THL study: The majority of children have coronavirus antibodies as a result of infection or vaccination
According to a study conducted by the Finnish Institute for Health and Welfare (THL), 90 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.
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.
Increase in children’s coronavirus infections during the spring
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,” says Merit Melin, Research Manager at THL.
Antibodies that indicate infection were found in different age groups as follows:
- 1–4-year-olds: 74 per cent.
- 5–11-year-olds: 76 per cent.
- 12–17-year-olds: 68 per cent.
Hybrid immunity developed in many children as a combined effect of infection and vaccination
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”, says Melin.
In total, antibodies developed as a result of a coronavirus infection or the combined effect of an infection and vaccination were found in different age groups in May as follows:
- 1–4-year-olds: 76 per cent.
- 5–11-year-olds: 89 per cent.
- 12–17-year-olds: 98 per cent.
“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 explains.
A previous study by the Finnish Institute for Health and Welfare (Ref. 1) 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.
Many had coronavirus during the Omicron surge in spring 2022
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 (Ref. 2) 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.
Further information
Serological population survey of the coronavirus epidemic
Merit Melin
Research Manager
THL
[email protected]
