Coronavirus: Children produce weaker immune response, study shows

Children infected with coronavirus generate a weaker immunological response than adults but go on to clear their infection much quicker, a new study has shown.

Scientists at Columbia University in New York found that children produce weaker antibodies and fewer types of them, suggesting they are more efficient in tackling Sars-CoV-2 - the virus that causes Covid-19.

The speed in which children overcome coronavirus could also help explain why they are less likely to transmit it to others.

Professor Donna Farber, an immunologist at Columbia who co-authored the study, said: "In kids, the infectious course is much shorter and probably not as disseminated as in adults.

“Kids may clear this virus more efficiently than adults and they may not need a strong antibody immune response to get rid of it."

The study, published in Nature Immunology, reveals a stark contrast with adults, who have been known to generate strong immunological responses that can culminate in severe disease or even death.

Among the 47 children in the study, 16 had multi-system inflammatory syndrome (MIS-C). The remaining 31 did not have the rare condition, with half of this second group showing no Covid symptoms at all.

The 32 adults in the study ranged from severely affected patients admitted to the hospital to those with milder disease who recovered at home.

Both groups of children produced the same antibody profile, the study found, which differed from that of the adults.

The children's antibodies had the least neutralising activity, while the sickest adults had the highest activity levels. Prof Farber said this likely reflects the amount of time the virus was present in these patients.

"There is a connection between the magnitude of your immune response and the magnitude of the infection,” she said.

“The more severe the infection, the more robust the immune response, because you need to have more immune cells and immune reactions to clear a higher dose of a pathogen."

The children in the study also made primarily one type of antibody - called IgG - that recognises the ‘spike’ protein on the surface of Sars-CoV-2.

In contrast, the adults produced several types of antibodies, which were more powerful at neutralising the virus.

The findings of the research could also have implications for many antibody tests, including those made by Abbott and Roche, which are designed to detect the N antibodies that are largely absent in children.

Experts have said that the varied immune response could be explained by the fact the virus behaves differently in children and adults.

Eleanor Riley, a professor of immunology and infectious disease at the University of Edinburgh, said: “One hypothesis is that the receptor protein in the respiratory tract that binds Sars-CoV-2 (and allows it to invade the cells of the lung) is expressed at a lower level in children than in adults.

“As we age, more of this receptor protein is expressed and our lungs become vulnerable to infection. This may be important as tissue damage and inflammation provide a strong stimulus for the immune response, leading to more antibody being produced and more diverse the types of antibodies being produced.”

Experts have urged some caution in interpreting the results because they represent samples taken from people at a single point in time, while the type of antibodies produced by the body varies over the course of an infection.

The study comes as separate research showed that the antibody levels can fall by half in less than 90 days, and do so at a faster rate in younger adults.

The ongoing study of staff at Oxford University Hospitals NHS Foundation Trust (OUH) also recalled that virus antibodies last longer in people who have had symptoms and fade quicker in asymptomatic people.

By measuring antibody responses in the same healthcare workers for up to six months, researchers followed what happens to antibody levels over time and how this varied between different people.

They found that in this cohort of working-age healthcare workers, antibody levels rose to a peak at 24 days after the first positive Covid-19 test. They then began to fall.

Those tested had lost their positive antibody result after an average of 137 days, the study suggests.