The role played by school children in transmitting severe Coronavirus 2 (SARS-CoV-2) infection is a controversial issue in many countries. Although infection rates can be high in children, they rarely develop severe symptoms or health outcomes in the 2019 coronavirus disease (COVID-19). Despite this, schools in many countries were closed during the first wave of the pandemic to contain the transmission of the virus, which resulted in disruption of education for more than 1.5 billion students worldwide.
Analyzing longitudinal changes in SARS-CoV-2 seroprevalence and clustering in Zurich schoolchildren during the first and second waves of the pandemic
Researchers from Switzerland recently presented the results of a longitudinal cohort study they conducted in the city of Zurich. The main objectives of this prospective cohort study were to analyze longitudinal changes in SARS-CoV-2 seroprevalence and assess seropositive groupings of children in school classes from June to November 2020 in Zurich, Switzerland.
Switzerland was one of the countries most affected by the second wave of the SARS-CoV-2 pandemic during the fall of 2020 in Europe. Because schools in Switzerland remain open, they offer a moderate to high exposure environment for studying SARS-CoV-2 infection. Children were randomly selected from different schools and classes, stratified by district, and invited for SARS-CoV-2 serological testing. Parents of selected children completed questionnaires on health and questions related to sociodemography.
Research participants came from 275 classes in 55 schools. A total of 2,603 children participated in the study in June-July 2020, and 2,552 children in October-November 2020. The age range of children was between 6 and 16 years. The main outcomes measured included SARS-CoV-2 seroprevalence in June-July and October-November 2020, seropositive grouping of children in classes, and presence of symptoms in children.
The seroprevalence of SARS-CoV-2 was 2.4% in summer and 4.5% in late fall
In June-July 2020, 74 seropositive children out of 2,496 children had serological results available. In October-November 2020 the number of seropositive children increased to 173 from 2,503 children. Overall, the seroprevalence of SARS-CoV-2 in summer was 2.4% and in late fall 4.5% in previously non-seropositive children. This resulted in a total of 7.8% of the children being seropositive. Seroprevalence varies across districts. In fall, it’s between 1.7 and 15.0%.
No significant differences were observed between lower, middle, and upper school levels or between children aged 6-9 years, 9-13 years, and 12-16 years. Of the 2,223 children tested in the summer and fall, 28/70 or 40% of previously seropositive children became seropositive, and 109 / 2,153 or 5% of previously seropositive children became seropositive. 22% of seronegative children and 29% of new seropositive children since summer showed symptoms. The ratio of children with SARS-CoV-2 infection to seropositive children was 1 in 8 between July and November 2020.
At least one child was detected in 47 of 55 schools and in 90 of 275 new seropositive classes. Of the 130 classes with high enrollment rates, no seropositive children were found in 73 or 56% of the classes; 1 or 2 seropositive children in 50 grades (38%), and at least 3 seropositive children in 7 classes (5%). In a stratified logistic regression model, the school level explains 8% and the grade level explains 24% the seropositive variant.
The findings indicated that the SARS-CoV-2 cohort infection was rare in school classrooms
With schools in Switzerland open since August 2020 and several prevention strategies in place, seropositive groupings of children occurred in only a few classes despite a spike in overall seroprevalence during the moderate to high period of SARS-CoV-2 transmission in the community. Whether these findings will differ from the emergence of a new SARS-CoV-2 variant and the dynamic community transmission rates is uncertain.
“Future testing rounds of this study will provide insights into classroom transmission over extended periods during dynamic levels of community transmission and the spread of the new SARS-CoV-2 variant.”
- Ulyte A, Radtke T, Abela IA, Haile SR, Berger C, Huber M et al. Longitudinal clustering and changes in SARS-CoV-2 seroprevalence in schoolchildren in the canton of Zurich, Switzerland: prospective cohort study of 55 BMJ 2021 schools; 372: n616 doi: 10.1136 / bmj.n616, https://www.bmj.com/content/372/bmj.n616