Many children who were seropositive for SARS-CoV-2 antibodies had tested negative earlier or had not undergone testing for Covid-19, according to the results of the EnCORE (Enfants et COVID-19: Étude de séroprévalence) study from Canada. Seropositivity increased from 5.8% at baseline to 8.4% at the end of the study.

The study recruited 1632 children, 2 to 17 years of age, from four neighborhoods of Montreal, Canada to detect the seroprevalence of SARS-CoV-2 antibodies between October 2020 and March 2021. Montreal was one of the worst affected cities during the first and second wave of the pandemic. The study sample was obtained from day care centers, primary and secondary schools. The finger-pricked dried blood spot (DBS) specimens were collected by parents, who also answered an online questionnaire on self-reported COVID-19 symptoms and tests. Boys comprised 51% of the study population. Almost 80% of the children were normal weight or underweight and 94% had no underlying medical condition.

Ninety-five children were seropositive for SARS-CoV-2 antibodies; 46 (48%) had no symptoms and 49 (52%) had only mild Covid-19 symptoms. 78 (82%) of them had either never been tested before or had tested negative on RT-PCR. The overall baseline seroprevalence of SARS-CoV-2 in this sample of population was 5.8%; this increased over the course of the pandemic, from 3.2% between October and November 2020 and 8.4% between March and April 2021. Children in secondary schools had the highest seroprevalence at 6.7%. Children who had a family member in healthcare were more likely to be seropositive. Only 18% of seropositive participants had earlier tested positive for SARS-CoV-2 establishing “the value of serology as a tool for SARS-CoV-2 surveillance.” No association of seropositivity with age was observed.

These findings suggest that children were being infected even though they were asymptomatic or had only mild symptoms. And, not all children with Covid-19 were detected by RTPCR. This study validates the earlier observation of children as a potential source of infection for their families as well as the community. It further highlights the importance of serosurveillance in this population group given the emergence of new variants of concern and the fact that vaccination for children is yet to begin in many parts of the world.

Reference

1. Zinszer K, et al. Seroprevalence of SARS-CoV-2 antibodies among children in school and day care in Montreal, Canada. JAMA Netw Open. 2021 Nov 1;4(11):e2135975. doi: 10.1001/jamanetworkopen.2021.35975.