Young children are more likely than are their older siblings to transmit SARS-CoV-2 in their households, according to an analysis of public health records in Ontario, Canada – a finding that upends the common belief that children play a minimal role in COVID-19 spread.
The study by researchers from Public Health Ontario, published online in JAMA Pediatrics, found that teenagers (14- to 17-year-olds) were more likely than were their younger siblings to bring the virus into the household, while infants and toddlers (up to age 3) were about 43% more likely than were the older teens to spread it to others in the home.
Children or teens were the source of SARS-CoV-2 in about 1 in 13 Ontario households between June and December 2020, the study shows. The researchers analyzed health records from 6,280 households with a pediatric COVID-19 case and a subset of 1,717 households in which a child up to age 17 was the source of transmission in a household.
When analyzing the data, the researchers controlled for gender differences, month of disease onset, testing delay, and mean family size.
The role of young children in transmission seemed logical to some experts who have been tracking the evolution of the pandemic. “I think what was more surprising was how long the narrative persisted that children weren’t transmitting SARS-CoV-2,” said Samuel Scarpino, PhD, managing director of pathogen surveillance at the Rockefeller Foundation.
Meanwhile, less mask-wearing, the return to school and activities, and the onslaught of the Delta variant have changed the dynamics of spread, said Andrew Pavia, MD, chief of the division of pediatric infectious diseases at the University of Utah.
“Adolescents and high-school-aged kids have had much, much higher rates of infection in the past,” he said. “Now when we look at the rates of school-aged kids, they are the same as high-school-aged kids, and we’re seeing more and more in the preschool age groups.”
Cases may be underestimated
If anything, the study may underestimate the role young children play in spreading COVID-19 in families, since it included only symptomatic cases as the initial source and young children are more likely to be asymptomatic, Dr. Pavia said.
The Delta variant heightens the concern; it is more than twice as infectious as previous strains and has spurred a rise in pediatric cases, including some coinfection with other circulating respiratory diseases, such as respiratory syncytial virus (RSV).
The Ontario study covers a period before vaccination and the spread of the Delta variant. “As the number of pediatric cases increases worldwide, the role of children in household transmission will continue to grow,” the authors concluded.
Following recommended respiratory hygiene is clearly more difficult with very young children. For example, parents, caregivers, and older siblings aren’t going to stay 6 feet away from a sick baby or toddler, Susan Coffin, MD, MPH, a pediatric infectious disease physician, and David Rubin, MD, a pediatrician and director of PolicyLab at Children’s Hospital of Philadelphia, noted in an accompanying commentary.
“Cuddling and touching are part and parcel of taking care of a sick young child, and that will obviously come with an increased risk of transmission to parents as well as to older siblings who may be helping to care for their sick brother or sister,” they wrote.
While parents may wash their hands more frequently when caring for a sick child, they aren’t likely to wear a mask, said William Schaffner, MD, an infectious disease specialist at Vanderbilt University, Nashville, Tenn.
“I imagine some moms even take a sick child into bed with them,” he said. “It’s probably just the extensive contact one has with a sick, very small child that augments their capacity to transmit this infection.”