Rates of severe acute respiratory syndrome coronavirus 2 infection in a highly exposed South African blood donor cohort, 2022–2023
Marion Vermeulen, Ronel Swanevelder, Cordelia Mmenu, Tinus Brits, Josephine Mitchel, Eduard GrebeAbstract
Background and Objectives
A cohort of South African repeat blood donors was established to leverage the repeated presentation of blood donors for longitudinal serological surveillance of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infections and reinfection incidence in a highly exposed population.
Materials and Methods
The prospective cohort was followed from January 2022 to December 2023, with a total of 7459 blood samples from 2155 donors captured and tested using the Roche anti‐nucleocapsid (N) and anti‐spike (S) total immunoglobulin antibody (Ab) assays. First infections were identified by anti‐N seroconversion and reinfections by anti‐N boosting (≥1.5‐fold) in longitudinal testing, using a novel method to reduce misclassification from prolonged Ab maturation. Incidence was estimated, and correlates of infection were assessed using multivariable Cox proportional hazards regression.
Results
A total of 948 infection events were observed during the study period—280 first infections and 668 reinfections, with up to 4 serial infection events in one donor. Total infection incidence was estimated at 64.2 infections/100 person‐years (95% confidence interval [CI]: 60.2–68.4). In multivariable models, quartile of anti‐N reactivity was a strong correlate of protection against reinfection with an adjusted hazard ratio of 0.26 (95% CI: 0.18–0.38).
Conclusion
Longitudinal blood donor serosurveillance allowed quantification of continuing SARS‐CoV‐2 transmission after most individuals had been previously infected in the 2 years after relaxation of non‐pharmaceutical interventions.