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July 21, 2020

Study finds older children transmit the new coronavirus just as much as adults

Daily Briefing

    Children ages 10 to 19 spread the new coronavirus at the same rate as adults, according to a large study recently published in Emerging Infectious Diseases, and public health experts say the findings should be taken into account as state and local officials consider whether to reopen U.S. schools this fall.

    Will it be safe for children to go back to school this fall?

    Study details

    For the study—which was published online as an early release, meaning there could be changes to the study before it is officially released—researchers from South Korea identified 5,706 people who were the first in their households to report symptoms of Covid-19, the disease caused by the novel coronavirus, between Jan. 20 and March 27. The researchers then traced a total of 59,073 contacts of those 5,706 index patients, including both household and non-household contacts. The researchers tested all of the index patients' household contacts for the coronavirus, regardless of whether the contacts showed symptoms of Covid-19. The researchers tested the index patients' non-household contacts for the virus only if those contacts experienced symptoms of Covid-19.

    The researchers found that, of the index patients' 10,592 household contacts, 11.8% were infected with the coronavirus. Of the index patients' 48,481 non-household contacts, 1.9% were infected with the virus, according to the study.

    When looking at index patients by age group, the researchers found that the transmission rate to patients' household contacts was about 5.3% among patients ages 0 to 9, making them the least likely age group to spread the coronavirus to others in their households, and about 18.6% among children ages 10 to 19, making them the most likely age group to spread the virus to others in their households. The second-most likely group to spread the coronavirus to their household contacts were index patients ages 70 to 70, with a transmission rate of about 18%, the researchers found.

    The researchers acknowledged that the first person to show Covid-19 symptoms in a household may not be the first person infected with the virus, and that children are less likely than adults to experience symptoms of Covid-19. That means the true number of coronavirus cases among both children and adults may have been undercounted, the researchers said.

    However, the researchers said their findings suggest that children, and particularly children ages 10 to 19, could contribute to community transmission of the novel coronavirus if they attend school. Further, they wrote, "Although the detection rate for contacts of preschool-aged children was lower, young children may show higher attack rates" if they attend school, also "contributing to community transmission."

    Overall, the researchers wrote, "The role of household transmission of [the new coronavirus] amid reopening of schools and loosening of social distancing underscores the need for a time-sensitive epidemiologic study to guide public health policy," as well as robust contact tracing and other precautions to prevent the virus' spread.

    'There will be transmission'

    The study's results come amid a nationwide debate over whether U.S. schools should reopen this fall, an issue that has divided experts as America's coronavirus epidemic in recent weeks has resurged to new peaks.

    Some early studies from Europe and Asia have suggested that younger children don't spread the new coronavirus as much as adults and are less likely to contract the virus, but those studies have been small and flawed, according to Ashish Jha, director of the Harvard Global Health Institute. In comparison, the new study from South Korea "is very carefully done, it's systematic and looks at a very large population," Jha said. "It's one of the best studies we've had to date on this issue," he added.

    However, Caitlin Rivers, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, who helped to craft a scientific panel's recent recommendation that U.S. schools reopen, said because the South Korean researchers only traced the contacts of symptomatic children for their study, it doesn't provide evidence on whether asymptomatic children spread the novel coronavirus, which is a key outstanding question.

    "I think it was always going to be the case that symptomatic children are infectious," Rivers said. "The questions about the role of children are more around whether children who don't have symptoms are infectious."

    Jeffrey Shaman, an epidemiologist at Columbia University's Mailman School of Public Health, said it's difficult "trying to find the right balance" of ensuring that children don't miss out on the important education and socialization they receive in school while also keeping students, parents, and teachers safe, because children likely will transmit the virus if they return to school.

    "So long as children are not just a complete dead end—incapable of passing the virus on, which does not seem to be the case—putting them together in schools, having them mix with teachers and other students will provide additional opportunities for the virus to move from person to person," he said.

    Michael Osterholm, an infectious disease expert at the University of Minnesota, said there's no question on whether children will transmit the virus to others if they are in school.

    "There will be transmission," he said. "What we have to do is accept that now and include that in our plans" (Mandavilli, New York Times, 7/18; Sandler, Forbes, 7/18; Joon Park et al., Emerging Infectious Diseases, 7/16).

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