Antibody response to SARS-CoV-2 for more than one year - kinetics and persistence of detection are predominantly determined by avidity progression and test design.

BACKGROUND: Antibody detection of SARS-CoV-2 requires an understanding of its variation, course, and duration. METHODS: Antibody response to SARS-CoV-2 was evaluated over 5-430 days on 828 samples across COVID-19 severity levels, for total antibody (TAb), IgG, IgA, IgM, neutralizing antibody (NAb), antibody avidity, and for receptor-binding-domain (RBD), spike (S), or nucleoprotein (N). Specificity was determined on 676 pre-pandemic samples. RESULTS: Sensitivity at 30-60 days post symptom onset (pso) for TAb-S/RBD, TAb-N, IgG-S, IgG-N, IgA-S, IgM-RBD, and NAb was 96.6%, 99.5%, 89.7%, 94.3%, 80.9%, 76.9% and 92.8%, respectively. Follow-up 430 days pso revealed: TAb-S/RBD increased slightly (100.0%); TAb-N decreased slightly (97.1%); IgG-S and IgA-S decreased moderately (81.4%, 65.7%); NAb remained positive (94.3%), slightly decreasing in activity after 300 days; there was correlation with IgG-S (Rs = 0.88) and IgA-S (Rs = 0.71); IgG-N decreased significantly from day 120 (15.7%); IgM-RBD dropped after 30-60 days (22.9%). High antibody avidity developed against S/RBD steadily with time in 94.3% of patients after 430 days. This correlated with persistent antibody detection depending on antibody-binding efficiency of the test design. Severe COVID-19 correlated with earlier and higher antibody response, mild COVID-19 was heterogeneous with a wide range of antibody reactivities. Specificity of the tests was ≥99%, except for IgA (96%). CONCLUSION: Sensitivity of anti-SARS-CoV-2 assays was determined by test design, target antigen, antibody avidity, and COVID-19 severity. Sustained antibody detection was mainly determined by avidity progression for RBD and S. Testing by TAb and for S/RBD provided the highest sensitivity and longest detection duration of 14 months so far.

In vitro diagnostics for screening the blood supply: the new European regulation for IVD and the WHO IVD prequalification programme.

Blood transfusion remains a routine life-saving medical procedure that helps replace blood lost due to surgery, injury or disease. The quality of transfused blood is crucial in this process as blood donors must be free of transfusion-transmissible infections and donated blood should be compatible to that of the recipient. The quality of donated blood could be affected by the quality of in vitro diagnostic medical devices (IVDs) used in the screening process. Consequently, the need for high-quality, safe and well-performing IVDs for use in transfusion medicine arises, accompanied by the need for tight regulations in this domain. In the European Union, the new IVD Regulation will replace the existing IVD Directive within a five-year transitional period. Manufacturers of IVDs are expected to fully comply with the new Regulation by 26 May 2022. In this review, we address the major differences relating to marketing authorization and testing between this new Regulation and its predecessor. We further present the main elements of the prequalification assessment introduced by the WHO for IVDs, including disease-specific IVDs for blood screening laboratories.