Publication date: Jul 26, 2024

Conventional serological approaches lack sensitivity for the detection of recent SARS-CoV-2 infections in vaccinated individuals, as these individuals exhibit a blunted anti-nucleocapsid (N) response. This limitation was recently addressed by the development of a “ratio-based approach”, which compares longitudinally collected specimens. Here, we used this approach to estimate the incidence of SARS-CoV-2 infection and reinfection in QucE9bec (Canada) during the Omicron wave. Consenting plasma donors were included if they donated plasma before December 15, 2021 and during six consecutive periods of ~ 3 months between December 15, 2021 and July 7, 2023 (study period). Anti-N levels were measured with an enzyme-linked immunosorbent assay, and seroconversion was characterized by a ratio of ≥ 1. 5 between the optical density of two consecutive samples. Among the 254 donors, the adjusted proportion of donors (95% confidence interval [CI]) with a new infection ranged between 18. 1% (13. 2‒23. 0) and 24. 2% (18. 8‒29. 7) over Periods 1-5 and fell to 7. 9% (4. 9‒11. 0) during Period 6. During the study period, the proportion of newly infected donors decreased among those aged 

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Original Article