In a first-of-its-kind study estimating antibodies from the viral infection that causes COVID-19 in preschool settings, French researchers found the rate of infection in children to be as low as 3.7%, reinforcing previous research suggesting day care centers remained relatively safe during the pandemic.

The study, published Monday in The Lancet Child & Adolescent Health, aims to provide clarity on the extent to which children contribute to SARS-CoV-2 transmission by estimating antibodies in the blood, also known as seroprevalence. 

Researchers enrolled 327 children aged between 5 months and 4 years old, along with 197 staff members who attended one of 22 day care centers during the first national lockdown in France from March to May 2020. As part of the seroprevalence study, testing was conducted four to eight weeks post-lockdown. 

Study author Camille Aupiais noted that almost all nurseries and schools were closed until early May except for a few nurseries that remained open to the children of essential workers, which were mainly hospital and social workers. 

“After that first lockdown, we thought that it would be interesting to know if those children and the staff that took care of those children were infected during that first wave,” added Aupiais, who is also a pediatrician at Jean Verdier Hospital in Paris.

Low rates of 4.2% and 7.1% of antibodies were observed among enrolled children and day care center staff, respectively. These dropped to 3.7% in children and 6.8% in staff members after accounting for imperfect sensitivity and specificity of the Abbott RealTime SARS-CoV-2 assay, the most widely used COVID-19 test.

The researchers at Assistance Publique - Hôpitaux de Paris reported a similar seroprevalence rate of 5% in an additional 164 adult hospital workers not exposed to children who formed a comparator group. 

“We can conclude that the nurseries that remained opened were not a place of high circulation,” Aupiais said, adding, “We think it could help to reassure the parents and the staff of those nurseries” and policymakers make decisions around in-person schooling.

The study adds to a growing body of research offering reassurance to parents about the safety of day care centers. It supports previous research pointing to transmission in the home or via a family member as more plausible, as opposed to in schools. This is in contrast with widespread concerns at the start of the COVID-19 pandemic that children could be potential vectors of transmission because they are known to be strong contributors to the spread of respiratory diseases like seasonal influenza. 

The research also provides insight into efforts worldwide to strike the right balance between protecting public health and allowing children to attend school in person during the COVID-19 pandemic. It suggests that the latter is safe where special precautions, including the use of face masks, hygiene and social distancing measures, among others, have been adopted. 

The study also adds fuel to the debate about keeping nurseries open during future waves of the COVID-19 pandemic. 

“Our study plus other studies support keeping schools open,” Aupiais says. But she notes that there is a need for additional seroprevalence studies to be conducted in school settings to apply the study findings more widely. 

The article, “SARS-CoV-2 transmission among children and staff in daycare centres during a nationwide lockdown in France: a cross-sectional, multicentre, seroprevalence study,” was published Feb. 8 in The Lancet Child & Adolescent Health. The authors of the study were Eric Lachassinne, Loïc de Pontual, Marion Caseris, Mathie Lorrot, Carole Guilluy, Aurélie Naud, Marie-Aliette Dommergues, Didier Pinquier, Evelyne Wannepain, Elisabeth Hausherr, Camille Jung, Vincent Gajdos, Robert Cohen, Jean-Ralph Zahar, Ségolène Brichler, Romain Basmaci, Pierre-Yves Boelle, Coralie Bloch-Queyrat, and Camille Aupiais, Assistance Publique - Hôpitaux de Paris.