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COVID-19 coronavirus cases appeared to be less severe in children than adults, although infants and toddlers were more susceptible to the virus than older kids, according to a study done in Wuhan, China.

Among 2,143 pediatric cases of suspected or laboratory-confirmed coronavirus, most were mild (50.9%) or moderate (38.8%), and 5.9% were severe or critical (versus 18.5% for adults), reported Yuanyuan Dong, MPH, of Shanghai Jiao Tong University, and colleagues, in .

However, severe or critical cases were more common in younger children, and the prevalence decreased with children's age:

• <1 year: 10.6%
• 1-5 years: 7.3%
• 6-10 years: 4.2%
• 11-15 years: 4.1%
• ≥16 years: 3%

"Why most of the children's COVID-19 cases were less severe than adults' cases is puzzling," Dong and colleagues wrote, citing developing immune systems, increased rates of seasonal respiratory infections, or fewer chances of exposure as possible explanations.

The initial data on children's risk was scant although it has in small cohorts been shown to cause moderate to severe respiratory illness.

In the U.S., school officials have ranging from a couple of days to 5 weeks. Infectious disease experts have recommended a shutdown. China also closed its schools, although some are back in session, according to a .

In this study, 12.9% of children with confirmed cases were asymptomatic, a rate that "almost certainly understates the true rate of asymptomatic infection" and indicates children "may play a major role in community-based viral transmission," wrote Andrea T. Cruz, MD, MPH, of Baylor College of Medicine in Houston, and Steven L. Zeichner, MD, PhD, of the University of Virginia in Charlottesville, in an .

Community-transmission by children is also supported by evidence that suggests upper versus lower respiratory tract involvement is more common in kids, and that fecal shedding can persist for several weeks after diagnosis, increasing the likelihood of fecal-oral transmission for infants and children who are not yet toilet-trained, Cruz and Zeichner noted.

"Prolonged viral shedding in symptomatic individuals, combined with shedding in asymptomatic persons, would render contact tracing and other public health measures to mitigate spread less effective," they wrote.

Importantly, there are still certain subpopulations of children with an increased risk for more significant illness, consistent with data on non-COVID-19 coronaviruses, Cruz and Zeichner stated, including children with acute respiratory distress syndrome (ARDS), respiratory tract infections, underlying pulmonary pathology, and immunocompromising conditions, as well as children of a younger age.

Among symptomatic children in the study, 5% had dyspnea or hypoxemia and 0.6% progressed to ARDS or multiorgan system dysfunction, both of which are lower than what has been reported among adults, the researchers said.

Still, finding the attributable risk for severe disease from COVID-19 in children is "challenging to discern," Cruz and Zeichner stated.

Although prior studies have shown viral co-infections can occur in up to two-thirds of cases in children from whom coronaviruses are detected, the majority of the cases in this study were not virologically confirmed and testing for other viruses was not standardized, they noted.

Notably, children with clinical confirmation-only were more likely to have severe disease than children with virologic confirmation, "potentially because their symptoms were caused by other pathogens," Cruz and Zeichner commented.

Dong and colleagues examined Chinese Center for Disease Control and Prevention data on 731 laboratory-confirmed and 1,412 suspected cases reported as of February 8. Suspected cases involved exposed children who had signs of illness; lab tests with signs of infection; or abnormal chest X-rays, the authors reported.

Patients (mean age 7; 56.6% boys) were mostly from the Hubei province (45.9%), while 18.5% were from provinces bordering the Hubei province. There was no significant difference in disease severity between girls and boys, the authors reported.

One boy, age 14, from the Hubei province died in early February, they said.

Generally, pediatric cases increased "remarkably" between mid-January and early February, peaked around February 1 and then began declining, researchers reported. The median days in between illness onset and diagnosis was 2 days, and most cases were diagnosed within the first week of onset, they added.

Study limitations included the fact that some suspected cases may have been caused by other respiratory infections. Exposure history was also missing so that incubation periods could not be determined, the authors added.

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