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COVID-19: What Is and Is Not Known

COVID-19 is the name for the clinical disease caused by infection with SARS-CoV-2, a virus first recognized in China in late 2019. COVID-19 is a highly infectious disease that grew rapidly into a major global pandemic resulting in hundreds of thousands of deaths worldwide. This chapter begins with a brief preliminary history of COVID-19. It then reviews current knowledge about the prevalence, distribution, and transmission of COVID-19; its impact on children, adults, and marginalized communities; and preliminary mitigation efforts. The chapter ends with the committee’s conclusions on these topics. The committee relied on this science to guide our conclusions and recommendations related to the reopening of K–12 schools later in this report.

PRELIMINARY HISTORY OF COVID-19

The COVID-19 outbreak was first recognized in Wuhan, China, in December 2019. By late January, the World Health Organization (WHO) had declared a public health emergency of international concern on the advice of the agency’s emergency committee, marking a global effort to prevent, detect, and respond to the spread of the virus. In the United States, community transmission was first recognized in late February, but likely had been occurring for some time before then. By mid-March, thousands of cases had been identified across the country.

In response to the intense transmission of the virus in the United States, governors took bold steps to curtail the disease, including making unprecedented decisions to close large congregate spaces, such as churches

and malls. K–12 schools were among the first institutions to close their buildings, changing access to and modalities of the delivery of education for children. For most school systems, these closures were extended for the rest of the school year and into the summer. As those jurisdictions look ahead to the new school year, they face complex questions about whether and how to reincorporate in-person learning.

As the disease continues to unfold, the committee is reminded of how much has been learned in the past months, yet how much remains to be known to better understand how to construct, operate, and gather in environments in a way that is safe and minimizes the risks to children and their families.

PREVALENCE AND DISTRIBUTION

Globally, as of July 10, 2020, there were more than 12.9 million cases of confirmed COVID-19, with 570,250 deaths attributed to the disease. According to data collated by The Johns Hopkins University, the United States accounts for 135,270 of these deaths as of July 10, 2020.

Of the 3.3 million reported cases in the United States as of July 10, 2020, the Centers for Disease Control and Prevention (CDC) estimates that roughly 5 percent of symptomatic cases in the United States are found among children. However, cases among children are undercounted because of the low volume of COVID-19 testing nationally among the pediatric population, with older age groups and those presenting with severe respiratory symptoms having been the testing priority.

According to the CDC, the vast majority of positive cases are in people aged 18–64. While people under the age of 65 represent a significant number of positive cases, those aged 60–85 who test positive for the virus are at highest risk for severe illness and death. Black, Hispanic¹/LatinX, and Indigenous populations account for 55 percent of all COVID-19 cases—a disproportionate share given that they represent about 33 percent of the U.S. population.

Not all communities in the United States have been affected by COVID-19 in the same way. States in the Northeast, particularly New York and New Jersey, were hit early and hard, but had begun to turn the corner by mid-April and as of this writing were experiencing relatively low levels of transmission. In contrast, other areas not heavily affected in the first few months of the outbreak, particularly in the South and West, have begun to struggle with increased transmission. These geographic and temporal patterns will likely continue to change as flareups and efforts to regain control

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¹ The committee uses the term LatinX throughout this report, unless the research cited specifically uses a different term.

change the epidemiological picture. School systems will need to take local epidemiology into account when making decisions about whether and how to open and close.

TRANSMISSION

SARS-CoV-2 is transmitted primarily by respiratory droplets from close contact with infected persons, and by surfaces that have been contaminated by infected persons and then touched by previously uninfected persons who then touch their mouth, nose, or eyes without first properly washing their hands. The average number of secondary cases per infectious case ranges from 2.5 to well over 3.0, making this virus considerably more infectious than influenza (Inglesby, 2020). Current evidence suggests that, given how the virus is spread, prolonged close contact in indoor environments is particularly high risk (Centers for Disease Control and Prevention [CDC], 2020b). The median incubation period, regardless of age, is estimated to be about 5 days, with a range of 2–14 days (Rasmussen and Thompson, 2020).

