Studies Showing Schools Aren’t a Significant Source of COVID-19 Transmission
Here’s a running list of studies showing that K-12 schools aren’t a significant source of COVID-19 transmission.
1. Official Journal of the American Academy of Pediatrics [February 20, 2021]
TITLE: COVID-19 Transmission in US Child Care Programs
METHODS: “Data were obtained from U.S. child care providers (N=57,335) reporting whether they had ever tested positive or been hospitalized for COVID-19 (N=427 cases), along with their degree of exposure to child care. Background transmission rates were controlled statistically, and other
demographic, programmatic, and community variables were explored as potential confounders. Logistic regression analysis was used in both unmatched and propensity score matched case control analyses.”
CONCLUSION: “No association was found between exposure to child care and COVID-19 in both unmatched (odds ratio [OR], 1.06; 95% confidence interval [CI], 0.82 to 1.38) and matched (OR, 0.94; 95% CI, 0.73 to 1.21) analyses. In matched analysis, being a home-based provider (as opposed to center-based) was associated with COVID-19 (OR, 1.59; 95% CI, 1.14 to 2.23), but showed no interaction with exposure.”
2. Official Journal of the American Academy of Pediatrics [January 8, 2021]
TITLE: Incidence and Secondary Transmission of SARS-CoV-2 Infections in Schools
METHODS: “From 08/15/2020–10/23/2020, 11 of 56 school districts participating in ABCs were open for in-person instruction for all 9 weeks of the first quarter and agreed to track incidence and secondary transmission of SARS-CoV-2. Local health department staff adjudicated secondary transmission. Superintendents met weekly with ABCs faculty to share lessons learned and develop prevention methods.”
CONCLUSION: “Over 9 weeks, 11 participating school districts had more than 90,000 students and staff attend school in-person; of these, there were 773 community-acquired SARS-CoV-2 infections documented by molecular testing. Through contact tracing, NC health department staff determined an additional 32 infections were acquired within schools. No instances of child to adult transmission of SARS-CoV-2 were reported within schools.”
“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.”
3. The Lancet [August 2020]
TITLE: Transmission of SARS-CoV-2 in Australian educational settings: a prospective cohort study
METHODS: “Laboratory-confirmed paediatric (aged ≤18 years) and adult COVID-19 cases who attended a school or ECEC setting while considered infectious (defined as 24 h before symptom onset based on national guidelines during the study period) in NSW from Jan 25 to April 10, 2020, were investigated for onward transmission. All identified school and ECEC settings close contacts were required to home quarantine for 14 days, and were monitored and offered SARS-CoV-2 nucleic acid testing if symptomatic. Enhanced investigations in selected educational settings included nucleic acid testing and SARS-CoV-2 antibody testing in symptomatic and asymptomatic contacts. Secondary attack rates were calculated and compared with state-wide COVID-19 rates.”
CONCLUSION: “15 schools and ten ECEC settings had children (n=12) or adults (n=15) attend while infectious, with 1448 contacts monitored. Of these, 633 (43·7%) of 1448 had nucleic acid testing, or antibody testing, or both, with 18 secondary cases identified (attack rate 1·2%). Five secondary cases (three children; two adults) were identified (attack rate 0·5%; 5/914) in three schools. No secondary transmission occurred in nine of ten ECEC settings among 497 contacts. However, one outbreak in an ECEC setting involved transmission to six adults and seven children (attack rate 35·1%; 13/37). Across all settings, five (28·0%) of 18 secondary infections were asymptomatic (three infants [all aged 1 year], one adolescent [age 15 years], and one adult).
“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. These findings could be used to inform modelling and public health policy regarding school closures during the COVID-19 pandemic.“
4. Eurosurveillance [January 2021]
TITLE: Minimal transmission of SARS-CoV-2 from paediatric COVID-19 cases in primary schools, Norway, August to November 2020
METHODS: An index case was defined as a case aged 5–13 years in Oslo or Viken county with PCR-confirmed SARS-CoV-2 infection, who had attended school within 48 hours before symptom onset or date of sampling. We prospectively included contact tracings around 13 index cases. For each index case, public health officials identified exposed child and adult school contacts. All consenting cases and contacts delivered two self-collected saliva samples; the first was collected as soon as possible after they were identified, and the second was collected at the end of their 10-day quarantine period. We excluded contact tracings with adult COVID-19 index cases.
