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The following is a summary of “Anti-SARS-CoV-2 nucleocapsid antibodies to detect exposure to SARS-CoV-2: results from a prospective cohort study on COVID-19 vaccination,” published in the March 2025 issue of Infectious Diseases by Rasmussen et al. 

Researchers conducted a retrospective study to explore alternative population surveillance methods for assessing SARS-CoV-2 exposure following the decline of general testing.  

They evaluated N-antigen antibodies as a marker of SARS-CoV-2 exposure in a vaccinated Swedish population. Serum samples were collected and analyzed for N-antigen antibodies using the mesoscale system. A nonlinear mixed-effects model, accounting for multiple measurements per individual, was applied to estimate the half-life of N-antigen antibodies.  

The results showed that 3,202 participants (median age 31 years) were recruited from April 2021 to February 2022 across 4 vaccination centers in Skåne, Sweden, of these, 2,999 had at least 1 valid N-antigen antibody measurement. The estimated half-life of N-antigen antibodies was 59 days (95% CI: 55–64 days), with a range of 24 to 174 days. Repeated N-antigen antibody measurements effectively detected SARS-CoV-2 infection. A 2-fold increase in antibody levels had a sensitivity of 91%, while a 16-fold increase showed a specificity of 91%. The area under the curve (AUC) for predicting infection was 0.88 (95% C.I. 0.86–0.90).  

Investigators concluded that serial N-antigen antibody monitoring proved useful in evaluating SARS-CoV-2 exposure, which could enhance transmission tracking and inform vaccination strategies. 

Source: tandfonline.com/doi/full/10.1080/23744235.2025.2479139