Scientists uncover why children suffer less severely from Covid

Immune systems better at spotting danger, University College London study finds

A girl of 5 is shown a syringe by a vaccination assistant before her first coronavirus vaccination in Germany. AP

Children’s immune systems are better at recognising the coronavirus as a threat, helping to explain why they suffer less severely from Covid-19, research has found.

Scientists said children’s airways produced strong antiviral proteins that stopped the virus in its tracks without having encountered it before.

Adults have a more adaptive immune system that is trained to recognise threats it has seen before – which is the principle behind vaccination.

But children have a stronger innate response that recognises dangers automatically, researchers said.

“The innate immune system of children is more flexible and better able to respond to new threats,” said Dr Masahiro Yoshida, one of the authors of the University College London study.

He described a very quick immune response in children that “helps to explain why they are less severely affected by Covid-19”.

Children can still spread the virus, and are recommended for vaccines in many countries. School-age children had the highest rates of infection in the UK in the week ending on December 17.

But rates of serious illness and death are very low – fewer than 100 people under 15 have died from Covid-19 in England. Scientists said this was not previously fully understood.

The UCL study explained that the airway proteins, known as interferons, give a signal to nearby cells to tighten their defences against an intruding virus.

Adults produce them too, but they were found to be stronger, more numerous and generated more quickly in children.

Interferons have been studied as a possible therapy for Covid-19, while researchers say a nasal swab could be used to measure the immune response in adults.

The findings are based on blood samples from 78 people, including children and adults infected by the virus.

This produced a data set of more than 650,000 individual cells that revealed dozens of cell types in the airways and blood – including some never previously described.

In addition, children were less prone to a dangerous effect in which the immune system works against the body by attacking infected cells. This is known as a cytotoxic response.

“Once the virus has spread to several areas of the body, organ damage can be caused by the immune system trying and failing to control the infection,” said Dr Marko Nikolic, another UCL study author.

“Our study shows that not only do children respond better initially, if the virus does enter the blood the cytotoxic response is less forceful.”

The research from UCL, the Wellcome Sanger Institute and their collaborators is published in Nature.