COVID-19, the respiratory illness caused by the infection with the novel coronavirus, is particularly dangerous for the elderly and individuals with chronic diseases. However, the disease seems to spare children, although they too can become infected and pass the virus to other people. In the most comprehensive study of its kind to date, scientists have confirmed that the virus is much less severe for children.

Most cases of children with COVID-19 are mild or moderate — some don’t show any sign of illness at all

Researchers at Shanghai Children’s Medical Center studied 2,143 cases of COVID-19 among children, from newborns to 18 years of age. The median age of the participants is 7 years.

More than 90% of the cases showed mild to moderate symptoms or were even asymptotic.

Mild cases, representing 52% of the cohort, were marked by the kind of symptoms one typically sees due to the common cold — fever, fatigue, sore throat, runny nose, and cough. Some mild cases also exhibited digestive symptoms such as nausea, vomiting, diarrhea, and abdominal pain.

Moderate cases — about 39% of all cases — progressed into pneumonia, which caused frequent fever and cough. There was no obvious shortness of breath in these cases.

Severe cases (5%) started off with early respiratory symptoms and were sometimes joined by gastrointestinal issues. After one week after the first symptoms appeared, the respiratory problems intensified.

Some of these severe cases progressed into those that required critical care (0.4%) due to acute respiratory problems or failure. In some situations, this led to heart failure or kidney injury.

About 4% of the children infected with SARS-CoV-2, the virus that causes COVID-19, didn’t show any symptoms at all. However, they still tested positive after doctors took nasal or throat swabs.

Only one fatality was registered among the over 2,000 participants — a 14-year-old boy with no further details concerning his condition, such as whether he suffered from any chronic disease known to complicate the disease (cancer, diabetes, high blood pressure, autoimmune disorders, and cardiovascular disease).

The findings are due to appear this week in the journal Pediatrics, but the results were made public earlier due to the urgency of the COVID-19 crisis.

They confirm what raw data suggested all along: children can get sick but it’s exceptional for them to die of the illness.

Young children might get infected just as often as adults — it’s just that they rarely show symptoms

Initially, scientists thought that the children are less likely to catch the disease in the first place. For instance, a study that followed 1,099 patients with COVID-19 from 552 hospitals in 30 Chinese provinces found very few infections among children — just 0.9% of confirmed cases were under the age of nine, while only 1.2% were between 10 and 19 years old. Of the nine children with COVID-19 in the study, just one developed severe symptoms.

In another recent analysis, researchers in the US and China analyzed more than 72,000 confirmed cases from China, finding that children under the age of 10 accounted for under 1% of all infections. There were 1,023 deaths in the sampled population, but not a single child was among them.

Children were similarly less affected compared to adults during the 2003 SARS outbreak, caused by a related coronavirus strain called SARS-CoV-1. Writing for The Scientist, journalist Anthony King says, “In Hong Kong, no one under the age of 24 years died, while more than 50 percent of patients over 65 succumbed to the infection. Globally, less than 10 percent of those diagnosed with SARS were children, and only 5 percent of them required intensive care.”

The real rate of infection among children might be much higher, though.

It seems like children may be just as likely to catch the novel coronavirus like any other age group — it’s just that they rarely get sick.

Justin Lessler, an infectious disease epidemiologist at Johns Hopkins Bloomberg School of Public Health, co-led a study with colleagues at the Harbin Institute of Technology in Shenzhen and the Shenzhen Center for Disease Control and Prevention in which they monitored 391 COVID-19 patients and 1,286 people who had come in contact with these patients.

When these contacts were tested, the researchers found that children aged 9 and younger were just as likely as other age groups to get infected (7-8% of the time).

Most of the children did not show any symptoms at all but they still carried varial loads that can infect other people.

So, although few children actually do get sick, they can be an important source of disease transmission, especially in the household. Many governments have shut down schools and kindergartens — in light of such findings, this has proven very wise so far.

Infants and toddlers are the most vulnerable to complications

That’s the good news. The bad news is that children and infants who do get sick seem to be particularly vulnerable to complications.

According to the results of the Pediatrics , 11% of the infants included in the study and 15% of children in the age group 1-5 were critical cases. These were the most vulnerable groups identified by the study.

The study didn’t answer one important question: why are most cases involving children with COVID-19 so mild compared to adults?

In their study, the authors share some opinions (which weren’t tested). It is possible that cell receptors that bind to the virus may be less sensitive in children. They also often catch the cold and other respiratory illnesses during the winter more frequently than adults, so the children might have built higher levels of antibodies to fight the infection.

Lastly, the study suggests that children likely play a major role in viral transmission. The results suggest that children have more symptoms that make them more contagious than the general population, such as runny nose. Their higher incidence of gastrointestinal issues also raises concerns that the virus may still linger in feces for weeks after the infection clears.

The main takeaway here is that children are largely protected against the most mortal effects of COVID-19 — although we’ll come to learn more about how the diseases affect children once the pandemic reaches its peak and more fringe cases appear. The findings also show that the children aren’t immune to the illness and the situation needs to be handled with care across all age groups.