In March 2020, kindergarten through 12th grade (K-12) schools across the United States and around the globe abruptly halted in-person education. This immediate and collective decision was based on the premise that in-school learning would fuel the COVID-19 pandemic and that closing school buildings could help stop community spread of SARS-CoV-2.
In the years since these initial school closures, scientists, clinicians, public health experts, educators, and communities have learned much about the epidemiology of COVID-19, as well as the factors contributing to its spread and the strategies that successfully mitigate transmission. Such strategies, when applied in school settings, allow for safe, in-person learning. We are also beginning to learn the detrimental consequences of pandemic-related school closures, including worsening mental health1 among children and adolescents, increased childhood obesity,2 and overall learning loss; we likely will not know the full effects of these consequences for many years. These public policy failures have disproportionately affected children in low-income, high-poverty schools,3 thereby exacerbating longstanding disparities in education.
Future pandemics are inevitable, and when they arrive, we can hopefully avoid past pitfalls and instead transform the lessons learned from the COVID-19 pandemic into better support for children. We describe these key lessons in this article, which pertain to circumstances in which vaccination and therapeutic agents were not yet available for children.
Lesson #1: School Closures may Have Initially Been Necessary but Should Have Been Brief
Suggestion #1 (Had we Known What we Know Today): Prioritize School Reopenings
Historically, children have been major contributors to respiratory illnesses, such as influenza. As a result, short-term school closures have become a mainstay of public health measures in epidemic and pandemic conditions. In March 2020, initial school closures for the COVID-19 pandemic allowed public health specialists and scientists to learn about this new disease, recognizing the critical importance of understanding SARS-CoV-2 transmission, morbidity, and mortality in children and adults as well as the efficacy of masking and other measures to prevent transmission. Yet by summer 2020, we had evidence that health care facilities successfully prevented transmission of SARS-CoV-2 through universal masking policies4 ; by fall 2020, we had initial data on universal masking and transmission from European primary and secondary schools, American private K-12 schools, and some North Carolina-based public school districts that reopened with mitigation strategies in place. We learned that widespread, systematic, real-time data collection could drive informed public health decisions.5,6
By January 2021, data from different parts of the United States (eg, North Carolina, Wisconsin)7,8 undeniably demonstrated that schools could successfully and safely reopen. These data also demonstrated that the primary goals and decision-making surrounding reopening for schools had to center around whether within-school transmission could be prevented, and whether schools would not (and should not) be held accountable for transmission that occurred outside of their campus buildings. Moreover, data collected during the height of the δ and ο waves demonstrated that schools with universal masking could maintain low rates of within-school transmission despite high community rates, thereby reinforcing that the important metric for success in schools was within-school transmission (Fig 1).9–11
Lesson #2: Masking is a Successful Mitigation Strategy to Prevent Within-School Transmission
Suggestion #2 (Had we Known What we Know Today): Use Masking as a Bridge to Vaccination and to Keep Schools Open Safely
Numerous studies conducted throughout the pandemic demonstrated that within-school transmission is minimal with universal masking. Compared with schools without universal masking, those who did had substantially lower within-school transmission (proportion infected/close contacts). In the setting of universal masking, transmission occurred most frequently at mealtime, among children with special needs, and during athletic activities—all situations in which adherence to masking is more difficult. Based on data from North Carolina, Georgia, and Florida, participation in indoor sports (eg, wrestling, basketball) accounted for a substantial amount of within-school transmission among high school students and staff.12–14 Ironically, many school districts that were not open to in-person instruction continued to allow athletic practices and competitions; such decisions suggest that by late 2020, school closures had less to do with child safety and scientific data than other factors.
