.
In this review, we discuss proposed hypotheses for the age-related difference in severity of coronavirus disease
15 Europe Sta Art Fi 06/25/20 COVID-19 in children and adolescents in Europe: a multinational, multicentre cohort study. Lancet Child Adolesc Health
COVID-19 is generally a mild disease in children, including infants. However, a small proportion develop severe disease requiring ICU admission and prolonged ventilation, although fatal outcome is overall rare.
16 US Sta Art Fi 10/02/20 COVID-19 Trends Among School-Aged Children — United States, March 1–September 19, 2020. MMWR Morb Mortal Wkly Rep
Underlying conditions were more common among school-aged children with severe outcomes related to COVID-19: among school-aged children who were hospitalized, admitted to an intensive care unit (ICU), or who died, 23%, 38%, and 33%, respectively, had at least one underlying condition.
17 US Sta Art Fi 01/22/21 COVID-19 Trends Among Persons Aged 0–24 Years — United States, March 1–December 12, 2020. MMWR Morb Mortal Wkly Rep
COVID-19 cases in children, adolescents, and young adults have increased since summer 2020, with weekly incidence higher in each successively increasing age group.
18 Iceland Sta Art Fi 06/11/20 Spread of SARS-CoV-2 in the Icelandic Population. N Engl J Med
In a population-based study in Iceland, children under 10 years of age and females had a lower incidence of SARS-CoV-2 infection than adolescents or adults and males. The proportion of infected persons identified through population screening did not change substantially during the screening period, which was consistent with a beneficial effect of containment efforts.
19 Met Art Fi 12/01/20 Household Transmission of SARS-CoV-2: A Systematic Review and Meta-analysis. JAMA Netw Open
[G]iven that individuals with suspected or confirmed infections are being referred to isolate at home, households will continue to be a significant venue for transmission of SARS-CoV-2.
20 China Sta Art Fi 06/26/20 Changes in contact patterns shape the dynamics of the COVID-19 outbreak in China. Science
[C]hildren 0 to 14 years of age are less susceptible to severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection than adults 15 to 64 years of age.
21 Met Art Fi 02/01/20 Susceptibility to SARS-CoV-2 Infection Among Children and Adolescents Compared With Adults: A Systematic Review and Meta-analysis. JAMA Pediatr.
In this meta-analysis, there is preliminary evidence that children and adolescents have lower susceptibility to SARS-CoV-2, with an odds ratio of 0.56 for being an infected contact compared with adults. There is weak evidence that children and adolescents play a lesser role than adults in transmission of SARS-CoV-2 at a population level.
22 Agg Rev 10/29/20 On the Effect of Age on the Transmission of SARS-CoV-2 in Households, Schools, and the Community. J Infect Dis
There is some evidence that given limited control measures, SARS-CoV-2 may spread robustly in secondary/high schools, and to a lesser degree in primary schools, with class size possibly affecting that spread. There is also evidence of more limited spread in schools when some mitigation measures are implemented.
23 Israel Epi Household Art Fi 08/2020 The Role of Children in the Dynamics of Intra Family Coronavirus 2019 Spread in Densely Populated Area. Pediatr Infect Dis J.
Our investigation demonstrated significantly lower rates of COVID-19 positivity in children compared with adults residing in the same household.
24 Italy Sta Art Fi 06/30/20 Suppression of a SARS-CoV-2 outbreak in the Italian municipality of Vo’. Nature
The experience of Vo’ shows that, despite the silent and widespread transmission of SARS-CoV-2, transmission can be controlled and represents a model for the systematic suppression of viral outbreaks under similar epidemiological and demographic conditions.
25 Met Art Fi 12/06/20 A meta-analysis on the role of children in SARS-CoV-2 in household transmission clusters. Clin Infect Dis.
Children are Infrequently Identified as the Index Case of Household SARS-CoV-2 Clusters
26 US, NY Sta Let Fi 05/20/20 Nasal Gene Expression of Angiotensin-Converting Enzyme 2 in Children and Adults. JAMA.
[C]ompared with younger children, ACE2 gene expression was significantly higher in older children.
