From one study 44,672 people with a COVID-19 infection found that children under 10 years old made up less than 1 percent of cases – and none of the 1,023 deaths. “This is not like the flu,” says Akiko Iwasaki, professor of immunology at American Yale University. The flu is usually the hardest hit for young children and older people.
Why is that different with the new coronavirus SARS-CoV-2? That is still unclear. But it may be that children, as crazy as that may sound, are less at risk because their immune systems are not yet completely finished.
An obvious explanation for the low number of seriously ill children would be that children are less easily infected. However, that does not seem to be the case. A study even found that children are infected as easily as adults.
However, children who do become infected are less likely to develop and die of COVID-19 disease. Something similar happened before with SARS and MERS, two other serious diseases caused by coronaviruses. What protects our children then?
“Nobody has a good answer to that,” said Iwasaki. But she and other experts suspect it has to do with the unique way that children’s immune systems respond to these viruses.
A common complication of COVID-19, SARS and MERS in adults is acute respiratory distress syndrome (ARDS). In doing so, the immune system overreacts to the coronavirus and causes life-threatening damage to the lungs.
Fluid and immune cells then leak into the lungs and cause major problems, he says Chris van Tulleken, who holds a PhD in molecular virology from University College London. That immune system response is intended to attack the virus, but may ultimately block oxygen uptake in the lungs, Van Tulleken explains.
As children’s immune systems are still developing, they may not yet be able to respond to such a dangerous reaction – a so-called cytokine storm – if they develop COVID-19 or a similar disease. It emerged during the SARS outbreak two studies that children produce relatively few cytokines during inflammation. That may have protected their lungs from serious damage.
Read more about the new coronavirus and COVID-19 in our file.
However, that doesn’t explain why children’s immune systems respond differently to coronaviruses than they do to the flu. Perhaps the cytokine response differs per virus, Iwasaki says.
More evil than good
It may also be the case that children benefit from being little exposed to previous coronaviruses. Because adults have lived longer lives, they are more likely to have come into contact with other coronaviruses, which cause coughing fits and colds, for example. As a result, they already have antibodies against these milder viruses.
These existing antibodies may be a disadvantage rather than an advantage for adults, as they do not exactly fit the new coronavirus. “Sometimes mismatched antibodies do more harm than good,” says Wendy Barclay, who studies respiratory viruses such as the influenza virus at University College London.
Understanding why children are spared is not just a matter of scientific curiosity. “If we can somehow imitate children’s immune systems with therapy or medications, COVID-19 may also become no more than a mild infection in adults,” said Iwasaki.
And just because kids don’t get seriously ill doesn’t mean they don’t contribute to the spread of the virus. In addition, it appears that infected adults without symptoms can also spread the virus. The same could be true for children. Finding out if that is indeed the case is of great importance in fighting this pandemic.