CONCLUSION: Thirteen contact tracings from primary schools were included: eight in the age group 5–10 years old (grades 1–4) and five in the age group 11–13 years old (grades 5–7). A total of 13 index cases and 292 school contacts participated in the study. In Contact Tracing 7, the index case did not consent to participate and saliva samples from this individual could not be collected. In Contact Tracing 8, two index cases were included, and in all the remaining 11 contact tracings one index case was included. Four of the 13 index cases had attended school with mild symptoms (in Contact Tracings 2, 3, 4 and 13); however, among these four index cases’ contacts, only two primary cases (both in Contact Tracing 13) and no secondary case was identified. The remaining index cases were asymptomatic while attending school. All index cases, except one, had household members who were diagnosed with COVID-19 before the index cases themselves tested positive.
“Among the 234 child contacts that were tested for SARS-CoV-2, two primary cases (0.9%) and no secondary cases were identified, and among the 58 adult contacts one primary case (1.7%) and no secondary cases were detected. The three primary cases were identified in two different contact tracings.“
5. Centers for Disease Control and Prevention [January 29, 2021]
TITLE: COVID-19 Cases and Transmission in 17 K–12 Schools — Wood County, Wisconsin, August 31–November 29, 2020
METHODS: “The coronavirus disease 2019 (COVID-19) pandemic has disrupted in-person learning in the United States, with approximately one half of all students receiving online-only instruction since March 2020.* Discontinuation of in-person schooling can result in many hardships (1) and disproportionately affects families of lower socioeconomic status (2). Current evidence suggests that transmission of SARS-CoV-2, the virus that causes COVID-19, in kindergarten through grade 12 (K–12) schools might not significantly contribute to COVID-19 spread nationwide (3). During August 31–November 29, 2020, COVID-19 cases, spread, and compliance with mask use were investigated among 4,876 students and 654 staff members who participated in in-person learning in 17 K–12 schools in rural Wisconsin. School-attributable COVID-19 case rates were compared with rates in the surrounding community. School administration and public health officials provided information on COVID-19 cases within schools. During the study period, widespread community transmission was observed, with 7%–40% of COVID-19 tests having positive results. Masking was required for all students and staff members at all schools, and rate of reported student mask-wearing was high (>92%). COVID-19 case rates among students and staff members were lower (191 cases among 5,530 persons, or 3,453 cases per 100,000) than were those in the county overall (5,466 per 100,000). Among the 191 cases identified in students and staff members, one in 20 cases among students was linked to in-school transmission; no infections among staff members were found to have been acquired at school. These findings suggest that, with proper mitigation strategies, K–12 schools might be capable of opening for in-person learning with minimal in-school transmission of SARS-CoV-2.”
CONCLUSION: “This study, involving students and staff members in 17 K–12 schools in five rural Wisconsin districts under district and statewide mask mandates, found high teacher-reported student masking compliance. Among 5,530 students and staff members, 191 COVID-19 cases were reported. Only seven (3.7%) of these cases were associated with in-school transmission, all in students. Despite widespread community transmission, COVID-19 incidence in schools conducting in-person instruction was 37% lower than that in the surrounding community.
Children might be more likely to be asymptomatic carriers of COVID-19 than are adults (4). In the present study, the absence of identified child-to-staff member transmission during the 13-week study period suggests in-school spread was uncommon. This apparent lack of transmission is consistent with recent research (5), which found an asymptomatic attack rate of only 0.7% within households and a lower rate of transmission from children than from adults. However, this study was unable to rule out asymptomatic transmission within the school setting because surveillance testing was not conducted.
Student masking compliance was reported to exceed 92% throughout the course of the study. Older children were reported to be equally compliant with masking as younger children. High levels of compliance, small cohort sizes (maximum of 20 students), and limited contact between cohorts likely helped mitigate in-school SARS-CoV-2 transmission and could be responsible for the low levels of transmission detected in schools. Investigation of 191 school-related COVID-19 cases in students and staff members suggested that most transmission occurred outside of required school activities. This finding is consistent with recently reported data suggesting limited transmission within schools (6).
6. Eurosurveillance [May 2020]
TITLE: No evidence of secondary transmission of COVID-19 from children attending school in Ireland, 2020
METHODS: “To find evidence in the Republic of Ireland on COVID-19 transmissions related to schools before their closure, all SARS-CoV-2 notifications to Public Health Departments were screened to identify children, under the age of 18 years, and adults who had attended the school setting.
