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Background and Objectives: Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) serosurveys are typically analysed by applying a fixed threshold for seropositivity ('conventional approach'). However, this approach underestimates the seroprevalence of anti‐nucleocapsid (N) in vaccinated individuals—who often exhibit a difficult‐to‐detect anti‐N response. This limitation is compounded by delays between the onset of infection and sample collection. To address this issue, we compared the performance of four immunoassays using a new analytical approach ('ratio‐based approach'), which determines seropositivity based on an increase in anti‐N levels. Materials and Methods: Two groups of plasma donors and four immunoassays (Elecsys total anti‐N, VITROS total anti‐N, Architect anti‐N Immunoglobulin G (IgG) and in‐house total anti‐N) were evaluated. First‐group donors (N = 145) had one positive SARS‐CoV‐2 polymerase chain reaction (PCR) test result and had made two plasma donations, including one before and one after the PCR test (median = 27 days post‐PCR). Second‐group donors (N = 100) had made two plasma donations early in the Omicron wave. Results: Among first‐group donors (97.9% vaccinated), sensitivity estimates ranged from 60.0% to 89.0% with the conventional approach, compared with 94.5% to 98.6% with the ratio‐based approach. Among second‐group donors, Fleiss's κ ranged from 0.56 to 0.83 with the conventional approach, compared with 0.90 to 1.00 with the ratio‐based approach. Conclusion: With the conventional approach, the sensitivity of four immunoassays—measured in a predominantly vaccinated population based on samples collected ~1 month after a positive test result—fell below regulatory agencies requirement of ≥95%. The ratio‐based approach significantly improved the sensitivities and qualitative agreement among immunoassays, to the point where all would meet this requirement. [ABSTRACT FROM AUTHOR]

Background and Objectives: Eight published studies modelled the impact of changing from a lifetime to time‐limited deferral for men who have sex with men (MSM); each predicted greater risk impact than has been observed. This study uses these previous efforts to develop an 'optimized' model to inform future changes to MSM deferrals. Materials and Methods: HIV residual risk was calculated using observed HIV incidence/prevalence prior to the change in MSM deferral, then with the additional MSM expected under a 12‐month deferral for five compliance scenarios, and finally using data observed after implementation of the deferral. Monte Carlo simulation calculated 95% confidence intervals (CI). Results: The architecture of reviewed models was sound, and two were selected for combination into the optimized model. HIV risk estimated by this in the UK under MSM lifetime deferral was 0·102 (95% CI: 0·050–0·172) per million. The model predicted from a 27·8% decrease to a 47·6% increase depending upon compliance pre‐implementation of the 12‐month deferral. A decrease of 0·9% was observed post‐implementation. For Canada, HIV risk under a 5‐year deferral was 0·050 (95% CI: 0·00003–0·122) per million. Pre‐implementation of the 12‐month deferral, the model predicted from 30·2% decrease to 10‐fold increase. A decrease of 47·0% was observed after implementation. Conclusion: The optimized model predicted HIV risk under 12‐month MSM deferral in UK and Canada would remain low, and this was confirmed post‐implementation. While the model is adaptable to other deferral scenarios, improved data quality would improve precision, particularly estimates of incidence in individuals likely to donate. [ABSTRACT FROM AUTHOR]