In a recent study posted to the medRxiv* preprint server, researchers discussed the presence of persistent humoral immunity among children and adolescents during the coronavirus disease 2019 (COVID-19) pandemic.

Study: Persistent humoral immunity in children and adolescents throughout the COVID-19 pandemic (June 2020 to July 2022): a prospective school-based cohort study (Ciao Corona) in Switzerland. Image Credit: oronaBorealis Studio/Shutterstock.com

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Background

Tracking seroprevalence and alterations in humoral immunity in children and adolescent individuals against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is crucial for understanding the pandemic’s progression and informing public health measures, such as vaccination and school prevention strategies.

Multiple serological studies were carried out to identify SARS-CoV-2 infections among children and adolescents and to assess the prevalence of antibodies at various stages of the pandemic.

However, limited longitudinal studies have been conducted to assess the development and persistence of antibodies over time in children and adolescents, resulting in a lack of knowledge about their humoral immunity.

About the study

In the present study, researchers explored the progress of humoral immunity among children and adolescents over time during the COVID-19 pandemic.

Primary schools situated in the canton of Zurich were randomly selected, and their corresponding geographically closest secondary schools were invited. Almost 55 schools out of 156 invited schools, including public and private schools, agreed to participate.

The study randomly selected classes and divided them into three strata based on school level: grades one to two for lower school, grades four to five for middle school, and grades seven to nine for upper school.

Five rounds of venous blood specimens were collected. The testing rounds were conducted at different times, termed T1 in June/July 2020, T2 in October/November 2020, T3 in March/April 2021, T4 in November/December 2021, and T5 in June/July 2022. Venous blood samples were collected from children and adolescents in schools during all five testing rounds.

The study collected data on participants’ sociodemographic features, chronic conditions, and COVID-19 vaccination status using online questionnaires at enrolment and every three to six months throughout the study.

Results

The number of children and adolescents tested ranged from 1,876 to 2,500 during each testing round from June 2020 to July 2022. Three children and adolescents who tested positive for antibodies were hospitalized for less than 24 hours during the study period. One hospitalization may have been due to acute COVID-19.

The seroprevalence rate exhibited a significant increase between T4 and T5, rising from 46.4% to 96.9% in the entire study population. Among unvaccinated children and adolescents, the rate increased from 31.3% to 95.8%. The vaccination rate for children and adolescents increased from 25.3% at T4 to 43.4% at T5.

Seroprevalence increased more significantly in children under 12 years old, rising from 28.4% to 95.7% between T4 and T5, compared to adolescents aged 12 and above, whose seroprevalence increased from 69.4% to 98.4%.

The team also found that children and adolescents who had hybrid immunity and were only vaccinated had high titer levels at either T4 or T5. On the other hand, unvaccinated children and adolescents who were infected had considerably lower titers.

Notably, on average, all groups experienced an increase in titers from T4 to T5. Children and adolescents who were either infected or had no antibodies at T4 and were vaccinated with the first dose between T4 and T5 showed the greatest increase in titers.

Moreover, children and adolescents with previous seronegative samples who had a history of SARS-CoV-2 infection showed the smallest increase and lowest titers in T4 and T5.

The neutralizing activity showed an increase in all groups from T4 to T5. Participants with hybrid immunity and those who received only vaccination had a comparable proportionally higher neutralizing response, while infected participants had a lower response.

At T4, infected children and adolescents had a higher neutralizing response at T5 in comparison to seronegative children and adolescents. In general, the highest neutralizing response was observed against anti-SARS-CoV-2 wildtype, followed by anti-SARS-CoV-2 Delta and anti-SARS-CoV-2 Omicron.

However, in children and adolescents who were newly infected between T4 to T5, anti-Omicron showed the highest neutralizing response, followed by anti-Delta and anti-wildtype.

Conclusion

The study findings emphasized the significance of serological studies as a means of monitoring COVID-19 and the emergence of humoral immunity in young individuals.

The SARS-CoV-2 Omicron variant wave and vaccine distribution resulted in nearly 100% seropositivity among children and adolescents, leading to increased seroprevalence as well as anti-spike immunoglobulin (Ig)-G antibody titers, as well as improved neutralizing capacity.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.