OBJECTIVES

With layered mitigation strategies, there are low rates of secondary transmission of severe acute respiratory syndrome coronavirus 2; therefore, quarantine after close-contact exposure to severe acute respiratory syndrome coronavirus 2 in the kindergarten through 12th grade (K–12) setting further disrupts in-person learning with uncertain benefit. We explored the impact of eliminating quarantine for students with mask-on-mask exposures to coronavirus disease 2019 (COVID-19) on associated secondary transmission in schools.

METHODS

This observational study was conducted in a large K–12 public school district in Omaha, Nebraska (August 1, 2020, to March 15, 2021). We assessed primary and secondary COVID-19 infections in teachers and staff, frequency of quarantine for students and staff, and the impact of eliminating quarantine on secondary transmission in mask-on-mask exposure settings.

RESULTS

A total of 18 632 and 19 604 students and 2855 staff attended in-person learning in the fall and spring semesters, respectively; 1856 primary infections were among students and staff. Despite 3947 student quarantines in the fall and 1689 student quarantines in the first 10 weeks of spring semester instruction, there were only 2 cases of secondary transmission. A local policy change removed quarantine requirements for students with mask-on-mask exposure to COVID-19. Required quarantines in the spring semester reduced by 41% per primary infection compared with the fall; no student who qualified to avoid quarantine developed a secondary infection.

CONCLUSIONS

School-based COVID-19 transmission was exceptionally low in this large K–12 Nebraska school district. Elimination of student quarantine after masked exposure to COVID-19 within school was not associated with secondary transmission. Elimination of unnecessary quarantine elimination may help maximize in-person learning in the 2021–2022 school year.

What’s Known on This Subject:

Beyond coronavirus disease 2019–related school closures, required quarantines for the purpose of reducing secondary transmission in schools caused additive disruptions to in-person education. Whether quarantines add to the safety of schools in the setting of masking is unclear.

What This Study Adds:

There were 2 cases of secondary transmission in one Nebraska school district that recorded 6025 quarantined contacts. There was no detectable secondary transmission when quarantine was eliminated for coronavirus disease 2019 exposure in masked environments.

The coronavirus disease 2019 (COVID-19) pandemic caused kindergarten through 12th grade (K–12) schools to close in the United States, beginning in March 2020. Over the past year, these school closures have had a profound impact on the education and well-being of all US children, predominantly poorer children in urban public school districts.1  Recent data reveal the various repercussions school closures have had on children, including worsening food insecurity,2  elevated rates of obesity,3  increased mental health problems, and decreased access to urgent mental health care.4  Learning losses and school dropout at a young age can have lifelong detrimental implications for health and earning potential in adulthood.5  Despite these adverse impacts, the concern that within-school transmission would significantly impact community disease burden led to widespread school closures early in the pandemic. Nevertheless, a growing body of literature supports that, when mitigation measures are implemented, schools have been oases of limited COVID-19 transmission, even in areas with high rates of community transmission.68 

When schools were open, frequent quarantines substantially disrupted in-person instruction, with 5 to 20 contacts identified and quarantined for each index case.9  Even when all students were masked, those exposed to severe acute respiratory coronavirus 2 (SARS-CoV-2) at school were asked to quarantine after exposure. A pilot investigation in which COVID-19 testing was performed after masked in-school exposures revealed extremely low rates of conversion to positive testing results post exposure.9  Despite these data, quarantines continued to be recommended in the masked environment during the 2020–2021 academic year, resulting in lost learning days and the disruption of student and family life. The purpose of this study is to explore within-school SARS-CoV-2 transmission in the context of community rates, describe the impact of quarantines on lost learning days, and examine the impact of eliminating student quarantines in the masked setting on secondary transmission.

This study took place in Douglas County, Nebraska, August 1, 2020, to March 15, 2021, in a public school district with >23 000 students and 2855 staff. This school district was composed of 25 elementary schools, 6 middle schools, 4 high schools, and 1 young adult program. On August 10, 2020, all district schools opened for in-person learning for the fall semester. A hybrid model was offered for the first week; thereafter, students opted into either full-time in-person or remote education.

Mitigation strategies within all schools included distancing whenever possible in the classroom of at least 3 ft, mandated masking of students and staff, and daily symptom screening. Classrooms were indoors, and there was limited ability to open windows. No significant changes were made to ventilation systems. Staggered lunches occurred indoors, and children were distanced 6 ft apart while eating. Cleaning protocols included frequent hand sanitizing and cleaning of high-touch surfaces between classes. Outdoor recess occurred with maintenance of cohorts and masking, although masking outdoors was relaxed as the year progressed. Athletic programs conducted symptom and temperature screening for athletes; masks for all coaches, officials, workers, and spectators; and face coverings for athletes when not involved in vigorous physical activity.

We obtained publicly accessible data on community prevalence of COVID-19 cases and percentages of positive COVID-19 test results during the study period from the Douglas County Department of Health COVID-19 dashboard. District administration provided aggregate deidentified data by semester (fall semester began August 2020, spring semester began January 2021) on student and staff enrollment, identified COVID-19 cases, and frequency of quarantines. Districts provided aggregate numbers of quarantined students and staff (those quarantined after either community or school exposures). Data collection by the district spanned the entirety of the study period, except for the winter holiday (December 22, 2020, to January 3, 2021).