“Cases were identified within the Computerised Infectious Disease Reporting (CIDR) system (Ireland’s national infectious disease surveillance system). On CIDR, attendance at work or school was routinely recorded for COVID-19 surveillance. Contact-tracing records and records from active surveillance were reviewed to identify cases of secondary transmission.”
CONCLUSION: “In summary, examination 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.
“The only documented transmission that occurred from this cohort was between adults in a working environment outside school. Among 1,025 child and adult contacts of these six cases in the school setting there were no confirmed cases of COVID-19 during the follow-up period. Follow-up period was at least one incubation period (14 days) from last contact with a case.“
7. The Journal of Public Health Management and Practice [Dec. 30, 2020]
TITLE: Data-Driven Reopening of Urban Public Education Through Chicago’s Tracking of COVID-19 School Transmission
METHODS: “The Archdiocese reported individual suspect and confirmed COVID-19 cases through a schoolfocused confidential online case report form, and the youth settings response team provided case management support by phone as needed. The Archdiocese conducted ongoing quality assurance regarding implementation of mitigation strategies and sent 2 reminders by system e-mail listserv regarding following public health guidance outside of school throughout the study period. School-associated cases were defined as confirmed or probable COVID-19 cases (based on the CDC COVID-19 Interim Case Definition, approved August 5, 2020) that occurred when school was in session AND one of the following: The case was in the school during his or her infectious period (2 days prior to symptom onset or test date through 10 days after his or her
symptom onset or test date); or
Non–school-associated cases were removed from the analysis, as they would not have exposed the school and could not have contributed to transmission. School-associated cases were reviewed weekly by
the youth settings team to review both the school interview records and the case/family interview records to classify the likely location of transmission (eg, school, household, community, or other). The number of school-associated cases, number of reporting schools by type, number of clusters or outbreaks (defined as ≥2 cases with an epidemiological link within the facility as determined by CDPH facility/case investigation),2 and hypothesized location of transmission for each cluster or outbreak were tracked weekly. Archdiocese school-associated cases from August 17, 2020 (the start date of the Archdiocese school year), to October 4, 2020, and location of transmission as determined by public health investigation were
included in this report.”
CONCLUSION: “Thirty-one Archdiocese schools reported 59 COVID19 cases (20 staff members and 39 students), with 1 to 8 cases reported per school (median: 1). Thirty-three students were considered school-associated cases by CDPH of which 17 (51.5%) Female and 16 (48.5%) Male. Student age range was 4 to 17 years (median age: 10 years). Of staff, CDPH classified 14 as school associated cases.
“Among the total 47 school-associated cases, 3 clusters were identified. Two involved only staff and one involved a student and a staff member. Two of the 3 clusters were associated with nonadherence to physical distancing outside of class time. There was one cluster in which we could not rule out transmission in the classroom setting. When CDPH noted multiple cases at a single school, it was most commonly siblings. The most common locations of transmission for school-reported cases were outside school settings, such as family parties, sports team gatherings, and other out-of-school
social events. The Archdiocese schools’ COVID-19 attack rate from August 17 to October 4, 2020, for students was 0.2% (33 cases among estimated student population of 19 500), while the COVID-19 attack rate for all Chicago children (0-17 years of age) from August 17 to October 4, 2020, was 0.4% (2147 cases among pediatric population of 548 9994). The COVID-19 attack rate for staff was 0.5% (14 cases among an estimated staff population of 2750) lower than the COVID-19 attack rate for working-age adults in Chicago (0.7%; 12 354 cases among a population of working-age adults [18-64 years] of 1 807 2774) within the same time period. This analysis was performed in a background of moderate to high COVID-19 disease incidence citywide but during a plateau in case incidence between Chicago’s first and second waves. From August 17, 2020, to October 4, 2020, citywide, the average 7-day rolling average (7DRA) incident case count was 316 (range, 250-358; equivalent to 9.3-13.3 daily infections per 100 000 population). The average 7DRA test positivity was 4.8% (range, 4.1%-5.3%).
“Data collected in the nationʼs largest Catholic school system suggest that implementation of layered mitigation strategies creates a low- but not zero-risk environment for in-person learning in public schools. Chicago data revealed a lower attack rate for students and school staff than for the city overall during a period of moderate to high COVID-19 incidence. The median number of cases reported per school was also 1, suggesting minimal identifiable in-school transmission and matching our citywide private and charter school case investigation findings.”
8. Acta Pediatrica [May 19, 2020]
TITLE: Children are unlikely to be the main drivers of the COVID‐19 pandemic – A systematic review
METHODS: “A systematic literature review of the MEDLINE and EMBASE databases and medRxiv/bioRxiv preprint servers to 11 May 2020 identified published and unpublished papers on COVID‐19 transmission by children.”