27 Nar Let Fi 05/06/20 The immune system of children: the key to understanding SARS-CoV-2 susceptibility?. Lancet Child Adolesc Health.
Children are more vulnerable to other infections; thus, the important question arises—why are children less susceptible to COVID-19 disease compared with adults? So far, there is no evidence of a lower degree of expression or function of the SARS-CoV-2 receptor (namely ACE2) in children. Thus, studying the innate immune system of children might be the key
28 US, NY Sta Let Fi 11/05/20 Distinct antibody responses to SARS-CoV-2 in children and adults across the COVID-19 clinical spectrum. Nat Immunol
The clinical manifestations of SARS-CoV-2 infection in children are distinct from adults. Children with COVID-19 rarely exhibit severe respiratory symptoms and often remain asymptomatic
29 Israel Sta Art Fi 02/11/21 The role of children in the spread of COVID-19: Using household data from Bnei Brak, Israel, to estimate the relative susceptibility and infectivity of children. Preprint. MedRxiv
[T]he fraction of children among the confirmed cases has been found to be low in many countries can be accounted for by two (nonexclusive) hypotheses: (1) Children display milder symptoms than adults when infected, so are less likely to be tested in a typical testing policy triggered by symptoms, (2) Children are less susceptible to infection than adults. Our analysis of the data obtained in this study lends support to <em>both</em> hypotheses, and indicates that both have a role in explaining the observed epidemiological patterns.
30 South Korea Sta Art Fi 10/2020 Contact Tracing during Coronavirus Disease Outbreak, South Korea, 2020. Emerg Infect Dis
Of 10,592 household contacts, 11.8% had COVID-19. Of 48,481 nonhousehold contacts, 1.9% had COVID-19.
31 China Sta Art Pr 07/24/20 Infectivity, susceptibility, and risk factors associated with SARS-CoV-2 transmission under intensive contact tracing in Hunan, China. Preprint. MedRxiv
Our findings support the hypothesis that children can effectively transmit SARS-CoV-2 and highlight how pre-symptomatic and asymptomatic transmission can hinder control efforts.
32 UK Sta Art Fi 08/24/20 SARS-CoV-2 infection and transmission in educational settings: a prospective, cross-sectional analysis of infection clusters and outbreaks in England. Lancet Infect Dis
Overall, SARS-CoV-2 infections and outbreaks were uncommon across all educational settings. Staff members had an increased risk of SARS-CoV-2 infections compared to students in any educational setting, and the majority of cases linked to outbreaks were in staff.
33 Europe Sta Art Pr 11/13/20 Age differential analysis of COVID-19 second wave in Europe reveals highest incidence among young adults. Preprint. MedRxiv
[W]e analyze data of incidence by age groups in 25 European countries, revealing that the highest incidence of the current second wave is observed for the group comprising young adults (aged 18-29 years old) in all but 3 of the countries analyzed.
34 Italy Mod Art Pr 12/18/20 No evidence of association between schools and SARS-CoV-2 second wave in Italy. Preprint. MedRxiv
[S]chool closures in two regions where they were implemented before other measures did not affect the rate of Rt decline. In schools, despite the high frequency of tests per week, secondary infections were <1%, and clusters in a representative November week infrequent. Thus, our prospective analysis does not support a role for school reopening as a driver of the second wave of SARS-CoV-2 epidemics in Ital
35 US Sta Art Fi 01/04/21 The Effects of School Reopenings on COVID-19 Hospitalizations. Technical Report from the National Center for Research on Education Access and Choice (REACH).
The study is the first to examine how reopening schools in-person has affected COVID-19 hospitalizations. We found no evidence that reopening schools in-person or in a hybrid form increased COVID hospitalizations in the 75 percent of counties that had low COVID hospitalization rates during the summer, prior to reopening schools. Our results suggest that it seems safe to reopen schools when there are no more than 36 to 44 total new COVID hospitalizations per 100,000 people per week.
