Objectives: To assess the longitudinal development of humoral immunity in children and adolescents during the COVID-19 pandemic, with a particular focus on how anti-spike IgG antibodies and neutralising response changed during the first Omicron peak (December 2021 to May 2022). Design: Prospective school-based study during the COVID-19 pandemic (June 2020 to July 2022) including five testing rounds with corresponding cross-sectional cohorts and a longitudinal cohort who participated in at least four rounds. Setting: 55 randomly selected schools in the Canton of Zurich, Switzerland. Participants: Between 1875 to 2500 children and adolescents per testing round and 751 in the longitudinal cohort. Main outcome measures: Development of SARS-CoV-2 seroprevalence, anti-spike IgG antibodies and neutralising antibody response over time, persistence of antibodies and variation of antibody levels in individuals only infected, vaccinated or with hybrid immunity during the early Omicron period. Results: By July 2022 96.9% (95% credible interval [CrI] 95.2 to 98.1%) of children and adolescents had anti-spike IgG antibodies against SARS-CoV-2. The substantial increase in seroprevalence during the first peak of the Omicron wave was largely driven by primary infections in mostly unvaccinated children under the age of 12 (28.4% [95% CrI 24.2 to 33.2%] in December 2021, to 95.7% [95% CrI 93.4 to 97.4%] in July 2022). This stands in contrast to adolescents aged 12 years and older (69.4% [95% CrI 64.0 to 75.4%] in December 2021 to 98.4% [95% CrI 97.3 to 99.2%] in July 2022), who were eligible for vaccination since June 2021. Children and adolescents with hybrid immunity or immunity from vaccination had high anti-spike IgG titres (median Mean Fluorescence Intensity (MFI) ratio of 136.2 [Inter Quartile Range [IQR]: 121.9 to 154.3] and 127.6 [IQR: 114.1 to 151.0]) and strong neutralising responses (e.g., anti-Omicron 98.9% [95% Confidence Interval [CI] 96.0 to 99.7%] and 81.6% [95% CI 74.9 to 86.9%]). Meanwhile, infected but unvaccinated children and adolescents had substantially lower anti-spike IgG titres (median MFI ratio of 54.8 [IQR: 22.8 to 89.8]) and neutralising responses (e.g., anti-Omicron 64.9% [95% CI 59.8 to 69.7%]). Conclusion: These findings show that the Omicron wave and the rollout of vaccines led to almost 100% seropositivity and boosted anti-spike IgG titres and neutralising capacity in children and adolescents. This was particularly driven by unvaccinated children (<12 years), who became seropositive due to the highly infectious Omicron variant. Nevertheless, during the entire study parents of only one adolescent reported hospital stay of less than 24 hours related to a possible acute infection.

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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

Almost 2 years into the pandemic and with vaccination of children significantly lagging behind adults, long-term pediatric humoral immune responses to SARS-CoV-2 are understudied. The C19.CHILD Hamburg (COVID-19 Child Health Investigation of Latent Disease) Study is a prospective cohort study designed to identify and follow up children and their household contacts infected in the early 2020 first wave of SARS-CoV-2. We screened 6113 children < 18 years by nasopharyngeal swab-PCR in a low-incidence setting after general lockdown, from May 11 to June 30, 2020. A total of 4657 participants underwent antibody testing. Positive tests were followed up by repeated PCR and serological testing of all household contacts over 6 months. In total, the study identified 67 seropositive children (1.44%); the median time after infection at first presentation was 83 days post-symptom onset (PSO). Follow-up of household contacts showed less than 100% seroprevalence in most families, with higher seroprevalence in families with adult index cases compared to pediatric index cases (OR 1.79, P = 0.047). Most importantly, children showed sustained seroconversion up to 9 months PSO, and serum antibody concentrations persistently surpassed adult levels (ratio serum IgG spike children vs. adults 90 days PSO 1.75, P < 0.001; 180 days 1.38, P = 0.01; 270 days 1.54, P = 0.001). In a low-incidence setting, SARS-CoV-2 infection and humoral immune response present distinct patterns in children including higher antibody levels, and lower seroprevalence in families with pediatric index cases. Children show long-term SARS-CoV-2 antibody responses. These findings are relevant to novel variants with increased disease burden in children, as well as for the planning of age-appropriate vaccination strategies. 

/pdf/long-term-antibody-response-to-sars-cov-2-in-children-11hlxw0j.pdf

Long-Term Antibody Response to SARS-CoV-2 in Children

In search for immunological correlates of protection against acute coronavirus disease 2019 (COVID-19) there is a need for high through-put assays for cell-mediated immunity (CMI) to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We established an interferon-γ release assay -based test for detection of CMI against SARS-CoV-2 spike (S) or nucleocapsid (NC) peptides. Blood samples obtained from 549 healthy or convalescent individuals were measured for interferon-γ (IFN-γ) production after peptide stimulation using a certified chemiluminescence immunoassay. Test performance was calculated applying cutoff values with the highest Youden indices in receiver-operating-characteristics curve analysis and compared to a commercially available serologic test. Potential confounders and clinical correlates were assessed for all test systems. 522 samples obtained from 378 convalescent in median 298 days after PCR-confirmed SARS-CoV-2 infection and 144 healthy control individuals were included in the final analysis. CMI testing had a sensitivity and specificity of up to 89% and 74% for S peptides and 89% and 91% for NC peptides, respectively. High white blood cell counts correlated negatively with IFN-γ responses but there was no CMI decay in samples obtained up to one year after recovery. Severe clinical symptoms at time of acute infection were associated with higher measures of adaptive immunity and reported hair loss at time of examination. This laboratory-developed test for CMI to SARS-CoV-2 NC peptides exhibits excellent test performance, is suitable for high through-put routine diagnostics, and should be evaluated for clinical outcome prediction in prospective pathogen re-exposure.

/pdf/performance-of-an-interferon-g-release-assay-based-test-for-24n5qzq3.pdf

Kathrin Cermann

Papers

Long-Term Antibody Response to SARS-CoV-2 in Children

Performance of an interferon-γ release assay-based test for cell-mediated immunity to SARS-CoV-2