Last Friday, high school junior Jameela Barber called her teacher in Dallas County, Texas, to apologize for neglecting to turn in her school work.
Her school's principal, Eleanor Webb, said Barber told her teacher she hadn't been feeling well.
"She said, 'As soon as I feel better, because I'm feeling really, really sick, I'm going to turn in my missed assignments,'" Webb told NBC affiliate station KXAS.
The next day, Webb said, Barber died of complications from COVID-19. She was 17.
Barber's case is rare; only a handful of pediatric deaths related to the coronavirus have been reported in the United States. However, the exact numbers for kids are hard to pin down: the Centers for Disease Control and Prevention told NBC News that it does not track COVID-19 deaths in children under age 18 the way it does for the flu.
Early data on pediatric COVID-19 cases suggested that, for the vast majority of children, the illness is relatively mild.
Recently, however, reports of potential serious complications specific to children have begun to emerge in the U.S. and Europe: A handful of kids have developed dangerous inflammation around the heart and other organs. It's similar to a rare condition called Kawasaki disease, which causes swelling of the coronary arteries, primarily in children.
Efforts to gather data on how the virus affects children are in their early stages. The Pediatric Infectious Diseases Transplant Network, in coordination with St. Jude Children's Research Hospital and other major children's hospitals across the country, have just begun to collect data on kids diagnosed with COVID-19.
It's unclear why most kids appear to be spared. It could be that kids tend not to have the same chronic health problems, such as high blood pressure or Type 2 diabetes, found in the most serious COVID-19 cases in adults.
It could also be that children's immune systems don't react to this coronavirus infection with the same hyper-inflammatory response that's been documented in adults.
"This is very perplexing," Dr. Adrienne Randolph, a senior critical care physician at Boston Children’s Hospital, said. "What is it about their immune system and their immune reaction to this virus that is making it so they're really not getting sick?"
Randolph is leading a nationwide research project that aims to figure out why the virus acts differently in kids, and why a few, like Barber, have more serious and even deadly outcomes. The goal is to enroll 800 children and young adults up through age 25.
A large amount of data focusing on COVID-19 risks among young people is important, Randolph said, "because when a vaccine does become available, it's probably not going to be available for everybody right away."
That is, a vaccine would likely be prioritized for those most at risk for coronavirus complications.
'A new syndrome'
The handful of children who have developed the Kawasaki-like complication reflect "a new syndrome," said Dr. Jane Burns, director of the Kawasaki Disease Research Center at the University of California, San Diego.
"The way this is affecting the heart is completely different than what we usually see in Kawasaki disease," Burns said. "This is new because this is primarily the heart muscle that is failing," adding that it appears the immune system is attacking the heart, as opposed to the coronary arteries.
It's unclear how many children may have this condition. Doctors at the Columbia University Medical Center in New York reported treating three such cases in children ranging in age from 6 months to 8 years.
"What we have been seeing [is] there are some children who may have an inflammation of the blood vessels and are developing a toxic shock-like syndrome," New York Health Commissioner Dr. Howard Zucker said during a news conference Thursday.
Download the NBC News app for full coverage of the coronavirus outbreak
But it may be too early to link this new type of inflammatory reaction to COVID-19, because only some of the patients have tested positive for the coronavirus infection. A few have tested negative, though they had been exposed to infected family members.
The development has perplexed physicians, who have scheduled a call with experts from around the globe this weekend to share information about cases.
"We are scrambling to put together a unified case definition," Burns said.
The World Health Organization is also now "urgently" investigating the potential link between this new problem and COVID-19.
Ultimately, COVID-19 remains uncommon in children; just 2 percent of kids tested for the coronavirus in the U.S. are positive. By far, most COVID-19 cases — especially the most severe cases — have been among adults.
Pediatric infectious disease specialists stress complications from the coronavirus are rare in children, a trend that's been observed in other countries, as well.
"We have data from China, we have data from Italy, and other parts of Europe, as well as now some preliminary data in the United States" that most pediatric cases appear to range from asymptomatic to mild symptoms, Randolph said.
People over age 65 tend to have significantly higher rates of complications and mortality.
Dr. Buddy Creech, director of the Vanderbilt Vaccine Research Program at Vanderbilt University Medical Center in Nashville, has noted the same thing.
Symptoms in kids "seem to consistently be much milder than the adults," Creech said. And there's a growing theory that fewer symptoms for a shorter amount of time might indicate kids may not be very good at spreading the virus.
"It's tempting to hypothesize," Creech said, stressing that the theory has not been proven.
But, he added, "it would be interesting to at least consider the possibility that kids having milder symptoms and shorter illnesses might actually have fewer days of positive virus that they're shedding from their nose or their throat."