36 Israel Epi School Art Fi 07/23/20 A large COVID-19 outbreak in a high school 10 days after schools’ reopening, Israel, May 2020. Euro Surveill
The high school outbreak in Jerusalem displayed mass COVID-19 transmission upon school reopening. The circumstances promoting infection spread involved return of teenage students to their regular classes after a 2-month closure (on 18 May) and an extreme heatwave (on 19 May) with temperatures rising to 40 °C and above [6] that involved exemption from facemasks and continuous air-conditioning.
37 Germany Sta Art Fi 09/2020 Surveillance of COVID-19 school outbreaks, Germany, March to August 2020. Euro SurveillSurveillance of COVID-19 school outbreaks, Germany, March to August 2020
Only few and mostly small COVID-19 school outbreaks had been reported in Germany overall, suggesting that the containment measures are sufficient to reduce spillover into the community.
38 US, MI/WA Mod Art Fi 2/2021 To What Extent Does In-Person Schooling Contribute to the Spread of COVID-19? Evidence from Michigan and Washington. Report from the Center for Education Data & Research (CEDR), National Center for Analysis of Longitudinal Data in Education Research (CALDER), and Education Policy Innovation Collaborative (EPIC).
Using a variety of regression modeling strategies , we find that simple correlations show in-person modalities are correlated with increased COVID cases, but accounting for both pre-existing cases and a richer set of covariates brings estimates close to zero on average.
39 US, NC Epi School Art Pr 1/2021 Incidence and Secondary Transmission of SARS-CoV-2 Infections in Schools. Pediatrics.
In the first 9 weeks of in-person instruction in North Carolina schools, we found extremely limited within-school secondary transmission of SARS-CoV-2, determined by contact tracing
40 Singapore Epi School/ECOC Art Fi 06/25/20 Novel coronavirus 2019 transmission risk in educational settings. Clin Infect Dis.
The data suggest that children are not the primary drivers of SARS-CoV-2 transmission in schools and could help inform exit strategies for lifting of lockdowns.
41 Germany Epi School/ECOC Art Fi 09/10/20 Transmission of SARS-CoV-2 in children aged 0 to 19 years in childcare facilities and schools after their reopening in May 2020, Baden-Württemberg, Germany. Euro Surveill.
Child-to-child transmission in schools/childcare facilities appeared very uncommon. We anticipate that, with face mask use and frequent ventilation of rooms, transmission rates in schools/childcare facilities would remain low in the next term, even if classes’ group sizes were increased.
42 US, WI Sta Art Fi 01/29/21 COVID-19 Cases and Transmission in 17 K–12 Schools — Wood County, Wisconsin, August 31–November 29, 2020. MMWR Morb Mortal Wkly Rep.
Among 17 rural Wisconsin schools, reported student mask-wearing was high, and the COVID-19 incidence among students and staff members was lower than in the county overall (3,453 versus 5,466 per 100,000). Among 191 cases identified in students and staff members, only seven (3.7%) cases, all among students, were linked to in-school spread.
43 US, MS Sta Art Fi 12/18/21 Factors Associated with Positive SARS-CoV-2 Test Results in Outpatient Health Facilities and Emergency Departments Among Children and Adolescents Aged &lt;18 Years — Mississippi, September–November 2020. MMWR Morb Mortal Wkly Rep.
Among children and adolescents aged &lt;18 years in Mississippi, close contact with persons with COVID-19 and gatherings with persons outside the household and lack of consistent mask use in school were associated with SARS-CoV-2 infection, whereas attending school or child care was not associated with receiving positive SARS-CoV-2 test results.
44 Australia Sta Art Fi 10/21/20 COVID-19 in schools and early childhood education and care services – the Term 3 experience in NSW. Report from National Centre for Immunisation Research and Surveillance (NCIRS). 2020; Published 2020 October.
