SARS-CoV-2 Seroprevalence in Preschool and School-Age Children—Population Screening Findings From January 2020 to June 2022

Abstract

Background: The SARS-CoV-2 pandemic is ongoing in Germany. Children and adolescents are increasingly being infected, and many cases presumably remain undetected and unreported. Sero-epidemiological studies can help estimate the true number of infections.

Methods: From January 2020 to June 2022, 59 786 persons aged 1-17 years were tested for SARS-CoV-2 antibodies as part of a screening program for presymptomatic type 1 diabetes in the German federal state of Bavaria (the Fr1da study).

Results: In June 2022, the seroprevalence in the overall population was 73.5%. The seroprevalence was significantly higher in school-age children (from 5 to 10 years of age) than in preschool children (ages 1-4): 84.4% vs. 66.6%, p <0.001. In contrast, in November 2021, before the appearance of the omicron variant, the overall seroprevalence was 14.7% (16.2% of school-age children, 13.0% of preschool children, p = 0.06). In the overall collective, seroprevalence increased fivefold from the fall of 2021 to June 2022 (by a factor of 5.2 in school-age children and 5.1 in preschool children). Similar seroprevalences, with smaller case numbers, were observed in June 2022 in the corresponding Fr1da studies in Saxony and Northern Germany: 87.8% and 76.7%, respectively.

Conclusion: Monthly case counts reveal a substantial rise in SARS-CoV-2-infections among children and adolescents from late 2021 to mid-2022. The high percentage of preschool and school-age children who have been infected with SARS-CoV-2, in a population that has low vaccination coverage, should be taken into account in the development of health policies.

Figure 1

Monthly SARS-CoV-2 seroprevalence (proportion of tested samples that were antibody-positive) in children and adolescents aged 1–17 years. a) Fr1da study in Bavaria from January 2020 to June 2022. b) Fr1da study in Saxony from September 2021 to June 2022. c) Fr1da study in northern Germany (Lower Saxony and Hamburg) from August 2021 to June 2022. N is the total number of children and adolescents tested in each separate period. The blue columns show the prevalence of recovered or recovered and vaccinated persons among the participants, while the beige columns (from January 2022, when vaccination of children aged 5–11 years was recommended in Germany) depict the prevalence of vaccinated persons without prior infection or with infection at a much earlier time, based on their antibody profile. SARS-CoV-2, Severe acute respiratory syndrome coronavirus 2

Figure 2

Distribution of the SARS-CoV-2 RBD immunoglobulin-G antibody titers of the positive samples (> 25 BAU) in the Fr1da study in Bavaria from April 2020 to June 2022. Box plots (median and IQR) with lines for measurements within 1.5 IQR and dots for values exceeding 1.5 IQR. N is the number of RBD-positive children and adolescents (age 1–17 years) in each separate period (see cluster analysis in eFigure 2). BAU, Binding antibody units; IQR, interquartile range; RBD, receptor binding domain; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2

eFIGURE 1

SARS-CoV-2 RBD antibody titer in recovered and vaccinated children and adolescents of the Fr1da study in Bavaria. The figure shows the RBD antibody titers (> 25 BAU) of recovered persons without vaccination (all RBD-positive and NP-positive cases between January 2020 and July 2021) and of vaccinated persons with or without prior infection (confirmed vaccination, RBD positive and NP positive or negative). Box plots (median and IQR) with lines for measurements within 1.5 IQR. All group differences are significant (Wilcoxon test, p < 0.001). BAU, Binding antibody units; IQR, interquartile range; NP, nucleocapsid protein; RBD, receptor binding domain; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2

eFigure 2

Distribution of the SARS-CoV-2 RBD immunoglobulin-G antibody titers in the positive samples (> 25 BAU) per pediatrician‘s office in the Fr1da study in Bavaria from April 2020 to June 2022. The median antibody titers from each pediatrician‘s office are expressed as box plots (median and IQR) with lines for measurements within 1.5 IQR and dots for values exceeding 1.5 IQR. BAU, Binding antibody units; IQR, interquartile range; RBD, receptor binding domain; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2