A COVID-19 case patient was defined as any person who tested positive for SARS-CoV-2 via either antigen or polymerase chain reaction testing. Each case triggered investigation and contact tracing by the school principal and the Douglas County Health Department, who jointly determined if the infection was acquired in the community or the school setting using predetermined criteria and identified any close contacts. A close contact was any individual who, within a 24-hour cumulative period, was within 6 ft of a COVID-19-positive individual for ≥15 minutes.

Students and staff who had symptoms consistent with COVID-19 required a negative test result before reentry; if testing was not obtained, then a minimum 10-day isolation period was followed. All confirmed cases initially required a 14-day isolation from onset of symptoms. On November 11, 2020, isolation duration was reduced to 10 days if the case patient was fever-free without medication and had symptom improvement. Similarly, close contacts of COVID-19 case patients were initially required to quarantine for 14 days from last exposure to the person with COVID-19, and no testing was mandated before return to school after this period. On September 21, 2020, an updated Directed Health Measure (DHM) issued by the Nebraska Department of Health and Human Services allowed masked students exposed to masked COVID-19-positive persons (students or staff) in school (referred to as mask-on-mask exposure) to avoid quarantine. This elimination of quarantine for mask-on-mask exposure did not apply to students who had unmasked school exposures or any community exposure, nor did this apply to K–12 staff (regardless of masked or unmasked exposure), who continued to quarantine for standard periods per health department and Centers for Disease Control and Prevention (CDC) recommendations.

For students with mask-on-mask exposure who were exempt from quarantine, daily symptom monitoring was completed; however, in the absence of symptoms, the local health measure did not require testing of these students. Testing in this setting could be completed at the discretion of parents and could include either polymerase chain reaction or antigen testing. For students and staff who had exposures that required quarantine (either within-school or community exposure), quarantine duration followed CDC recommendations and testing was not required because duration was initially not impacted by a negative test result. However, on December 2, 2020, after updated CDC recommendations, the Nebraska Department of Health and Human Services issued an updated DHM allowing quarantined staff and students to return to school on day 8 after exposure if the result of a COVID-19 test obtained at 5 to 7 days was negative; in the absence of testing, a 10-day quarantine was followed. Data on the proportion of student and staff close contacts who pursued testing were not available.

We used descriptive statistics to examine the incidence of primary (community acquired) and secondary (acquired within school) COVID-19 cases, the incidence of required quarantines, and the association between elimination of quarantine for mask-on-mask exposure and secondary transmission. No personal health information data were obtained or transmitted. The Duke University Institutional Review Board approved this study (Pro00107036).

A total of 23 682 students and 2855 staff members contributed to these data. During the study period, there was widespread transmission in Douglas County, with a range of 12 to 111 cases per 100 000 people per day, averaged over a 7-day period. As of April 8, 2021, children aged 5 to 19 years accounted for 13% of all COVID-19 cases in the county.10 

Data on primary infections and quarantines are shown in Table 1. At the start of the fall semester, 18 632 students (representing 82% of all enrolled) opted for in-person learning. Throughout the fall semester, there were 817 primary infections among students, 3947 student quarantines, and 1 case of secondary transmission involving elementary students who were unmasked at recess and had attended a sleepover together. Among 2855 staff, there were 315 primary infections, 342 staff quarantines, and 1 case of secondary transmission involving unmasked exposures in adult staff within a shared high school counseling suite. In January 2021, 19 604 students (representing 87% of enrolled) returned to in-person learning. In the first 10 weeks of the spring semester, there were 596 student primary infections, 1689 student quarantines, and no cases of secondary transmission. Among staff, there were 128 primary cases, 47 staff quarantines, and no documented cases of within-school transmission. The frequency of quarantine was reduced by 41.3% per primary infection in the spring semester when compared with the fall semester (3947 quarantines for 817 primary infections in the fall; 1689 quarantines for 596 primary infections in the spring); no cases of within-school transmission were found in exposed students who met criteria to avoid quarantine.

Through the 2020–2021 school year, a large public school district in Douglas County, Nebraska, implemented layered mitigation strategies and recorded exceptionally low rates of secondary transmission of COVID-19 (0.1%) during a time of high community prevalence. The results from this report add to the increasing evidence that public K–12 schools can operate safely, even in the setting of high community transmission rates.69  Furthermore, these results are consistent with earlier work that found that continued in-person learning after mask-on-mask exposures in a school setting does not seem to fuel secondary transmission of COVID-19 in students.8,9 

As we learned about COVID-19 transmission and effectiveness of mitigation strategies, quarantines were instituted to prevent secondary transmission; however, given the low rate of secondary transmission within schools implementing mitigation strategies, quarantines have not provided additional benefit to prevention of transmission in schools. Unfortunately, quarantines have resulted in a significant disruption of in-person instruction for teachers, students, and families. The district implemented a policy in September 2020 allowing in-person learning after close contact to COVID-19-infected persons in the mask-on-mask K–12 setting. There was a notable decrease in required quarantines, considering the number of primary infections coming into the school between the fall and spring portions of our study. In the fall, for every primary infection in a student, 4 times the number of children were quarantined, and only 2 within-school transmissions occurred. In the spring semester, the amount of students quarantined per primary infection in students was 41% lower than that in the fall semester, and there was no known secondary transmission in close contacts who qualified to avoid quarantine.

