Youngest Kids More Likely to Spread SARS-CoV-2 to Family: Study

Michele Cohen Marill

August 16, 2021

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Young children are more likely than 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 today in JAMA Pediatrics, found that teenagers (14- to 17-year-olds) were more likely than their younger siblings to bring the virus into the household, while infants and toddlers (up to age 3) were about 43% more likely than the older teens to spread it to others in the home.

Children or teens were the source of SARS-CoV-2 in about one in 13 Ontario households between June and December 2020, the study shows. Researchers from Public Health Ontario analyzed health records from 6280 households with a pediatric COVID-19 case and a subset of 1717 households in which a child up to age 17 was the source of transmission in a household.

When analyzing the data, 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 Sam 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 in families, since it only included symptomatic cases as the initial source and young children are more likely to be asymptomatic, 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 co-infection 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 conclude.

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, noted 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, 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 write.

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, Tennessee.

"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."

What Can Be Done

What can be done, then, to reduce the household spread of COVID-19? "The obvious solution to protect a household with a sick young infant or toddler is to make sure that all eligible members of the household are vaccinated," Coffin and Rubin state in their commentary.

The American Academy of Pediatrics recently wrote Janet Woodcock, MD, acting commissioner of the US Food and Drug Administration, asking for the agency to authorize use of SARS-CoV-2 vaccines for children under age 12 "as soon as possible," noting that "the Delta variant has created a new and pressing risk to children and adolescents across this country, as it has also done for unvaccinated adults."

The FDA reportedly asked vaccine makers Pfizer and Moderna to expand the clinical trials of children, which may delay authorization for younger age groups. Pfizer has said it plans to submit a request for emergency use authorization of its vaccine for 5- to 11-year-olds in September or October.

As with adult vaccination, hesitancy is likely to be a barrier. Less than half of parents said they are very or somewhat likely to have their children get a COVID vaccine, according to a national survey conducted by researchers at the University of California, Los Angeles.

The Ontario study provides valuable evidence to support taking steps to protect children from transmission in schools, including mask requirements, frequent testing, and improved ventilation, said Scarpino.

"We're not going to be able to control COVID without vaccinating younger individuals," he said.

JAMA Pediatr. Published online August 16, 2021. Study, Commentary

Pavia has consulted for GlaxoSmithKline on non-COVID-related issues. Sarah Buchan, PhD, study author and scientist at Public Health Ontario, reported grants from the Canadian Institutes of Health Research for research on influenza, RSV, and COVID-19, and grants from the Canadian Immunity Task Force for COVID-19 outside the submitted work. Coffin reported grants as a Centers for Disease Control and Prevention co-investigator at a Vaccine and Treatment Evaluation Unit site conducting COVID vaccine trials in children. Scarpino holds unexercised options in ILiAD Biotechnologies, which is focused on the prevention and treatment of pertussis. Schaffner is a consultant for VBI Vaccines.

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