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Are children infected with COVID-19 at a lower risk for severe complications and death?

"Yes, based on the information they have so far," said Dr. Lee Riley, a UC Berkeley professor and chair of the Division of Infectious Disease and Vaccinology. It's "unclear why."

The number of reported cases in children remains low. A study by the Chinese Center for Disease Control and Prevention looked at 44,672 confirmed cases and of those only 416 (less than 1%) were aged nine years or younger. No deaths were reported in this age group.

"The 10-to-19-year-old group also had a low rate," said Dr. Lee Atkinson-McEvoy, a pediatric doctor at UC San Francisco. "Even though there were some deaths, it was still low."

Another study using the same data from China honed in on nine children who tested positive for the new coronavirus, and of those, none had symptoms that were severe.

"Our understanding and our knowledge is evolving day-to-day and this is the experience in China where they have the largest number of cases," explained Atkinson-McEvoy. "They haven’t been able to look at whether it’s just age or other features [that's causing the lower risk]. We’re still recommending the common sense steps for kids to avoiding the spread of virus, and that's hand-washing, staying home when you’re sick, and avoiding locations where others may be sick."

Coronaviruses are among a group of viruses that cause the common cold, and there are seven known ones that can infect humans. Four of these (229E, HKU1, OC43 and NL63) are seasonal and typically cause mild respiratory infection – fever, cough, nasal congestion, and headache — according to Dr. Charles Chiu, a professor of laboratory medicine and infectious disease at UC San Francisco.

"The remaining three coronaviruses (MERS, SARS, COVID-19) are the result of recent zoonotic (animal-to-human) transmission events and although they are also associated with mild respiratory symptoms, infection can progress to cause severe, life-threatening pneumonia," Chiu shared in an email.

COVID-19 is the most recently discovered coronavirus and was unknown before the outbreak began in Wuhan, China in December 2019. To date, a vaccination or antiviral medication isn't available to treat it, according to the World Health Organization. People with serious illness should be hospitalized.

Dr. John Swartzberg, a professor of infectious disease at UC Berkeley, said he and his colleagues are looking at two hypothesis to explain why the Chinese study showed fewer complications in children. One is that the disease started in adults and has primarily been spreading among an older population.

The second is that children frequently get coronavirus infections — not this strain, but others. Swartzberg that coronaviruses cases account for about a third of all cases of the common cold and children are highly exposed to them in schools. "Would there be any cross-protection because kids are getting so many colds?" Swartzberg said. "That’s purely conjecture. There’s no data to support that at all, but it might explain this possible trend in children."

While children seem to be at a lower risk, available data suggests the elderly are more susceptible to complications and death.

The same Chinese study, which was not peer-reviewed by U.S. scientists, also looked at the disease in seniors. "The case fatality rates increased sharply with age from 0.2% to those under 40 to 14.8% to those above 80," said Chiu.

The symptoms of both flu and coronavirus overlap. "Death from coronavirus in patients with pneumonia is thought to be a combination of direct damage of the viral infection to the airways (bronchiolitis and/or pneumonia), an abnormal immune response (“cytokine storm”), and secondary bacterial infections," said Chiu. "This is similar to the way people die from flu."

With the flu, the elderly, very young, and those with compromised immune systems are at the highest risk for severe disease, while with COVID-19, it may be only the elderly and the immunocompromised with a significantly higher risk.

"I would say in general with most infections, the very young and the very immunocompromised tend to get a more severe case," said Atkinson-McEvoy. "That’s not what’s being seen with the current COVID epidemic. And it might be because the 30-to-79-year-olds are out in the world more and exposed to the virus more than children."

Amy Graff is a digital editor with SFGATE. Email her news tips and photos at agraff@sfgate.com.

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