Lesson #3: Children Can and Will Mask Appropriately
Suggestion #3 (Had we Known What we Know Today): Systematically Report Data in Partnership With Other Schools. In Schools With High Within-School Transmission, Implement Masking Monitoring as Shown in ABC Science Collaborative publications. Use Multilayer Cloth Masks Until Surgical Masks are Widely Available, and Have Approved Respirators (eg, N95 masks) on Hand for Those who are at High Risk (eg, immunocompromised) as well as Others who Want and Will Use Respirators Consistently
Early in the pandemic, masking was proposed as a key mitigation strategy, yet many questioned whether children would consistently and appropriately mask. In numerous community and school board meetings, we heard that elementary school children would not mask because they were “too young,” that middle school children would not mask because they were “too immature,” and that high school students would not mask because they were “too obstinate.” Nonetheless, our data demonstrated that proper masking adherence was near 90% in the school setting across all school ages.15
Notably, for the first 1.5 years of the pandemic, masking often referred to well-fitting cloth face coverings. Therefore, much of the available data evaluate this masking modality, although newer, more comfortable, and well-fitted options for pediatric surgical masks and N95s have become available. Such carefully designed and regulated masks are reasonable options in the setting of more transmissible variants and when masking is optional.
Lesson #4: Hybrid Education is not Supported by Data When Other Mitigation Strategies are in Place
Suggestion #4 (Had we Known What we Know Today): Prioritize Full, In-Person Education With Universal Masking in Place Rather Than Delaying Reopening or Attempting Hybrid Education
Hybrid education took multiple forms across the country; some children attended in-person education every other day, whereas others attended in-person education in 1- or 2-week blocks. The primary goal of this staggered in-person time was to reduce the number of school children in a building or classroom at the same time and allowing at least 6 feet of distance between students in hopes of reducing the spread of SARS-CoV-2. Yet, data from 3 studies in North Carolina indicate that within-school transmission (defined as the proportion infected/close contacts) remained at or below 1% when universal masking was in place, despite transitioning from hybrid education to full, in-person education.7,10,16 Other data from Utah, Missouri, and Massachusetts demonstrated that 3 feet of distance among elementary school students was sufficient to limit COVID-19 spread with universal masking in place, thereby suggesting that hybrid education was no “safer” than full-in person education and only denied students access to higher quality education.17–19
Furthermore, it is not clear how much distance substantially reduces transmission of SARS-CoV-2 in the classroom setting, particularly with evolving variants. And finally, even if an ideal distance is derived, enforcing a target distance is extremely challenging across a school day filled with various activities including bus transportation, mixing of large numbers of older students in hallways, movement within and across classrooms, and so on. Early education programs could be incorporated into these recommendations provided they are also willing and able to implement mitigation strategies, including masking; however, far fewer available data exist for this age group.
Lesson #5: Existing Evidence Does not Support Exclusion From School After COVID-19 Exposure as Helping to Prevent the Spread of SARS-CoV-2 Within School Buildings
Suggestion #5 (Had we Known What we Know Today): Prioritize In-Person Education; Exposed Persons Should be Allowed to Stay in School With Strict Adherence to Masking After Exposure. Under Circumstances Where Masking Adherence is not Possible, or Additional Reassurances are Needed, Serial, Rapid Antigen Testing can be Used to Support In-Person Education of Those Exposed
Throughout the first 1.5 years of the pandemic, studies consistently demonstrated that within-school transmission through the α, δ, and early ο variants was approximately 1% to 3% in the universal masking environment, suggesting that >90% of students and staff exposed to SARS-CoV-2 were required to stay home, despite never actually demonstrating infection.7,10,16 Moreover, when these exposed students and staff were eventually allowed to stay in school, provided they wore a mask for up to 10 days after exposure, they were highly unlikely to infect other people within school buildings.11
Lesson #6: Although Modification to the Indoor Environment to Improve Ventilation is Believed to be Important, This Strategy has Limited Evidence in the School Setting to Reduce or Limit Within-School Transmission
Suggestion #6 (Had we Known What we Know Today): Focus Ventilation Measures Where Mask Adherence is not Feasible. Eat Outdoors and Spend Money on Ventilation Upgrades in Classrooms for Children With Special Needs who are Unable to Consistently Mask, or Mask at all
In the setting of strict masking adherence, school districts making little to no changes to indoor ventilation were successful in preventing transmission of SARS-CoV-2 among students and staff.7,10,16 In these settings, outside dining and concentrating any ventilation upgrades in classrooms where children have more difficulty adhering to masking (eg, children with special needs) has often been helpful.
