Majority of children have coronavirus antibodies: THL study

Ninety per cent of people under the age of 18 in the Uusimaa region had developed antibodies against coronavirus resulting either from vaccination or infection by the end of May 2022, according to a study conducted by the Finnish Institute for Health and Welfare (THL).

The presence of antibodies was examined at THL from serum samples taken from children aged 1–17 for other laboratory tests not related to the coronavirus disease at HUSLAB. The samples were selected randomly and processed at THL without any personal data.

The study used a test that measures the antibodies that detect coronavirus spike protein, developed as a result of both vaccination and infection.

The study also measured antibodies that can detect the nucleoprotein of the virus. The antibodies can only develop as a result of coronavirus infection. The antibodies can be measured from a blood sample several months after infection or vaccination.

In May, a total of 73 per cent of people aged 1–17 was found to have antibodies that indicate coronavirus infection.

“The study shows that coronavirus infections increased significantly in children in spring 2022. In December 2021, only 8 per cent of people under the age of 18 had antibodies that indicate a previous coronavirus infection, but the share had risen to 21 per cent in January, and as high as 73 per cent in May,” said Merit Melin, Research Manager at THL.

Antibodies that indicate infection were found 74 percent among 1–4-year-olds, 76 per cent among 5–11-year-olds and 68 percent among 12–17-year-olds.

According to the study, coronavirus infections also increased in children who received the vaccine during the spring.

“In December 2021, 78 per cent of the samples collected from 12–17-year-olds were found to contain antibodies developed as a result of vaccination, which corresponds to an estimate of the vaccination coverage in this age group in December based on the vaccination register. Based on the vaccination register, 80 per cent of those aged 12–17 and 25 per cent of those aged 5–11 had received at least one vaccine dose by May”, said Melin.

In total, antibodies developed as a result of a coronavirus infection or the combined effect of an infection and vaccination were found 76 percent among 1-4 year-olds,89 percent among 5-11-year-olds and 98 percent among 12-17-year-olds.

“A very large proportion of children and young people, especially those aged 12 or over, have developed hybrid immunity resulting from a combination of a coronavirus infection and vaccination. Hybrid immunity is stronger and more widely recognises different virus variants compared to protection developed as a result of an infection or vaccination alone”, Melin added.

A previous study by the THL found that in adults who had contracted coronavirus, just one vaccine dose produces strong immunity. Similarly, a coronavirus infection strengthens the protection previously developed through vaccination.

The new findings on children indicate that a significant proportion of adults in Finland also contracted coronavirus during the Omicron variant surge of last spring, which improves the immunity of the population as an addition to vaccinations.

A THL study previously estimated that, by March 2022, 27 per cent of adults living in the Helsinki and Uusimaa Hospital District had contracted coronavirus.

New research findings on the development of antibodies in adults will be completed later this autumn.