Three larger outbreaks occurred, all in high school settings. Factors that may have contributed to these outbreaks include attending school while symptomatic, a non–school-related overnight retreat and participation in a music group. All outbreaks were rapidly contained with NSW public health response strategy. The likelihood of cases in educational settings is related to the level of community transmission of SARS-CoV-2. This is consistent with findings from Victoria, Australia4 and from international studies.
45 Finland Epi School Art Ot 07/30/20 Transmission of SARS-CoV-2 following exposure in school settings: experience from two Helsinki area exposure incidents. Preprint. MedRxiv
When the index was a child, no school transmission was identified, while the occurrence of an adult case led to a 16% AR. Further cases were evidenced in 3 families, but other transmission chains were plausible. It is likely that transmission from children to adults is limited.
46 Ireland Sta Art Fi 05/28/20 No evidence of secondary transmission of COVID-19 from children attending school in Ireland, 2020. Euro Surveill
[E]xamination of all Irish paediatric cases of COVID-19 attending school during the pre-symptomatic and symptomatic periods of infection (n = 3) identified no cases of onward transmission to other children or adults within the school and a variety of other settings. These included music lessons (woodwind instruments) and choir practice, both of which are high-risk activities for transmission. Furthermore, no onward transmission from the three identified adult cases to children was identified.
47 Australia Sta Art Fi 08/03/20 Transmission of SARS-CoV-2 in Australian educational settings: a prospective cohort study. Lancet Child Adolesc Health.
SARS-CoV-2 transmission rates were low in NSW educational settings during the first COVID-19 epidemic wave, consistent with mild infrequent disease in the 1·8 million child population. With effective case-contact testing and epidemic management strategies and associated small numbers of attendances while infected, children and teachers did not contribute significantly to COVID-19 transmission via attendance in educational settings.
48 Italy Epi School/ECOC Art Fi 12/2020 Secondary transmission of COVID-19 in preschool and school settings in northern Italy after their reopening in September 2020: a population-based study. Euro Surveill
The overall secondary case attack rate was 3.2%, reaching 6.6% in middle and high schools. More timely isolation and testing of classmates could be effective in reducing virus transmission in this setting.
49 Spain Nar Let Fi 10/05/20 COVID-19: Social Irresponsibility of Teenagers Towards the Second Wave in Spain. J Epidemiol
This situation is beginning to occur also in other countries, such as Japan. A recent study shows that the majority of young adults who start outbreaks are asymptomatic, when they are not yet aware that they can infect other people, and they do so mainly in situations where they breathe hard and there is little social distance, such as singing in karaoke bars, screaming in pubs, or working out in gyms
50 Nar Edi Fi 01/26/21 Data and Policy to Guide Opening Schools Safely to Limit the Spread of SARS-CoV-2 Infection. JAMA.
[T]he preponderance of available evidence from the fall school semester has been reassuring insofar as the type of rapid spread that was frequently observed in congregate living facilities or high-density worksites has not been reported in education settings in schools.
51 Nar Art Fi 12/11/20 Summary of Guidance for Public Health Strategies to Address High Levels of Community Transmission of SARS-CoV-2 and Related Deaths, December 2020. MMWR Morb Mortal Wkly Rep.
No single strategy can control the pandemic; rather, a multipronged approach using all available evidence-based strategies at the individual and community levels can break transmission chains and address high levels of community transmission; reduce related illnesses, long-term sequelae, and deaths; and mitigate the pandemic’s economic impact.
52 Norway Epi School Art Fi 01/2021 Minimal transmission of SARS-CoV-2 from paediatric COVID-19 cases in primary schools, Norway, August to November 2020
This prospective study shows that transmission of SARS-CoV-2 from children under 14 years of age was minimal in primary schools in Oslo and Viken, the two Norwegian counties with the highest COVID-19 incidence and in which 35% of the Norwegian population resides.
