Clinical manifestations of COVID-19 infection among children in mainland China generally have been less severe than those among adults, but children of all ages – and infants in particular – are vulnerable to infection, according to a review of 2,143 cases.

CDC/ Dr. Fred Murphy; Sylvia Whitfield

Further, infection patterns in the nationwide series of all pediatric patients reported to the Chinese Center for Disease Control and Prevention from Jan. 16 to Feb. 8, 2020, provide strong evidence of human-to-human transmission, Yuanyuan Dong, MPH, a research assistant at Shanghai Children’s Medical Center, Shanghai Jiao Tong University, China, and colleagues reported in Pediatrics.

Of the 2,143 patients included in the review, 57% were boys and the median age was 7 years; 34% had laboratory-confirmed infection and 67% had suspected infection. More than 90% had asymptomatic, mild, or moderate disease (4%, 51%, and 39%, respectively), and 46% were from Hubei Province, where the first cases were reported, the investigators found.

The median time from illness onset to diagnosis was 2 days, and there was a trend of rapid increase of disease at the early stage of the epidemic – with rapid spread from Hubei Province to surrounding provinces – followed by a gradual and steady decrease, they noted.

“The total number of pediatric patients increased remarkably between mid-January and early February, peaked around February 1, and then declined since early February 2020,” they wrote. The proportion of severe and critical cases was 11% for infants under 1 year of age, compared with 7% for those aged 1-5 years; 4% for those aged 6-10 years; 4% for those 11-15 years; and 3% for those 16 years and older.

As of Feb. 8, 2020, only one child in this group of study patients died and most cases of COVID-19 symptoms were mild. There were many fewer severe and critical cases among the children (6%), compared with those reported in adult patients in other studies (19%). “It suggests that, compared with adult patients, clinical manifestations of children’s COVID-19 may be less severe,” the investigators suggested.

“As most of these children were likely to expose themselves to family members and/or other children with COVID-19, it clearly indicates person-to-person transmission ” of novel coronavirus 2019, they said, adding that similar evidence of such transmission also has been reported from studies of adult patients.

The reasons for reduced severity in children versus adults remain unclear, but may be related to both exposure and host factors, Ms. Dong and associates said. “Children were usually well cared for at home and might have relatively [fewer] opportunities to expose themselves to pathogens and/or sick patients.”

The findings demonstrate a pediatric distribution that varied across time and space, with most cases concentrated in the Hubei province and surrounding areas. No significant gender-related difference in infection rates was observed, and although the median patient age was 7 years, the range was 1 day to 18 years, suggesting that “all ages at childhood were susceptible” to the virus, they added.

The declining number of cases over time further suggests that disease control measures implemented by the government were effective, and that cases will “continue to decline, and finally stop in the near future unless sustained human-to-human transmissions occur,” Ms. Dong and associates concluded.

In an accompanying editorial, Andrea T. Cruz, MD, of Baylor College of Medicine, Houston, and Steven L. Zeichner, MD, PhD, of the University of Virginia, Charlottesville, said the findings regarding reduced severity among children versus adults with novel coronavirus 2019 infection are consistent with data on non-COVID-19 coronavirus.

They pointed out that Ms. Dong and associates did find that 13% of virologically-confirmed cases had asymptomatic infection, “a rate that almost certainly understates the true rate of asymptomatic infection, since many asymptomatic children are unlikely to be tested.”

Of the symptomatic children, “5% had dyspnea or hypoxemia (a substantially lower percentage than what has been reported for adults) and 0.6% progressed to acute respiratory distress syndrome (ARDS) or multiorgan system dysfunction”; this also is at a lower rate than seen in adults, they said.

Very young children –infants or children in preschool – were more likely to have severe clinical manifestations than children who were older.

Thus, it appears that certain subpopulations of children are at increased risk for more significant COVID-19 illness: “younger age, underlying pulmonary pathology, and immunocompromising conditions,” Dr. Cruz and Dr. Zeichner suggested.

The two editorialists said the findings suggest children “may play a major role in community-based viral transmission.” Evidence suggests that children may have more upper respiratory tract involvement and that fecal shedding may occur for several weeks after diagnosis; this raises concerns about fecal-oral transmission, particularly for infants and children, and about viral replication in the gastrointestinal tract, they said. This has substantial implications for community spread in day care centers, schools, and in the home.

A great deal has been learned about COVID-19 in a short time, but there still is much to learn about the effect of the virus on children, the impact of children on viral spread, and about possible vertical transmission, they said.

“Widespread availability of testing will allow for us to more accurately describe the spectrum of illness and may result in adjustment of the apparent morbidity and mortality rate as fewer ill individuals are diagnosed,” Dr. Cruz and Dr. Zeichner wrote, adding that “rigorously gauging the impact of COVID-19 on children will be important to accurately model the pandemic and to ensure that appropriate resources are allocated to children requiring care.”

They noted that understanding differences in children versus adults with COVID-19 “can yield important insights into disease pathogenesis, informing management and the development of therapeutics.”

This study was partially supported by the Science and Technology Commission of Shanghai Municipality. The authors reported having no disclosures. Dr. Cruz and Dr. Zeichner are associate editors for Pediatrics. Dr. Cruz reported having no disclosures. Dr. Zeichner is an inventor of new technologies for the rapid production of vaccines, for which the University of Virginia has filed patent applications.

SOURCE: Dong Y et al. Pediatrics. 2020 Mar 16. doi: 10.1542/peds.2020-0702; Cruz A and Zeichner S. Pediatrics. 2020 Mar 16. doi: 10.1542/peds.2020-0834.