Coronavirus: Children at similar risk of infection as adults but less likely to have severe symptoms
The rapid spread of the new coronavirus has sparked alarm worldwide and many questions are yet to be answered. A key piece in the puzzle scientists have been trying to solve is whether children are susceptible to COVID-19. And now experts finally have some answers.
Children are just as likely to get infected with the new coronavirus as adults, but less likely to have severe symptoms, according to one of the most detailed studies to date by US and Chinese researchers.
The team found that children under 10, who are exposed to the virus, are as susceptible to get infected as adults and it might be the first such study to provide clear evidence on the same.
The team includes experts from Johns Hopkins Bloomberg School of Public Health, Baltimore, US; Shenzhen Center for Disease Control and Prevention, Shenzhen, China; Harbin Institute of Technology at Shenzhen, Shenzhen, China and Peng Cheng Laboratory, Shenzhen, China. They have posted their findings to the medRxiv preprint server.
“Hopefully this new info helps to inform the public health response,” tweeted study author Justin Lessler from Johns Hopkins Bloomberg School of Public Health.
“An important new preprint finds that children are just as likely as adults to be infected. This is a key piece of data that may support school closures as an effective intervention,” tweeted Caitlin Rivers, assistant professor at Johns Hopkins Center for Health Security, who was not involved in the study.
The researchers analyzed data collected by the Shenzhen Center for Disease Control and Prevention (Shenzhen CDC) on 391 confirmed cases (between January 14, 2020 and February 12, 2020) of COVID-19 and 1,286 of their close contacts (cases before February 9) to characterize key aspects of its epidemiology outside of Hubei province.
The analysis is unique as it also looked at close contacts. Those in the contact-based group were tested for COVID-19 infection regardless of symptoms.
Close contacts in the study were defined as those who lived in the same apartment, shared a meal, traveled or socially interacted with an index case during the period starting two days before symptom onset. Casual contacts (for example, other clinic patients) and some close contacts (for example, nurses) who wore a mask during exposure were not included in this group.
The study says that 95% of close contacts were followed 12 days or longer. Ninety-eight tested positive for COVID-19 infection and one had presumptive infection. Attack rates were similar across infectee age categories, though there is some indication of elevated attack rates in older age groups, shows analysis.
Notably, the analysis shows that the rate of infection in children under 10 - 7.4% - was similar to the population average, which was 7.9%. An estimated 95% of cases are expected to develop symptoms within 14.3 days of their infector.
“Our data on cases as well as their infected and uninfected close contacts provide key insights into SARS-CoV-2 epidemiology. We show that children are at similar risk of infection as the general population, though less likely to have severe symptoms; hence should be considered in analyses of transmission and control,” says the team.
Overall, 1,286 close contacts were identified for cases testing positive for COVID-19, with 83% (244/292) of cases having at least one close contact. The team found that close to one in six contacts were infected.
“In Shenzhen, COVID-19 transmission is most likely between very close contacts, such as individuals sharing a household,” say researchers.
They explain, “Household contacts and those traveling with a case where at a higher risk of infection than other close contacts. The household secondary attack rate was 15%, and children were as likely to be infected as adults. The observed reproductive number was 0.4, with a mean serial interval of 6.3 days.”
As of February 22, 2020, final clinical outcomes were known for 228 of the 391 cases in the data with three having died and 225 recovered. Severe symptoms were associated with being male and there was a general trend of “increasing probability of severe symptoms” with age.
“Based on 228 cases with known outcomes, we estimate that the median time to recovery is 32 days in 50-59 year olds and is estimated to be significantly shorter in younger adults (for example, 27 days in 20-29 year olds) and significantly longer in older groups (for example, 36 days in those aged 70 or older),” says the study.
Some questions remain. For example, it is not yet clear whether children are important in transmitting the new coronavirus as they are with the influenza virus.
So far, there has been very limited information on how COVID-19 is impacting children. Previous studies have suggested that children are less likely to get affected by COVID-19. However, before this study, it was not clear whether children are less likely to be infected in the first place or their bodies are better equipped to fight the virus.
One of the largest studies which looked at a total of 72,314 patient records and 44,672 (61.8%) confirmed cases had said that the 80 and 80-plus age group had the highest case fatality rate of all age groups at 14.8%.
During a media briefing on February 17, World Health Organization (WHO) Director-general Dr Tedros Adhanom Ghebreyesus had said that “we see relatively few cases among children” and “more research is needed to understand why.”
A previous analysis had said that infants are at risk of contracting disease despite being largely spared.
The study had suggested that this may be due to a lower risk of exposure or incomplete identification due to mild or asymptomatic disease, rather than resistance to infection. The study was based on an analysis of nine infants who were infected with COVID-19 and were hospitalized in China between December 2019 and February 6, 2020.