Since the onset of the coronavirus pandemic, children have largely been spared the worst health impacts of COVID-19. The same SARS-CoV-2 virus capable of killing a 50-year-old boy could leave a four-year-old boy unharmed.
Now, the US Centers for Disease Control and Prevention recommends that K-12 schools reopen this fall, saying that health risks should be weighed against staying home, disproportionately affecting low-income and minority children and those with disabilities who can rely more on programs like school lunch and after-school care. When those children can’t go to school, their grades drop, mental and physical health suffers, key moments for socializing are missed, and many are left behind with their routine vaccinations.
“Children suffer in different ways than adults,” says Megan Tschudy, a pediatrician at Johns Hopkins University School of Medicine.
However, scientists are still struggling to understand how the virus affects children and whether children can pass it on to their older caregivers. Overall, scientists don’t fully understand why multiple types of coronaviruses, including COVID-19 and its viral cousins SARS and MERS, have different levels of severity across all age ranges, says Rachel Graham, an epidemiologist at the University of Carolina. North Chapel Hill.
Graham, who first spoke to National Geographic in March about the effects of COVID-19 on children, says that our understanding of why the virus appears to be easy for children has not fundamentally advanced since then. Even with increasing evidence showing that more children are capable of contracting the virus than previously thought, experts can only theorize why children are largely spared the intense version of COVID-19 that affects so many. Adults.
It is also unclear how easily children can transmit the virus, both to each other and to adults. A robust study of nearly 65,000 children released by the South Korean Center for Disease Control last week showed that children in the 10-19 age range could spread COVID-19 within homes as effectively as grown ups.
According to the CDC, only 2 percent of domestic cases of COVID-19 have occurred in children under the age of 18, but the data collected by Bloomberg show that these rates can vary greatly by region. So far, 20 children under the age of five in the United States have died from COVID-19.
A small percentage of minors testing positive for COVID-19 develop a life-threatening condition called multisystemic inflammatory syndrome in children (MIS-C), and it is unclear whether the disease has other long-term consequences.
“It leaves lasting scarring in the lungs and can lead to more serious illnesses in the future,” says Graham. But, he adds, “those kinds of things will have to be studied in the longer term with children who have recovered from the disease.” And because young people have largely escaped such serious illnesses, “there has been much less research on them and much less evidence,” says Tschudy.
A large study is now underway in the United States to understand how COVID-19 infects children, even as parents and pediatricians are grappling with an upcoming school year scheduled to begin as infection rates continue to rise.
How well can they spread the disease?
“All things being equal, children are much more likely to transmit things,” says Graham, referring to the way children in particular tend to interact with each other and touch all kinds of objects and body parts. However, he notes that there is not enough data to show that they do transmit the virus along with adults.
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While the South Korean study showed that children over the age of 10 transmitted the virus effectively, much younger children were 72 percent less likely to transmit the disease to adults.
However, it is not ruled out that a child under the age of 10 can transmit the virus. One study found that very young children, including babies, left traces of the virus, although it is unclear how infectious these remains were. But another study tracked a COVID-19-positive nine-year-old boy who visited three schools without transmitting the virus. The way children are managed seems to play an important role in transmission. Day care centers that remained open during the pandemic have had a variety of experiences, from large outbreaks in camps to infection-free day care centers.
A theory as to why children may be less likely to transmit the disease to others has to do with the fact that COVID-19 spreads mainly through the drops you exhale, and children can exhale with less force and closer to the ground.
“If you have children, you know they can yell quite loudly, but that may not translate to further extension,” says Barnett, considering that a child’s loud tone lacks the full force of an adult’s cough or sneeze.
“Although they congregate, they are not grouped together in things like the New York subway, bars or sporting events in the same way,” he says.
And where a sick adult is likely to commute to a shared office daily, parents are often careful to keep their sick children at home.
Ultimately, Barnett notes, experts can only offer theories.
“One thing that would make this much easier to understand is the results of contact tracing,” says Graham. “That would give a much better idea of how many people come into contact with each other.”
Why don’t children under the age of 10 seem so sick?
“At the start of the pandemic, there was so little that was known to all ages,” says Tschudy. “All ages were supposed to be affected equally, and there was a lot of preparation.” The early closure of school, he says, may have played a role in protecting children from the virus.
The tests were also limited to people showing visible signs of possible COVID-19 infection, and Tschudy says that infected and asymptomatic children likely went unnoticed.
A prevailing theory for children under the age of 10 doesn’t seem to get as sick with an enzyme called ACE2. When SARS-CoV-2 enters the body, the pointy proteins that surround the virus attach to ACE2 like a key that fits in a lock.
“One of the theories is that children have [ACE2] receptors for this virus more in the nose [and] in the upper respiratory system than in the lungs, and adults have these receptors in the lungs, “says Elizabeth Barnett, chief of pediatric infectious diseases at Boston Medical Center and professor of pediatrics at Boston University School of Medicine .
The production of more ACE2 receptors in the lungs is a theory as to why adults have more serious COVID-19 infections, he notes.
A study of 305 people ages 4 to 60 found that ACE2 enzymes were less active in children younger than 10 years.
The more resilient and adaptive immune systems can also help young children defend themselves against the disease, says Alvaro Moreira, a neonatologist at the University of Texas Health Sciences Center at San Antonio. It describes two attack methods used by a person’s immune system: “one that requires no memory and one that does.”
Over time, as we age and expose ourselves to bacteria and viruses, our bodies’ immune systems create cells that remember specific viruses and can then attack them more efficiently. The body of a child who is still building this memory depends on the other method of attack by the immune system.
“That is the innate immune system,” says Moreira. “And we know that children are less likely to have an exaggerated innate response.”
When the innate immune system attacks, immune cells indiscriminately take pathogens that enter the body. Also during this attack, the body releases molecules called cytokines, which help cells communicate with each other. When too many cytokines are released by the immune system, they attack healthy tissue. Some of the sickest adult COVID-19 patients have died from these so-called “cytokine storms.”
Tschudy says that children tend to have lower levels of cytokines to protect them from such storms, possibly because “young children are exposed to new infections all the time, so when their bodies are exposed to a new virus like COVID-19 “Your immune systems can be prepared to respond strong enough to fight the virus and not harm your bodies.”
Some children face greater risks
While a child’s immune system may appear biologically ready to avoid COVID-19, not all children are affected equally.
“The vast majority of children with severe COVID tend to have other risk factors,” says Philip Zachariah, a pediatric infectious disease specialist at Columbia University and an epidemiologist at Morgan Stanley Presbyterian Children’s Hospital in New York.
In a study he published in early June, Zachariah reviewed the cases of 50 children admitted for COVID-19. All but one child recovered. Obesity in children older than two years was associated with more severe manifestations of the disease, although Zachariah emphasizes that this may simply reflect the neighborhoods served by the New York Presbyterian.
“I think the data is generally consistent with the fact that low-income children and racial minorities are more infected,” he says.
Overall, he says, even young children who get sick seem to be more likely to recover than sick adults. And the same ways that adults stay safe – social estrangement, wearing masks, and handwashing – will ultimately help children contain the virus.
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