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One mystery that scientists are still unpacking is why children are less impacted by the coronavirus pandemic than adults.

For the most part, children make up a very small percentage of the overall infected population; when they do have the disease, their symptoms tend to be mild.

"Not only are fewer children testing positive for COVID 19, but those that do test positive are likely to have milder cases," according to Priya Soni, a doctor and pediatric infectious disease specialist at Cedars-Sinai in Los Angeles.

That's not how most viruses have worked historically.

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"There is no other respiratory virus that we know, that affects adults so much more severely than infants," Soni said in a press release. "For example, when a child gets a viral infection there are usually more intense symptoms, accompanied by high fevers. In the case of COVID- 19, it's the adults who are getting the high fevers, having severe complications and even dying."

There are a few theories for why this might be. One is that since children have young immune systems, they don't develop the aggressive immune response known as a "cytokine storm" like adults do, which fosters lung damage and often harms adults.

Meanwhile, researchers at Boston Children's Hospital on Tuesday announced a new two-pronged study of children and young adults up to age 25 to examine a wide range of factors that may promote vulnerability in COVID-19.

"Our major goals are to understand why some children get very ill with COVID-19 and why most children aren't getting sick in the same numbers as adults," said Adrienne Randolph, a senior physician in Critical Care Medicine at Boston Children's and the study's principal investigator.

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"Based on what we know about other viruses, such as influenza, we would expect children to be the first to get sick and have more severe disease. If we can understand what protects kids, we may get clues as to why older people are so susceptible," Randolph said in a statement.

The study -- backed by $2.1 million in funding from the Centers for Disease Control and Prevention (CDC) -- will perform real-time surveillance at more than 35 U.S. children's hospitals to capture data on 800 patients hospitalized with COVID-19. In addition, it will enroll up to 400 of these patients for detailed, prospective observation and periodic collection of respiratory and blood samples.

As of Tuesday afternoon, the novel coronavirus had infected more than 1 million people in the U.S., and at least 57,266 people have died from the disease.