Children aged 10 years and above can spread Covid-19 just as much as adults, study reveals
As countries such as the US debate whether and how to reopen schools amid the coronavirus pandemic, the evidence currently remains weak on how likely children are to transmit the virus to others. Researchers have now found that children between the ages of 10 and 19 can transmit Covid-19 within a household just as much as adults. While the risk was less for those below 10, it was not zero. The team from South Korea found that children younger than 10 can also spread the new coronavirus within their household but at rates that are much less.
When the initial patient in a household was younger than 10, the researchers found that 5.3% of household contacts tested positive for Covid-19. When the initial patient was between the ages of 10 and 19, 18.6% of contacts tested positive for the virus. A previous study had said that symptomatic (those who show symptoms) neonates, children, and teenagers shed infectious SARS-CoV-2, the virus that causes Covid-19, indicating that transmission from them is ‘plausible.’
In the current study, researchers analyzed reports for 59,073 contacts of 5,706 Covid-19 index patients reported in South Korea during January 20-March 27, 2020. An index patient is defined as the first identified laboratory-confirmed case or the first documented case in an investigation within a cluster. Of 10,592 household contacts, 11.8% had Covid-19. Of 48,481 non-household contacts, 1.9% had Covid-19, says the analysis published in the US Centers for Disease Control and Prevention journal Emerging Infectious Diseases.
“Of 10,592 household contacts, index patients of 3,417 (32.3%) were 20-29 years of age, followed by those 50-59 (19.3%) and 40-49 (16.5%) years of age. We detected Covid-19 in 11.8% of household contacts; rates were higher for contacts of children than adults. These risks largely reflected transmission in the middle of mitigation and therefore, might characterize transmission dynamics during school closure. Higher household than non-household detection might partly reflect transmission during social distancing, when family members largely stayed home except to perform essential tasks, possibly creating spread within the household,” write authors.
The analysis shows that household transmission of SARS-CoV-2 (the virus that causes Covid-19) was high if the index patient was 10-19 years of age. “We also found the highest Covid-19 rate (18.6%) for household contacts of school-aged children and the lowest (5.3%) for household contacts of children 0-9 years in the middle of school closure. Despite the closure of their schools, these children might have interacted with each other, although we do not have data to support that hypothesis,” says the team.
The authors acknowledge there are some limitations to the study such as the number of cases might have been underestimated because all asymptomatic patients might not have been identified. Besides, detected cases could have resulted from exposure outside the household. Further, they were unable to assess the true difference in transmissibility between household and non-household contacts because of the different testing thresholds.
However, despite the limitations, experts say the sample size was large and representative of most Covid-19 patients early during the outbreak in South Korea. They caution that even though the detection rate for contacts of preschool-aged children was lower, young children may show higher attack rates when the school closure ends, contributing to community transmission of Covid-19.
According to the authors, the role of household transmission of SARS-CoV-2 amid reopening of schools and loosening of social distancing underscores the need for a time-sensitive study to guide public health policy. The report says a contact survey in Wuhan and Shanghai, China, showed that school closure and social distancing significantly reduced the rate of coronavirus among contacts of school-aged children. In the case of seasonal flu epidemics, the highest secondary attack rate occurs among young children.
“Children who attend day-care or school also are at high risk for transmitting respiratory viruses to household members. The low detection rate for household contacts of preschool-aged children in South Korea might be attributable to social distancing during these periods. Yet, a recent report from Shenzhen, China, showed that the proportion of infected children increased during the outbreak from 2% to 13%, suggesting the importance of school closure. Further evidence, including serologic studies, is needed to evaluate the public health benefit of school closure as part of mitigation strategies,” suggests the team.
The researchers emphasize that contact tracing is especially important in light of upcoming future Covid-19 waves, for which social distancing and personal hygiene will remain the most viable options for prevention. Understanding the role of hygiene and infection control measures is critical to reducing household spread, and the role of masking within the home, especially if any family members are at high risk, needs to be studied, they add. “In the current mitigation strategy that includes physical distancing, optimizing the likelihood of reducing individual, family, and community disease is important. Implementation of public health recommendations, including hand and respiratory hygiene, should be encouraged to reduce transmission of SARS-CoV-2 within affected households,” the team recommends.