Scientific knowledge about the impact of the virus on adults and children is evolving. Early studies relying on symptom-based surveillance suggested that children were at lower risk than adults for contracting the disease. According to data through June 18, 2020, just 4.9 percent of confirmed cases in the United States had been diagnosed in children aged 0–17 (CDC, 2020a), a statistic supported by studies showing that the proportion of exposed household members is lower in children than in adults (Jing et al., 2020; Li et al., 2020; Zhang et al., 2020). However, one recent study using contact-based surveillance found that children had been infected at rates similar to those for adults, but that they were either asymptomatic or had symptoms too mild to be detected (Bi et al., 2020). Additional seroprevalence (the level of a pathogen in a population, as measured in blood serum) studies are still needed to understand the prevalence of the disease in children in the United States (Ludvigsson, 2020; Rasmussen and Thompson, 2020).

Although it is clear that onward transmission from infected children is possible, it is not yet clear whether children are less likely to transmit than are adults, on average. Several studies have shown that viral loads in symptomatic children are similar to those of adults. However, studies of viral load do not always correlate well with infectiousness, and little information is available on the infectiousness of asymptomatic or subclinically infected children. These uncertainties make it difficult to evaluate the epidemiological risks of reopening schools. If children are efficient transmitters, evidence from influenza suggests that physically reopening schools (without mitigation measures) could contribute substantially to community spread.

However, if children are not efficient transmitters or if such mitigation measures as use of face coverings are very effective, physically reopening will be safer. See Box 2-1 for a summary of key findings related to transmission.

IMPACT ON CHILDREN

Compared with adults, children who contract COVID-19 are more likely to experience asymptomatic infection or mild upper respiratory symptoms. It is estimated that more than 90 percent of children who test positive for COVID-19 will have mild symptoms, and only a small percentage of symptomatic children (estimates range from 1 to 5 percent) will have severe or critical symptoms (Prather, Wang, and Schooley). Notably, children relative to adults are less likely to develop a fever or cough—two symptoms commonly used to identify cases through symptom-based screening (Lu et al., 2020; U.S. Department of Health and Human Services, 2020). To date, identified risk factors for severe disease among children include age <1 year (and thus not school age) or existing comorbidities. Accordingly, the role of chronic medical conditions in disease severity remains a major concern. A retrospective study of 177 children found that 63 percent of those hospitalized with COVID-19 had underlying conditions, compared with 32 percent of nonhospitalized patients, and 78 percent of critically ill chil-

dren had underlying conditions, compared with 57 percent of hospitalized, non–critically ill patients (DeBiasi et al., 2020). In one study summarizing early data from the United States, 77 percent of children hospitalized with COVID-19 had at least one underlying health condition (U.S. Department of Health and Human Services, 2020). In New York City, 8 of 9 (89%) children with severe COVID-19 infection had an underlying condition, compared with 61 percent of children with nonsevere illness (Zachariah et al., 2020).

Recent case reports suggest that a new hyperimmune response known as multisystem inflammatory syndrome (MIS-C) may be a rare sequela of SARS-CoV-2 infection. MIS-C associated with COVID-19 infection has shown moderate to severe impacts on children’s vital organs and gastrointestinal and circulatory systems, and according to some evidence has resulted in symptoms similar to those of Kawasaki syndrome, which is characterized by acute inflammation of the blood vessels in children. In Italy, for example, 10 patients with Kawasaki-like disease were identified over the course of 2 months, compared with 19 patients in the preceding 5-year period (Verdoni et al., 2020). In addition, children who have been hospitalized for COVID-19 sometimes require treatment for inflammation of the heart, lungs, kidney, gastrointestinal tract, brain, and eyes. Although the epidemiology of MIS-C has not yet been well characterized, experts suggest that it is rare for COVID-19-positive children to develop the syndrome and that most children diagnosed with MIS-C recover.

There are currently two therapeutics that have received emergency use authorization for treating COVID-19, and researchers around the world are working to develop medicines and vaccines to treat and reduce the virulence of the virus. In the United States, there are more than 457 experimental drugs under development and roughly 144 active clinical trials, according to the U.S. Food and Drug Administration (FDA) (U.S. Food and Drug Administration, 2020). It should be noted that no clinical trials have specifically targeted the treatment of children, and many unanswered questions remain about the best therapeutics for children, in part because of the limited number of cases of symptomatic disease in this population (Castagnoli et al., 2020; Kelvin and Halperin, 2020; Rasmussen and Thompson, 2020).

