PostedAugust 19, 2022, 07:01
CoronavirusChildren’s nasal cells protected them from early variants
The mucosa of the nose of the youngest is different from that of adults and has helped them to fight once morest Covid, but this was much less the case with Omicron.
The nasal mucosa of children defends once morest the coronavirus better than that of adults, at least until Omicron.
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From the start of the coronavirus pandemic, children were found to have far fewer symptoms than adults and when they did, they were mostly mild. It was also observed, at least during the waves of the ancestral virus and its first variants, that children under the age of 10 were significantly less contaminated than older people and were less likely to transmit the virus.
Several hypotheses have been put forward to explain these differences, in particular that the nostrils of children, the nose being the main entry point for the virus, contain fewer receptors to which the coronavirus clings than in adults. But this is not true in all cases.
A stronger antiviral response
Australian scientists have explored another way. They observed that if the nasal epithelial cells (i.e. the cells that line the lining of the nose, abbreviated NEC) of children are indeed different from those of adults, it is not only because of a different number of receptors of the coronavirus. Analysis of the nasal mucosa of children showed a stronger expression of genes associated with inflammatory and antiviral responses than in adults.
So the coronavirus would cause more inflammation in children? He should therefore have more serious symptoms of the disease. This is true when these inflammations occur in the lower airways (trachea, bronchi and lungs) where it can lead to respiratory distress. But when it happens in the upper respiratory tract (nose, sinuses, pharynx and larynx), this inflammation and increased production of interferons instead inhibits the replication of the coronavirus. In short, they act as an antiviral.
And this is what has been observed with the ancestral strain of the coronavirus, which replicates much less in the NECs of children than in those of adults. When the Delta variant appeared, it replicated more in the NECs of both adults and children, which explains why it was more contagious. But it was still noticeably less present among the youngest. Children were therefore even better protected than adults once morest Delta
Same amount of Omicron in children
When it was Omicron’s turn, it duplicated no more than Delta in the adults’ mucosa. Which assumes that his mutation did not give him an advantage in his replication. If it has yet proved to be even more contagious than Delta, it would rather be thanks to its ability to escape antibodies. But on the other hand, compared to the previous variants, there was no notable difference in the viral quantity of Omicron in the NECs of adults and children. The specificity of children’s mucosa therefore no longer protects them, or less effectively, once morest Omicron.
This corresponds to what has been observed, namely a much higher number of infections of children on Omicron than in previous waves. This may not be the only explanation, since it must also be taken into account that, while more and more adults were vaccinated, those under 12 were vaccinated much later and in weaker number.
Still, scientists from the University of Queensland, Australia, believe that their study, published in «PLOS Biology» provides “the first experimental evidence that the pediatric nasal epithelium may play an important role in reducing children’s susceptibility to ancestral SARS-CoV-2”. He may not be the only culprit, since children and adolescents also have more pre-existing coronavirus antibodies than adults, but he is undoubtedly part of the explanation for this better immunity in the early days. of the epidemic. With the evolution of the virus, it is difficult to say whether this will still be able to play a role in the future or not.