53 Switzerland Sta Art Pr 12/26/20 Surveillance of acute SARS-CoV-2 infections in school children and point-prevalence during a time of high community transmission in Switzerland. Preprint. MedRxiv
In a setting of high incidence of SARS-CoV-2 infections, unrecognized virus spread within schools was very low. Schools appear to be safe with the protective measures in place (e.g., clearly symptomatic children have to stay at home, prompt contact tracing with individual and class-level quarantine, and structured infection prevention measures in school).
54 US, IL Sta Art Fi 12/30/21 Data-Driven Reopening of Urban Public Education Through Chicago’s Tracking of COVID-19 School Transmission. J Public Health Manag Pract
By combining local data from a large urban private school system with national and international data on maintaining in-person learning during COVID-19 surges, Chicago believes in-person public education poses a low risk of transmission when the operational burden imposed by the second wave has subsided.
55 South Korea Epi Fitness Center Art Fi 05/15/20 Cluster of Coronavirus Disease Associated with Fitness Dance Classes, South Korea. Emerg Infect Dis. 2020
During 24 days in Cheonan, South Korea, 112 persons were infected with severe acute respiratory syndrome coronavirus 2 associated with fitness dance classes at 12 sports facilities. Intense physical exercise in densely populated sports facilities could increase risk for infection.
56 South Korea Epi Fitness Center Art Fi 08/10/20 Epidemiological Characteristics of COVID-19 Outbreak at Fitness Centers in Cheonan, Korea. J Korean Med Sci
Zumba is an exercise fitness program which combines aerobic exercise with music, and Oriental and Latin dance moves.5 In the fitness centers where the Zumba classes were held, a large number of students had taken classes in a relatively crowded space, although ventilation systems were working properly. … [T]he droplets produced by exhalation or cough of a patient during the exercise have higher chance of reaching the nose, mouth or eye of other class participants directly, as well as remaining on the surface of the exercise equipment and later transmitted by contact.
57 US, FL Epi School Gym Art Fi 10/16/20 An Outbreak of COVID-19 Associated with a Recreational Hockey Game — Florida, June 2020. MMWR Morb Mortal Wkly Rep
The study was unable to determine exactly where exposure occurred, but hypothesizes it was at the evening hockey game, due to the heavy breathing that occurs, the lack of masks covering the mouth and nose, the transition from ice to bench where players continue heavy breathing or in the locker rooms and lack of other common exposures or time spent together.
58 US, FL Epi School Gym Art Fi 01/26/21 SARS-CoV-2 Transmission Associated with High School Wrestling Tournaments — Florida, December 2020–January 2021. MMWR Morb Mortal Wkly Rep
An outbreak arising from a Florida high school wrestling tournament in December 2020 had an attack rate of at least 30% (38 of 126 tournament attendees who were tested) and a secondary attack rate of at least 9% (41 of 441 close contacts of the 38 COVID-19 patients)
59 US, WA Epi Choir Room Art Fi 05/15/20 High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice — Skagit County, Washington, March 2020. MMWR Morb Mortal Wkly Rep.
Transmission was likely facilitated by close proximity (within 6 feet) during practice and augmented by the act of singing.
60 France Epi Choir Room Art Fi 12/23/20 High Rate of SARS-CoV-2 Transmission Due to Choir Practice in France at the Beginning of the COVID-19 Pandemic. J Voice.
The characteristics of the viral transmission via close human contacts was probably enhanced by the act of singing, at a phase of intense circulation of SARS-CoV-2 in the population at this period. We report in our study the role of asymptomatic infection carriers initiating a silent chain of transmission of the coronavirus, leading to a cluster under the circumstances of the rehearsal. This study confirms that the transmission of the virus from asymptomatic cases is very efficient.
61 Agg Art Fi 08/27/20 Droplets and Aerosols Generated by Singing and the Risk of Coronavirus Disease 2019 for Choirs. Clin Infect Dis. 2020;ciaa1241. Published online ahead of print 2020 Sep 18. doi:10.1093/cid/ciaa
While social distancing is effective in normal social interactions, singing can produce a substantially larger number of respiratory droplets and aerosols than speaking, as it is louder and sustained for longer durations

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