Population-based data tell only part of the story; how to apply those data to individual children is challenging. While it is clear that children with underlying disease, particularly those with progressive conditions (Bailey et al., 2020), are at increased risk of severe complications, it is not yet known how great the absolute risk of severe COVID-19 disease is for children with more common conditions (e.g., asthma) and how those risks should be counterbalanced against the risks of not attending school. Based on the limited data to date, clear guidelines on which children are at sufficiently high risk to require alternative educational modalities is

not possible. Parents need to consult with their child’s pediatrician, and accommodations need to be made for children for whom the risk of school attendance is deemed too great.

IMPACT ON ADULTS

Although children make up the majority of school populations, schools are also workplaces for many adults, and decisions around how and when to reopen schools will need to account for risks to these older and at-risk populations as well. Consideration must also be given to household members and other close contacts of children outside of the school setting, some of whom may be vulnerable to severe infection.

COVID-19 infection in adults can cause illness ranging from asymptomatic or mild upper respiratory symptoms to acute respiratory distress. Common symptoms include fever, cough, difficulty breathing, and loss of sense of smell. Severity of illness is associated with age; cumulative rates of hospitalization (as of this writing) range from 27.3 per 100,000 population in adults aged 18–29 to 136 per 100,000 in adults aged 50–64. Those at highest risk of severe illness include people 65 and older and those with underlying health conditions, including chronic lung disease, serious heart conditions, severe obesity, diabetes, chronic kidney disease requiring dialysis, and liver disease, and those who are immunocompromised (CDC, 2020e).

According to the CDC, age-adjusted hospitalization rates are highest among non-Hispanic American Indian or Alaska Native and non-Hispanic Black people, followed by Hispanic or LatinX people. Compared with the non-Hispanic white population, rates of hospitalization are approximately five times higher in the non-Hispanic American Indian or Alaska Native population, 4.5 times higher in the non-Hispanic Black population, and 4 times higher in the Hispanic or LatinX population (CDC, 2020c).

DISPRORTIONATE IMPACTS ON MARGINALIZED COMMUNITIES

Black, LatinX, Native American, immigrant, and marginalized low-income populations have been disproportionately impacted by COVID-19. The rates of exposure, positive tests, and deaths due to complications of the disease are greater among these populations compared with their white counterparts. The CDC reports that age-adjusted hospitalization rates are highest for American Indian or Alaska Native populations at 193.8 per 100,000, followed by non-Hispanic Black (171.8 per 100,000) and Hispanic/LatinX populations (150.3). Asian and white populations have the lowest age-adjusted hospitalization rates, at 44.9 and 37.8 per 100,000, respectively (CCD, 2020c). These statistics vary across the coun-

try: in New York City, over 50 percent of tests administered in some communities of color were positive at the height of the outbreak (NYC Department of Health and Mental Hygiene, 2020). These gross disparities not only result in poor clinical outcomes associated with COVID-19 but also include a host of social and financial impacts that further exacerbate the structural challenges experienced by these groups.

There are many emerging explanations as to why people of color have been impacted disproportionately by the disease. One set of explanations relates to health status, such as a higher burden of underlying health conditions and limited access to testing and treatment. However, other factors beyond health status may contribute. For example, people of color and those from other marginalized groups are more likely to be employed in lower-wage jobs that are essential to maintaining the operations and infrastructure of communities—for example, jobs related to building sanitation, food production, transportation, material moving, stock production, and municipal services—and were therefore unable to stay home during shutdowns (Rasmussen and Thompson, 2020). They also are more likely to be unable to quarantine or isolate because of family housing or fear of lost wages due to unpaid sick leave. And they are more likely to be unemployed or to work in multiple part-time jobs, limiting their access to health insurance coverage and ability to pay for medical care.

PRELIMINARY MITIGATION EFFORTS

Efforts undertaken thus far to mitigate the spread of COVID-19 include stay-at-home and shelter-in-place orders; testing and contact tracing; social distancing, hand hygiene, and use of face coverings; personal protective equipment; and temperature screenings.

Stay-at-Home and Shelter-in-Place Orders

Stay-at-home and shelter-in-place orders are emergency measures designed to break chains of transmission and limit the spread of disease by asking or requiring that people remain at home. Beginning in March 2020, schools, businesses, and leisure activities in many states were closed, with only essential businesses and services, such as grocery stores and emergency health care, remaining open. These decisions were made largely by governors at the state level. Although extremely disruptive, these measures were effective at slowing the transmission of COVID-19 to prevent health care systems from becoming overwhelmed and to give public health officials time to improve capacities to expand diagnostic testing and scale contact tracing programs.

