Highlights: 10• A publicly available SARS-CoV-2 RT-PCR assay was adapted and evaluated on the open mode 11 of the NeuMoDx 96 system (Qiagen) 12• The assay showed comparable analytical and clinical performance to the reference assay 13• Fast turn-around times (80 minutes) and random-access workflow of the system makes the 14 assay well suited for urgent clinical samples. 15

Background: Molecular testing for SARS-CoV-2 continues to suffer from delays and shortages. Antigen tests have recently emerged as a viable alternative to detect patients with high viral loads, associated with elevated risk of transmission. While rapid lateral flow tests greatly improved accessibility of SARS-CoV-2 detection in critical areas, their manual nature limits scalability and suitability for large-scale testing schemes. The Elecsys® SARS-CoV-2 Antigen assay allows antigen immunoassays to be carried out on fully automated high-throughput serology platforms. Methods: A total of 3139 nasopharyngeal and oropharyngeal swabs were collected at 3 different testing sites in Germany. Swab samples were pre-characterized by RT-qPCR and consecutively subjected to the antigen immunoassay on either the cobas e411 or cobas e801 analyzers. Results: Of the tested respiratory samples, 392 were PCR positive for SARS-CoV-2 RNA. Median concentration was 2.95×104 (interquartile range [IQR] 5.1×102–3.5×106) copies/mL. Overall sensitivity and specificity of the antigen immunoassay were 60.5% (95% confidence interval [CI] 55.5–65.4) and 99.9% (95% CI 99.6–100), respectively. A 93.7% (95% CI 89.7–96.5) sensitivity was achieved at a viral RNA concentration ≥104 copies/mL (cycle threshold (Ct) value <29.9). Conclusion: The Elecsys SARS-CoV-2 Antigen assay reliably detected patient samples with viral loads of 10,000 copies/mL and higher. It thus represents a viable high-throughput alternative for pre-screening of patients, or in situations where PCR testing is not readily available.

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Almost two 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 infections. We screened 6113 children <18 years by nasopharyngeal swab-PCR in a low-incidence setting after general lockdown, from May 9 to June 30, 2020. 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 incomplete seroconversion in most families, with higher rates 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 nine 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 seroconversion rates 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.