Scientists currently do not know why children are less likely to develop severe symptoms (persistent high fever, severe cough, shortness of breath, and extreme body ache) if infected with SARS-CoV-2, the virus that causes COVID-19. The Centers for Disease Control and Prevention (CDC) noted that while some children and infants have been sick with COVID-19, adults make up most of the known cases to date .

Initial data from more than 72,000 cases of COVID-19 in Wuhan, China showed that just 2% of the infected cases were under the age of 19 . Similarly, a February report from the World Health Organization’s (WHO) mission to China showed that those under 18 accounted for only 2.4% of the infected. Out of those infected young people, 2.5% developed severe disease and 0.2% developed critical disease.

While we don’t know why children are less likely to show severe symptoms, researchers are trying to understand how children experience COVID-19. They see some distinctions in symptom presentation between children and adults who are infected with SARS-CoV-2. A retrospective analysis of 366 hospitalized children in Wuhan, China, from January 7 to January 15, 2020 found SARS-CoV-2 in 6 patients (1.6%). All six children experienced high fever (>39°C, > 102.2°F ) and cough, and four of the six children had pneumonia, as assessed by x-ray. However, another analysis of 10 Chinese children infected with SARS-CoV-2 found their chest X-rays lacked definite signs of pneumonia, one defining feature of infection in adults.

A study in the journal Pediatrics of more than 2,100 children in China found that children of all ages were vulnerable to COVID-19, regardless of biological sex, though the vast majority experienced mild symptoms, and some experienced none at all. This is different from what we are seeing emerge from COVID-19 infection rates in adults, as scientists have begun to see more men than women becoming infected, and a higher proportion of infected men dying in Italy and China.

Data on COVID-19 cases among U.S children was recently published by the CDC in a Morbidity and Mortality Weekly Report (MMWR). As of April 2, 2020 149,082 cases of COVID-19 were reported for which age was known, and 2,572 (1.7%) occurred in children under 18 years. For reference, children under the age of 18 account for 22% of the U.S. population. Reported symptoms of COVID-19 among children in the US are a lot like those of children in other countries in that pediatric patients reported fever, cough, and shortness of breath, though less frequently than adults (73% of children reported symptoms compared to 93% of adults 18-64 reporting at least one of these symptoms). Data on child’s biological sex was known for 2,490 pediatric cases and 1,408 (57%) COVID-19 cases occurred in males, a finding that has been seen in adults as well. Reasons for any potential sex differences in COVID-19 cases remains unknown and requires further research.