A study published yesterday in The Lancet Child & Adolescent Health finds that few children aged 5 months to 4 years attending 22 daycare centers in France from March to May 2020 had SARS-CoV-2 antibodies in their blood, suggesting a 3.7% rate of COVID-19 infection.
The retrospective study, the first to have focused on seroprevalence in daycare centers, was led by researchers from Jean Verdier Hospital in Bondy, France. Fourteen of 327 children (4.3%) and 14 of 197 staff members (7.7%) tested at daycare centers that remained open during France's first lockdown had SARS-CoV-2 antibodies in their blood, versus 9 of 164 adult comparators (5.5%) from Jun 4 to Jul 3. Adjusted seroprevalence was 3.7%, 6.8%, and 5.0%, respectively.
The daycare centers that remained open were reserved for children of essential workers, such as healthcare professionals. Twenty centers were located in the Paris region, and one each were in cities less affected by coronavirus, Rouen in Normandy and Annecy in the Alps. No study participants tested positive for active COVID-19 infection.
"Our results suggest that daycare centres are not focus points of SARS-CoV-2 virus infection and that young children are not spreading the virus widely in these environments," study coauthor Camille Aupiais, PhD, of Jean Verdier Hospital, said in a Lancet press release.
"These findings should be reassuring for parents and staff at daycare centres, especially given that the children included in the study have parents who are keyworkers and are thought to be at higher risk during the first wave of the epidemic."
Household exposures most likely source
Children with SARS-CoV-2 antibodies were more likely than those without antibodies to have been exposed to an adult household member infected with COVID-19 (6 of 14 [43%] vs 19 of 307 [6%]; relative risk [RR], 7.1), suggesting that they weren't infected at school. The authors noted that the children were at higher risk of family spread owing to their parents' occupational exposures to the virus.
Each day, 8 to 56 children attended each center. The centers, which were operated by public hospitals or local councils, mandated universal face coverings, cohorted children and staff in small groups, regularly took temperatures, sent feverish or ill children home, and emphasized hygiene and physical distancing.
Daycare centers that had sent symptomatic children home during lockdown were not associated with higher rates of seropositivity than those that didn't. The 14 children with SARS-CoV-2 antibodies attended 13 different centers, and in the center with two seropositive cases, the children had been in different cohorts. Children at daycare centers with one or more seropositive staff members were more likely to be seropositive (RR, 1.9).
Six of the 14 seropositive children (4%) had no symptoms during lockdown, while 8 (57%) had mild symptoms such as fever, runny nose, cough, abdominal symptoms, or a combination. Among the eight children with antibodies, symptoms, and at least one seropositive parent, five developed symptoms 4 to 10 days after their parents became ill.
The 14 seropositive daycare workers worked at eight different centers, with three each at two centers. While the risk of COVID-19 infection didn't increase after contact with an infected child, the relative risk after exposure to an infected adult household member was high, at 13.1. None of the 185 daycare workers with information on symptoms had a fever, but 40 (22%) reported symptoms.
These research findings, the authors said, are in line with those of a previous US study done in spring 2020 "showing that daycare workers whose centres remained open did not have a greater risk of contracting COVID-19 than daycare workers whose centres closed."
Different testing criteria in young kids proposed
Seropositive adults in the comparator group, who were made up of hospital employees without direct patient contact, were more likely than seronegative adults to have had contact with an infected adult household member. Modeling studies had estimated a 10% COVID-19 infection rate in Paris at the time, and the national seroprevalence rate was 3.3% among adults and 1.6% in children younger than 9 years.
"Our results also suggest that exposure to children who had SARS-CoV-2 infection did not result in an increased risk of infection among daycare centre staff, compared with occupationally unexposed adults," the authors said. "An exploratory analysis comparing seronegative and seropositive adults suggested that the seropositive adults had mostly contracted SARS-CoV-2 infection from another household member."
The authors noted that previous studies have found that children 17 years and younger make up only 1% to 8% of COVID-19 cases and 2% to 4% of those hospitalized and only rarely require intensive care, supplemental oxygen, or ventilation.
The study results suggest that very young children should be tested for infection on the basis of a confirmed household infection rather than clinical signs, they added, although further research is needed in other settings and in light of the relatively recent emergence of more transmissible variants.
"Contact tracing and screening tests must start with parents, other adult household members, and staff at the daycare centre," the authors said. "Further sero-epidemiological studies are needed to determine the extent of SARS-CoV-2 infection among children and to define the role of children in viral transmission."