The lining of children’s noses is better at inhibiting SARS-CoV-2 infections than those of the adults, which may explain why younger people had a lower infection rate and milder symptoms from earlier variants, according to a study.
Researchers from the University of Queensland (UQ) in Australia noted that the finding may be one of the reasons why children’s immune responses have so far proven more effective at avoiding and fighting COVID-19.
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However, the trend was markedly less pronounced in the case of the Omicron variant, they said.
“Children have a lower COVID-19 infection rate and milder symptoms than adults, but the reasons for this have been unknown,” said Kirsty Short from UQ.
“We have shown the lining of children’s noses has a more pro-inflammatory response to the ancestral SARS-CoV-2 than adult noses,” said Short. However, the study published in the journal PLOS Biology found that it is different when it comes to the Omicron variant.
The research team exposed the samples of nasal lining cells from 23 healthy children and 15 healthy adults to SARS-CoV-2.
The results showed that the virus replicated less efficiently in the children’s nasal cells, as well as a heightened antiviral response.
“It could be an adaptation to the increased threats of ‘foreign invaders’ such as viruses or bacteria observed in childhood,” Short said.
“It is also possible that increased exposure to these threats in childhood ‘trains’ the nasal lining in children to mount a stronger pro-inflammatory response,” she said. Alternatively, the researchers said, metabolic differences between children and adults could alter how virus-fighting genes express themselves.
They found that the Delta COVID-19 variant was significantly less likely to replicate in the nasal cells of children compared to adults.
However, the effect was markedly less in the case of the Omicron variant.
“Taken together, it shows children’s nasal lining supports lower infection and replication of ancestral SARS-CoV-2, but this may be changing as the virus evolves,” Short added.