Young kids more likely than older kids to spread COVID-19 to household

A Canadian study today in JAMA Pediatrics suggests that while younger children are less likely than older children to be the index COVID-19 patient in their home, they are more likely to spread it to household members.

Led by researchers from Public Health Ontario in Toronto, the study involved 6,280 households with COVID-19 index patients 17 years and younger from Jun 1 to Dec 31, 2020.

Of the 6,280 households, 1,717 (27.3%) experienced SARS-CoV-2 transmission to a median of two siblings or caregivers in the household 1 to 14 days after index patient diagnosis. Children aged 0 to 8 had higher odds of transmitting the virus, but those 3 years and younger had the greatest infectivity (odds ratio [OR], 1.43 vs those 14 to 17 years).

Similar odds were seen when restricting secondary cases to those occurring 2 to 14 days or 4 to 14 days after diagnosis of the index patient, regardless of symptoms or link to a school or childcare outbreak or reopening.

Consistent with increasing degrees of autonomy, proportions of index patients in each age-group rose with age, with 12% of those 0 to 3 years, 20% of those 4 to 8, 30% of those 9 to 13, and 38% of those 14 to 17. Mean COVID-19 index patient age was 10.7 years, and 45.6% were girls.

Testing delays, larger family sizes

Children of all ages most often spread SARS-CoV-2 to household members 20 years or younger or 30 to 50 years old. When analyzing data on just older children, however, the authors found that they tend to transmit infection to older adults in those age-groups.

Also, children 4 to 8 and 9 to 13 years were less likely than those 0 to 3 or 14 to 17 to have no symptoms.

Kids were more likely to spread the coronavirus amid COVID-19 testing delays (OR for 1-day delay, 1.24 vs 2.98 for 5 or more days). Larger family size also increased the chances of transmission (OR, 1.63 per person increase).

The study authors noted that because there were fewer COVID-19 diagnoses in children than in adults amid lockdowns and limited testing capacity early in the pandemic, pediatric household transmission hasn't been well characterized. In addition, household studies have typically compared spread among only young versus old patients, potentially missing more granular differences among age-groups.

But because the number of pediatric COVID-19 diagnoses has risen since jurisdictions eased public health measures and reopened schools in fall 2020, more data are now available to better elucidate child-to-household virus spread.

Vaccination of eligible household members

The findings, the authors said, suggest that household members, schools, and childcare facilities need to consider the differential infectivity of pediatric age-groups.

"Although children do not appear to transmit infection as frequently as adults, caregivers should be aware of the risk of transmission while caring for sick children in the household setting," the researchers wrote. "As it is challenging and often impossible to socially isolate from sick children, caregivers should apply other infection control measures where feasible, such as use of masks, increased hand washing, and separation from siblings."

In an editorial in the same journal, Susan Coffin, MD, MPH, and David Rubin, MD, MSCE, both of the University of Pennsylvania School of Medicine, said that sick infants and toddlers may be more likely to spread SARS-CoV-2 to household members than older children because they require close contact with their caregivers.

Because physical distancing and continual masking is unlikely in such settings, Coffin and Rubin recommended vaccination of eligible household members. "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," they said.

"Cloaked with the protection of vaccine, household members need not fear the youngest family members with a runny nose come fall; the solution—vaccination—is now within their grasp."

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