Notably, quarantine incidence included both exposures in school and in the community, but only those students with mask-on-mask exposures in K–12 environments could continue learning in person; therefore, the true reduction in school-related quarantines was likely larger than this estimate. Assuming 8 days of missed education for each student or teacher quarantine, 33 064 days of in-person education in the fall and 13 688 days in the first 10 weeks of the spring semester were lost in this school district during the study period. Our findings are consistent with data from Salt Lake City, Utah,8  as well as a pilot study in St Louis County and Springfield, Missouri,9  that support elimination of quarantine for mask-on-mask exposure. Given the increasing body of literature revealing limited secondary transmission in schools, routine quarantine of in-school close contacts who are masked is not supported. Quarantine after in-school masked exposure is of even less theoretical utility as vaccination rates rise. The substantial loss of educational days, as well as decreased access to school-based therapies, resources, and nutrition, suggests that students and families are assuming all risk of quarantine with no tangible health benefits. In the K–12 setting, when both the infected student and the exposed student are masked, routine quarantine is no longer recommended for those who are asymptomatic after exposure.11 

The findings in this report are subject to at least 3 limitations. First, testing was not required for close contacts of COVID-19 case patients under the initial quarantine guidelines or after quarantine was eliminated for mask-on-mask exposure, so asymptomatic cases of secondary transmission might have been missed. However, symptomatic children were routinely tested, and if up to 50% of infections are asymptomatic, then quarantine after mask-on-mask exposures in K–12 environments would still have minimal to no public health impact on the basis of our data as well as data from other studies.8,9  Second, data were reported on an aggregate semester level, yet the policy change that eliminated quarantine occurred in the middle of the fall semester. Consequently, estimates of quarantine reduction are imperfect; however, the September 20, 2020, DHM was the only policy change that led to reduction in student quarantine occurrence (as compared with quarantine duration). Finally, we do not have data on the degree to which each individual mitigation strategy was implemented, and we are unable to determine the magnitude of effect of any individual mitigation strategy, including masking, distancing, symptom screening, or ventilation, on the lack of quarantine elimination impact or low rates of disease transmission in this district.

With essentially all students returning to in-person learning and increased vaccination rates among staff and adolescents, our study and others suggest that student quarantines after mask-on-mask exposure do not have a detectable impact on secondary transmission but substantially decrease in-person learning time. The prompt elimination of unnecessary quarantines may facilitate recovery from the emotional and academic losses accrued by US children during the 2020–2021 school year.

We thank Millard District Schools for partnering with us to provide data for this article and for their efforts to keep children safe in school during the pandemic. We acknowledge Dr James Sutfin and Jessica Carson for their role in this collaboration. Erin Campbell, MS, provided editorial review.

FUNDING: Funded in part by the Rapid Acceleration of Diagnostics Underserved Populations (U24 MD016258; National Institutes of Health agreements 1 OT2 HD107543-01, 1 OT2 HD107544-01, 1 OT2 HD107553-01, 1 OT2 HD107555-01, 1 OT2 HD107556-01, 1 OT2 HD107557-01, 1 OT2 HD107558-01, and 1 OT2 HD107559-01); the Trial Innovation Network, which is an innovative collaboration addressing critical roadblocks in clinical research and accelerating the translation of novel interventions into life-saving therapies; and the Eunice Kennedy Shriver National Institute of Child Health and Human Development contract (HHSN275201000003I) for the Pediatric Trials Network (principal investigator, Daniel Benjamin). The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the National Institutes of Health. Funded by the National Institutes of Health (NIH).

CONFLICT OF INTEREST DISCLOSURES: Dr Boutzoukas receives salary support through the US Government Eunice Kennedy Shriver National Institute of Child Health and Human Development T32 training grant. Dr Zimmerman reports funding from the National Institutes of Health and the US Food and Drug Administration. Dr Benjamin reports consultancy for Allergan, Melinta Therapeutics, and Sun Pharma Advanced Research Company; and Drs Chick, Curtiss, and Høeg have indicated they have no potential conflicts of interest to disclose.

Drs Boutzoukas and Høeg designed the study, drafted the initial manuscript, designed the data collection instruments, collected data, conducted the initial analyses, and reviewed and revised the manuscript; Drs Chick and Curtiss reviewed and revised the manuscript; Drs Zimmerman and Benjamin conceptualized and designed the study, coordinated and supervised data collection, and critically reviewed the manuscript for important intellectual content; and all authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.

     
  • CDC

    Centers for Disease Control and Prevention

  •  
  • COVID-19

    coronavirus disease 2019

  •  
  • DHM

    Directed Health Measure

  •  
  • K–12

    kindergarten through 12th grade

  •  
  • SARS-CoV-2

    severe acute respiratory syndrome coronavirus 2

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