Three studies highlight low COVID risk of in-person school

Mask-wearing girl in school raising hand
Mask-wearing girl in school raising hand

MarianVejcik / iStock

A trio of new studies demonstrate low risk of COVID-19 infection and spread in schools, including limited in-school COVID-19 transmission in North Carolina, few cases of the coronavirus-associated multisystem inflammatory syndrome in children (MIS-C) in Swedish schools, and minimal spread of the virus from primary school students in Norway.

Infection-control policies, transparency

In the first study, published today in Pediatrics, a team led by researchers at Duke University traced contacts of North Carolina students infected with COVID-19 in 11 school districts in the first 9 weeks of in-person instruction in the fall.

In August 2020, 56 of 115 North Carolina school districts joined the ABC Science Collaborative to put in place specific public health measures to prevent COVID-19 transmission and share what they learn in the process. Superintendents reported primary and secondary cases by school and week of the quarter. The collaborative was developed by faculty at Duke University and the University of North Carolina at Chapel Hill.

Of the 56 districts participating in the collaborative, 35 offered in-person teaching for at least some of the 9 weeks, while 21 had virtual instruction only. Among the 35 with in-person classes, 17 stayed open to students for the entire quarter, and 18 did so for some of the quarter, 8 of them for at least 4 weeks. None of the schools closed because of COVID-19 transmission. Community spread in the state consisted of 1 or 2 cases per 1,000 residents for most of the quarter.

From Aug 15 to Oct 23, 11 of the 56 districts opened for in-person teaching for the first quarter of the school year. Of the more than 90,000 students and staff in the participating districts, 773 had community-acquired infections with SARS-CoV-2, the virus that causes COVID-19.

Six districts reported no secondary infections, two had one case, and three reported multiple cases. Six cases of secondary spread were in preschools, 11 in elementary schools, 6 in middle schools, 5 in high schools, and 4 in K-12 settings. Contact tracing identified another 32 cases that resulted from in-school transmission. No cases of in-school child-to-adult spread were reported.

According to the authors, the schools' public health measures successfully mitigated spread. The steps included daily screening of students and staff, compliance with mask wearing for students and adults, public reporting of COVID-19 cases, efficient contact tracing, collaboration with local health departments, regular updates for students and staff, school principal encouragement to adhere to the measures and report breaches in protocol, detailed scheduling of all parts of the school day, definitive plans for special-needs students, and opening using a hybrid model of in-person and remote learning.

The authors noted that because public schools are central to not only education but to public health and the economy, their closures have a significant impact on children and families and can be safely avoided.

"Our cohort study demonstrated that enforcing SARS-CoV-2 mitigation policies such as masking, physical distancing, and hand hygiene, resulted in minimal clusters of SARS-CoV-2 infection and low rates of secondary transmission in schools, and did not cause a larger community infection burden," the researchers concluded. "Our data indicate that schools can reopen safely if they develop and adhere to specific SARS-CoV-2 prevention policies."

Seven MIS-C cases, zero deaths in Sweden

The second study, led by Karolinska Institute researchers and published Jan 6 as a research letter in the New England Journal of Medicine, details COVID-19 cases in schools in Sweden, which kept preschools (for children 1 to 6 years) and schools (for those aged 7 to 16) open from Mar 1 to Jun 30, 2020, in the beginning stages of the pandemic.

Community spread was prevalent in Sweden at that time, and while physical distancing was encouraged, wearing face coverings was not.

Of the 1,951,905 children aged 1 to 16 years in Sweden as of Dec 31, 2019, 65 died in the pre-pandemic period of November 2019 to February 2020, compared with 69 in the pandemic period of March through June 2020. None of the deaths were caused by COVID-19.

Fifteen children diagnosed as having COVID-19, including seven with MIS-C, were admitted to an intensive care unit (ICU) from March to June 2020 (0.77 per 100,000 children in this age-group). Four children required mechanical ventilation. Four children were 1 to 6 years old (0.54 per 100,000), and 11 were 7 to 16 (0.90 per 100,000). Four of the children had an underlying illness: 2 with cancer, 1 with chronic kidney disease, and 1 with a hematologic disease).

Of the country's 103,596 preschool teachers and 20 schoolteachers, fewer than 10 were admitted to an ICU by Jun 30, 2020 (an equivalent of 19 per 100,000). Preschool teachers had an age-adjusted relative risk (RR) of 1.10, compared with occupations other than healthcare, while schoolteachers' RR was 0.43.

In a Karolinska Institute press release, lead author and pediatrician Jonas Ludvigsson, MD, PhD, indicated he was hopeful about the results. "It is very gratifying that serious COVID-19, defined here as needing treatment in an intensive care unit, is so rare among children despite schools being open during the pandemic," he said.

"The next step will be to follow up the children who were treated in an intensive care unit for COVID-19 to see if they have recovered fully. My gut feeling is that children who have been seriously ill because of MIS-C seem to recover fully eventually."

Few primary, no secondary, contact cases in Norway

The third study, published yesterday in Eurosurveillance, was led by researchers at the Norwegian Institute of Public Health in Oslo. From August to November 2020, they traced and twice tested all contacts of 5- to 13-year-old primary school children diagnosed as having COVID-19 and in quarantine in the country's two counties with the highest coronavirus spread.

Thirteen COVID-19 index patients, including eight aged 5 to 10 and five aged 11 to 13, were identified. All index patients but one had household contacts who were confirmed to have COVID-19 before they themselves tested positive.

Four of 13 had gone to school with mild symptoms, but only two contacts had primary cases, and no secondary cases were found. The other index patients were asymptomatic while attending school.

Of the 234 child contacts tested for COVID-19, two primary cases (0.9%) and no secondary cases were found. Of the 58 adult contacts, one primary case (1.7%) and no secondary cases were identified. The median number of contacts per index patient was 19 children and 3 adults.

"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," the authors said.

The researchers concluded that it is better to adjust infection prevention and control protocols according to community transmission levels than to close schools. "The results obtained during low to medium community transmission demonstrate the limited role of children in transmission of SARS-CoV-2 in school settings," they wrote.

"This is an important finding in view of the ongoing discussions on school closures and use of quarantine for a large number of children."

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