Previous survey data from schools demonstrated that the incidence of COVID-19 was 39% lower among schools implementing 1 or more strategies to improve classroom ventilation compared with schools that did not implement ventilation changes. Among schools that implemented ventilation changes to dilute airborne particles or to dilute and filter airborne particles, the incidence of COVID-19 was 35% and 48% lower, respectively, compared with the incidence among schools not implementing ventilation changes.12 Reports have also noted substantial spread of SARS-CoV-2 in classrooms where school leaders have invested in ventilation upgrades.20
Lesson #7: School-Based Asymptomatic Screening Testing Should not be Considered an Effective Mitigation Strategy
Suggestion #7 (Had we Known What we Know Today): Provide Testing for Symptomatic School Attendees, Leverage Testing to Facilitate School Attendance and School Activities, but do not Implement Widespread Screening Tests
In 2021, many experts and government and public health leaders advocated for mass screening testing as a mitigation strategy for K-12 schools. In part, this push for mass screening was encouraged by modeling studies that suggested that universal screening testing could virtually eliminate viral transmission.21,22 Nevertheless, real-life implementation of screening testing in K-12 schools suggested that when testing was voluntary, uptake was limited (<20%) and screening rarely identified positive asymptomatic persons, especially when universal masking was in place.23 Moreover, implementation of screening testing required substantial monetary, personnel, and time resources that are often not equally available across low- and high-poverty schools.
Systematic screening or surveillance testing can be used to quantify infection in the K-12 population, which can help facilitate decisions about implementation of mitigation strategies24 or understand the effectiveness of implementation strategies. Additionally, availability of school-based diagnostic testing has been shown to facilitate school attendance of those who may have been exposed to SARS-CoV-2 or to limit the need for school exclusion after exposure as part of a test-to-stay program.11,25,26
Lesson #8: Although the Development of Vaccines in Adults was a Resounding Success, the Development of Vaccines in Children was Unnecessarily Delayed
Suggestion #8 (Had we Known What we Know Today): Enrollment of Adolescents Should be Embedded in Adult Vaccine Trials; and Parallel (Rather Than Sequential) Enrollment is an Imperative Component of Pediatric Trial Design
We had evidence that vaccines worked by October 2020, and most likely much earlier if taking into consideration routine interim analyses that often occur in pivotal trials. Although enrollment of children 12–15 years of age started in December 2020, vaccines were not available to all Americans until 2022. The failure to enroll children in parallel (rather than sequentially) needlessly prolonged the pandemic and resulted in the unnecessary deaths of children and adults worldwide. The timing of the start of adolescent enrollment (≥12 years) can be based on a benefit-risk analysis but should occur either at study start or after an interim analysis of vaccine safety during the first pivotal trial. Younger children should be enrolled on completion of the first pivotal trial and at the same time (in parallel) across age groups: specifically, children ages 2–6, 6–11, and 12–17 years can be enrolled in a trial at the same time. Interim analyses in these trials can mitigate the risk both to the children (of doses that are too high) and financial risk to the companies (enrolling large numbers of children at a dosage that is suboptimal). At the very latest, we should have had vaccines available to children of all ages by late spring 2021. Importantly, vaccine availability to all children, as well as adequate uptake and equitable, international distribution, must happen conjointly.
These lessons learned suggest that in the event of a future pandemic, in which the transmission and mortality among children are similar to what we have seen in the COVID-19 pandemic, we can and must maximize in-person education without increasing viral spread. Early, systematic data collection and sharing, such as what was done in the ABC Science Collaborative, can help accelerate knowledge, but will require ready-made systems and relationships between school districts and health entities.
The authors thank the ABC Science Collaborative National Investigators as well as all of the school districts contributing to ABC efforts. Erin Campbell, MS, provided editorial review and submission of this manuscript but did not receive compensation for her contributions, apart from her employment at the institution where this study was conducted.
FUNDING: Research reported in this publication was supported by the Office of the Director of the National Institutes of Health under award number U24MD016258; the Office of the Director of the National Institutes of Health under award number OT2HD107559; the National Center for Advancing Translational Sciences of the National Institutes of Health under award number U24TR001608; and the National Institute of Child Health and Human Development of the National Institutes of Health under contract HHSN275201000003I. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
CONFLICT OF INTEREST DISCLOSURES: Dr Zimmerman reports funding from the National Institutes of Health and US Food and Drug Administration.