CONCLUSION: “We identified 700 scientific papers and letters and 47 full texts were studied in detail. Children accounted for a small fraction of COVID‐19 cases and mostly had social contacts with peers or parents, rather than older people at risk of severe disease. Data on viral loads were scarce, but indicated that children may have lower levels than adults, partly because they often have fewer symptoms, and this should decrease the transmission risk. Household transmission studies showed that children were rarely the index case and case studies suggested that children with COVID‐19 seldom caused outbreaks. However, it is highly likely that children can transmit the SARS‐COV‐2 virus, which causes COVID‐19, and even asymptomatic children can have viral loads.
“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.”
9. BMJ Pediatric Open [June 21, 2020]
TITLE: Role of children in the transmission of the COVID-19 pandemic: a rapid scoping review
METHODS: “A rapid scoping review was carried out by searching PubMed to know if children are more contagious than adults, and the proportion of asymptomatic cases in children. Google Scholar and MedRxiv/bioRxiv were also searched. The time period was restricted from 1 December 2019 until 28 May 2020. Only studies published in English, Italian, French or Spanish were included.”
CONCLUSION: “Fourteen out of 1099 identified articles were finally included. Studies included cases from China (n=9 to 2143), China and Taiwan (n=536), Korea (n=1), Vietnam (n=1), Australia (n=9), Geneva (n=40), the Netherlands (n=116), Ireland (n=3) and Spain (population-based study of IgG, n=8243). Although no complete data were available, between 15% and 55%–60% were asymptomatic, and 75%–100% of cases were from family transmission. Studies analysing school transmission showed children as not a driver of transmission. Prevalence of COVID-19 IgG antibody in children <15 years was lower than the general population in the Spanish study.
“Children are not transmitters to a greater extent than adults. There is a need to improve the validity of epidemiological surveillance to solve current uncertainties, and to take into account social determinants and child health inequalities during and after the current pandemic.“
10. Clinical Infectious Diseases [June 25, 2020]
TITLE: Novel Coronavirus 2019 Transmission Risk in Educational Settings
METHODS: “In February and March 2020, comprehensive nationwide surveillance and contact tracing as part of Singapore’s public health strategy identified 3 potential SARS-CoV-2 seeding incidents in 3 separate educational settings [4, 5]. There were 2 preschools and 1 secondary school. Clinical and epidemiological data of the confirmed cases and their contacts from school were extracted for analysis.”
CONCLUSION: “Comprehensive surveillance and screening of symptomatic student contacts following exposure to an index COVID-19 student case up to the first day of symptom onset in a secondary school and a preschool setting found no evidence of disease transmission. In addition, screening of both symptomatic and asymptomatic children who were exposed to a major COVID-19 cluster of adult staff members in a separate preschool setting also did not detect any SARS-CoV-2 infection.
“Prior studies showed that the viral load of SARS-CoV-2 infection peaked soon after symptom onset and that it was possible for transmission to occur independent of symptoms. Environmental viral contamination from a generally well pediatric COVID-19 case had also been demonstrated . However, during our investigations, evidence of COVID-19 disease was undetectable among symptomatic contacts in both secondary and preschool settings. In the third transmission study (preschool 2), the attack rates among staff members in the preschool and their households were unsurprisingly high in view of the high R0 and attack rates reported in the community [8, 9]. Despite screening both symptomatic and asymptomatic children in preschool 2, SARS-CoV-2 infection was also undetectable. Taken together, these findings suggest that the risk of SARS-CoV-2 transmission among children in schools, especially preschools, is likely to be low. The only other published school transmission risk study involved a symptomatic 9-year-old child with COVID-19 who attended 3 different schools . Subsequent follow-up and testing of symptomatic children from the preschools also did not detect virus transmission. The reason for this low attack rate among children is unclear. A recent study using single-nucleus multiomic profiling of alveolar epithelial cells found that lung samples from young children expressed fewer genes (ACE2 and TMPRSS2) known to be utilized by SARS-CoV-2 for cell entry . Therefore, children may be more resistant to SARS-CoV-2 infection at a cellular level.”
11. The New England Journal of Medicine [June 11, 2020]
TITLE: Spread of SARS-CoV-2 in the Icelandic Population
METHODS: “We targeted testing to persons living in Iceland who were at high risk for infection (mainly those who were symptomatic, had recently traveled to high-risk countries, or had contact with infected persons). We also carried out population screening using two strategies: issuing an open invitation to 10,797 persons and sending random invitations to 2283 persons. We sequenced SARS-CoV-2 from 643 samples.”
