SARS-CoV-2 Serology Across Scales: A Framework for Unbiased Estimation of Cumulative Incidence Incorporating Antibody Kinetics and Epidemic Recency

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.

Silent battles: immune responses in asymptomatic SARS-CoV-2 infection

SARS-CoV-2 infections manifest with a broad spectrum of presentations, ranging from asymptomatic infections to severe pneumonia and fatal outcomes. This review centers on asymptomatic infections, a widely reported phenomenon that has substantially contributed to the rapid spread of the pandemic. In such asymptomatic infections, we focus on the role of innate, humoral, and cellular immunity. Notably, asymptomatic infections are characterized by an early and robust innate immune response, particularly a swift type 1 IFN reaction, alongside a rapid and broad induction of SARS-CoV-2-specific T cells. Often, antibody levels tend to be lower or undetectable after asymptomatic infections, suggesting that the rapid control of viral replication by innate and cellular responses might impede the full triggering of humoral immunity. Even if antibody levels are present in the early convalescent phase, they wane rapidly below serological detection limits, particularly following asymptomatic infection. Consequently, prevalence studies reliant solely on serological assays likely underestimate the extent of community exposure to the virus.

Seroprevalence and clinical characteristics of SARS-CoV-2 infection in children with cystic fibrosis

BACKGROUND

People with cystic fibrosis (PwCF) have chronic lung disease and may be at increased risk of coronavirus disease 2019 (COVID-19)-related morbidity and mortality. This study aimed to determine seroprevalence and clinical characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in children with cystic fibrosis (CF), and to assess antibody responses following SARS-CoV-2 infection or vaccination.

METHODS

Children and adolescents with CF followed at Seattle Children's Hospital were enrolled between July 20, 2020 and February 28, 2021. SARS-CoV-2 serostatus was determined on enrollment at 6 and 11 months (±2 months) for nucleocapsid and spike IgG. Participants completed intake and weekly surveys inquiring about SARS-CoV-2 exposures, viral/respiratory illnesses, and symptoms.

RESULTS

Of 125 PwCF enrolled, 14 (11%) had positive SARS-CoV-2 antibodies consistent with recent or past infection. Seropositive participants were more likely to identify as Hispanic (29% vs. 8%, p = 0.04) and have pulmonary exacerbations requiring oral antibiotics in the year prior (71% vs. 41%, p = 0.04). Five seropositive individuals (35.7%) were asymptomatic, while six (42.9%) reported mild symptoms, primarily cough and nasal congestion. Antispike protein IgG levels were approximately 10-fold higher in participants following vaccination compared with participants who had natural infection alone (p < 0.0001) and resembled levels previously reported in the general population.

CONCLUSIONS

A majority of PwCF have mild or no symptoms of SARS-CoV-2 making it difficult to distinguish from baseline respiratory symptoms. Hispanic PwCF may be disproportionately impacted, consistent with racial and ethnic COVID-19 disparities among the general US population. Vaccination in PwCF generated antibody responses similar to those previously reported in the general population.