Study: COVID-19 spreads fastest among teens and tweens

A comprehensive new study from South Korea challenged widely held beliefs that school-age children were less likely to get infected and therefore less likely to spread the virus.

The findings could add to the growing conversation about safely opening schools in the U.S. amid the pandemic. 

A study by South Korean researchers found older kids (ages 10-19) were are more likely to spread Covid-19 within a household than younger children and adults.

The study involving almost 65,000 people found that children between the ages of 10 and 19 can spread the virus at least as easily as, if not more readily than adults can. Among kids younger than 10, while transmission rates were significantly lower than adults, there was still a risk. They were about half as likely as adults to spread the virus to others, researchers said. 

South Korea has been lauded for its efforts to mitigate the spread of the virus, with policies that included mass production and distribution of face masks, widespread testing, and rigorous contact tracing.

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As part of their study, South Korean researchers identified 5,706 people who were the first to report COVID-19 symptoms in their households (index patients) between Jan. 20 and March 27, when schools were closed due to the virus. Researchers then identified the index patients' 59,073 contacts and monitored them for an average of about 10 days after infection was detected. They tested all of the household contacts of each patient.

"We detected COVID-19 in 11.8% of household contacts,” researchers said, adding, "rates were higher for contacts of children than adults." 

The study said in the middle of school closures, the highest rate of infections (18.6%) was seen for household contacts of older school-age children, 10-19 years old. The group was shown to be even more likely to infect others than adults were. The lowest COVID-19 rate (5.3%) for household contacts was seen among younger children 0–9 years old. 

"These risks largely reflected transmission in the middle of mitigation and therefore might characterize transmission dynamics during school closure,” researchers said, adding, "Young children may show higher attack rates when the school closure ends, contributing to community transmission of COVID-19."

Researchers pointed to the limitations of their analysis, including the fact that the number of infected cases might have been underrepresented because all asymptomatic patients might not have been identified. Also, detected cases could have resulted from exposure outside the household.

But they said the findings underscored the importance of contact tracing and how household transmission played a critical role in the spread of the virus. And they also pointed to the importance of implementing health recommendations within affected households, including handwashing and even masks.

While the study did not offer any definitive answers about opening schools, experts said the findings showed how cases of infection among kids attending school could increase virus levels in the wider community, triggering more outbreaks.