CONCLUSION: “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. (Funded by deCODE Genetics–Amgen.)”
12. Eurosurveillance [September 10, 2020]
TITLE: 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
METHODS: To gain further understanding on paediatric transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the school/childcare-facility context, we compiled and analysed data from SARS-CoV-2 infected children (age: 0–19 years), who had been to school/childcare facilities, after such establishments reopened in Baden-Württemberg in May 2020.
CONCLUSION: There is an ongoing discussion in the scientific community regarding the role of children in the transmission of SARS-CoV-2. Recently, the percentage of children and adolescents up to 19 years old among all COVID-19 cases in Germany has increased to 25%. Infected children are more likely to remain asymptomatic or have a mild course of disease and are much less likely than adults to be hospitalised or have fatal outcomes. Thus, their infection may go undetected or undiagnosed. Symptomatic children seem to shed virus in similar quantities as adults and can infect others in a similar way, but it is unknown how infectious asymptomatic children are.
Our investigation suggests that child-to-child transmission in schools and childcare facilities is uncommon and not the primary cause of SARS-CoV-2 infection in children. Based on our estimation there could be one secondary case per roughly 25 infectious school days. This ratio of 1 in 25 might, however, overestimate the transmission risk in schools and childcare facilities, because some of the 104 index cases (i.e. 104 = 557 − 453) for whom no information on school attendance was available, may also have spent some time in school or in a childcare facility while being infectious, yet without further generating any notified COVID-19 cases. While investigations from Ireland concur with our results, a report from Israel showed a large outbreak in apparently over-crowded schools where face-mask usage had been discontinued due to a heat wave.
The low transmission in schools and childcare facilities found in this current study might be due in part to the infection control measures initiated after school/childcare-facility reopening, yet it is not clear how much the different measures have contributed. In order to gradually return to the regular school and childcare-facility life, larger classes will have to be accepted again. This will require more proximity between pupils. As a countermeasure, strict ventilation of classrooms, not only between lessons but also within, should be implemented. Additionally, face masks should be used in schools, both, inside and outside of classrooms. Based on our current study findings, we anticipate that transmission rates in schools and childcare facilities would remain low under such interventions
13. The British Medical Journal [September 2, 2021]
TITLE: Risk of hospital Admission with Covid-19 among teachers compared with healthcare workers and other adults of working age in Scotland, March 2020 to July 2021: population based case-control study
METHODS: Scotland, March 2020 to July 2021, during defined periods of school closures and full openings in response to covid-19.
All cases of covid-19 in adults aged 21 to 65 (n=132 420) and a random sample of controls matched on age, sex, and general practice (n=1 306 566). Adults were identified as actively teaching in a Scottish school by the General Teaching Council for Scotland, and their household members were identified through the unique property reference number. The comparator groups were adults identified as healthcare workers in Scotland, their household members, and the remaining general population of working age.
CONCLUSION: Most teachers were young (mean age 42), were women (80%), and had no comorbidities (84%). The risk (cumulative incidence) of hospital admission with covid-19 was <1% for all adults of working age in the general population. Over the study period, in conditional logistic regression models adjusted for age, sex, general practice, race/ethnicity, deprivation, number of comorbidities, and number of adults in the household, teachers showed a lower risk of hospital admission with covid-19 (rate ratio 0.77, 95% confidence interval 0.64 to 0.92) and of severe covid-19 (0.56, 0.33 to 0.97) than the general population. In the first period when schools in Scotland reopened, in autumn 2020, the rate ratio for hospital admission in teachers was 1.20 (0.89 to 1.61) and for severe covid-19 was 0.45 (0.13 to 1.55). The corresponding findings for household members of teachers were 0.91 (0.67 to 1.23) and 0.73 (0.37 to 1.44), and for patient facing healthcare workers were 2.08 (1.73 to 2.50) and 2.26 (1.43 to 3.59). Similar risks were seen for teachers in the second period, when schools reopened in summer 2021. These values were higher than those seen in spring/summer 2020, when schools were mostly closed.
“Compared with adults of working age who are otherwise similar, teachers and their household members were not found to be at increased risk of hospital admission with covid-19 and were found to be at lower risk of severe covid-19. These findings should reassure those who are engaged in face-to-face teaching.“
Feature image: Dan Gaken
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