Testing and Contact Tracing

Diagnostic testing and contact tracing, also known as case-based management, are outbreak containment strategies that focus specifically on people who are infected and those who have been exposed and are therefore at risk of becoming sick. To implement this strategy, everyone with COVID-19-like symptoms should undergo a diagnostic test and receive the results within, ideally, 24 hours. Those who test positive are asked to remain at home (or in a hospital or hotel, if care or alternative accommodations are needed) for the duration of their illness to avoid exposing others. A public health official contacts the newly diagnosed person and conducts an interview aimed at identifying everyone who was exposed to that individual for 10–15 minutes or more, dating back to 2 days before the onset of symptoms. Public health officials then notify those close contacts about their exposure and ask that they remain at home for 14 days so that should they become ill, they will not expose anyone else. Chains of transmission are thereby broken, and the virus is “boxed in” (Resolve to Save Lives, 2020). Case-based management strategies have allowed a number of countries, including New Zealand, Singapore, and South Korea, to control transmission substantially and safely reopen some community activities.

Physical Distancing, Hand Hygiene

Physical distancing (also called social distancing), hand hygiene, and use of facial coverings are individual-level interventions intended to reduce the risk of infection.

Physical distancing prevents the close contact that makes it easy for the virus to pass from one person to another. Six feet is the most commonly recommended distance in the United States, but this is a rule of thumb, not a definitively safe distance.

Similarly, handwashing reduces the risk of infection from hand-to-face behaviors or during food preparation or other opportunities for the virus to enter the eyes, nose, or mouth. Opportunities for handwashing include before eating; when coming in from outside; after using the bathroom or a facial tissue; and before spending time with others, particularly those at high risk of severe illness. Alcohol-based hand sanitizer may be used if soap and water are not readily available.

Personal Protective Equipment

For health care workers and others in high-risk roles, a higher level of personal protective equipment than that for the general population is recommended to prevent the wearer from becoming infected. The CDC

recommends that all health care personnel wear a surgical or procedural face mask at all times while in a health care facility. Personnel caring for someone with a suspected or confirmed case of COVID-19 are recommended to wear an N95 respirator, a face shield or goggles, an isolation gown, and gloves. Additional guidance on personal protective equipment in health care settings is available on the CDC website.²

Because of severe supply shortages, medical-grade personal protective equipment is not recommended for use by the general public. The fabric face coverings recommended by the CDC provide only minimal protection to the wearer; they are intended to reduce risk to others. Because one major mode of transmission is through droplets produced during speaking, singing, coughing, or sneezing, facial coverings that act as a barrier to prevent those droplets from spreading can theoretically reduce the risk of transmission. Although this mitigation strategy is not well described in the literature, there is mechanistic plausibility for it, and use of face coverings is now recommended by both the CDC and WHO (World Health Organization, 2019).

Temperature Screenings and Symptom Screenings

Temperature screenings are intended to identify people with a fever that may indicate an infection. The screenings are usually conducted with a noncontact thermometer or according to the CDC’s recommended protocol (CDC, 2020b). The effectiveness of temperature screenings as a coronavirus mitigation measure is not known. Although most adults (70%) infected with the virus have a fever at some point in their illness, the proportion is lower for children (Stokes et al., 2020; U.S. Department of Health and Human Services, 2020). In the setting of international travel, temperature screenings have been found to have a low sensitivity (Gostic et al., 2015). In school settings, the CDC recommends that screening be conducted, but it need not be limited to temperature screening; it could also include, for example, symptom screening (CDC, 2020b).

CONCLUSIONS

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² See https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control-recommendations.html.

Conclusion 2.2: Black, LatinX, and Indigenous people; low-income populations; and children and adults with chronic underlying health conditions are disproportionately impacted by COVID-19. Although all people are susceptible to the virus, regardless of race or income, underlying inequities in access to health resources, inflexible employment, and housing and economic issues make certain populations more vulnerable to transmission of and poor outcomes from the disease.

Conclusion 2.3: Mitigation strategies such as physical distancing, handwashing, use of face coverings, symptom screening, and avoiding large gatherings can reduce the risk of spread of the virus, and will be particularly important in managing how students and adults interact within indoor spaces such as schools and classrooms.

Conclusion 2.4: COVID-19 has more serious health consequences for adults who contract the virus than for children. Mitigation strategies implemented in schools are especially important for protecting school staff and limiting potential transmission of the virus to vulnerable adults in the families of students and school staff.