Prevalence of SARS-CoV-2 antibodies at the University hospital Heidelberg and correlation with SARS-CoV-2 incidence

Background: Since the onset of the SARS-CoV-2 pandemic in late 2019, many studies suggest that actual infection rates may far exceed reported cases. Therefore, this study provides a comprehensive overview of anti-SARS-CoV-2 antibody measurements and their significance in epidemiological surveillance, especially regarding the true extent of SARS-CoV-2 infections, allowing more detailed insights into the dynamics of the pandemic.

Methods: Antibodies were measured using the Elecsys® Anti-SARS-CoV-2 assay for the nucleocapsid (N) protein and the SARS-CoV-2 IgG (sCOVG) assay for the spike (S) protein. A total of 25197 specimens from University Hospital Heidelberg were analyzed between May 2020 and December 2023, with 16957 samples measured for both antibodies, 2756 for anti-N only, and 5484 for anti-S only.For the epidemiological tracing of the SARS-CoV-2 incidence we analyzed changes in the anti-N positivity rate and anti-S positivity rate within our tertiary hospital setting across consecutive quarters.

Results: Anti-N measurements allowed for a retrospective analysis of SARS-CoV-2 epidemiological developments, revealing significant changes (p <0.05) in the anti-N positivity rate following incidence peaks (increase) and low incidence periods (decrease) with only three non-significant transitions.On the other hand, the anti-S positivity rate showed only four significant transitions between consecutive quarters.

Conclusion: The anti-N positivity rate is an effective and straightforward retrospective serological tool for tracking epidemiological trends, while the anti-S rate is influenced by vaccination and epidemiology as well, making it inept for the tracing of epidemiological changes. Although the recent development in SARS-CoV-2 epidemiology with increasing intervals between infection waves already provide an enhanced statistical robustness, we recommend the determination of the anti-N positivity rate in larger study populations.