Long-term Detection of SARS-CoV-2 Antibodies after Infection and Risk of Re-Infection.

Objectives: To evaluate long-term sensitivity for detection of total antibodies against SARS-CoV-2. Methods: From week 41, 2020, through week 26, 2021, all Danish blood donations were tested for SARSCoV-2 antibodies with the Wantai assay. The results were linked with polymerase chain reaction (PCR) test results from the Danish Microbiological Database (MiBa). Results: During the study period, 105,646 non-vaccinated Danish blood donors were tested for SARSCoV-2 antibodies, and 3,806 (3.6%) had a positive PCR test before the blood donation. Among the donors with a positive PCR test, 94.2% subsequently also had a positive antibody test. The time between the positive PCR test and the antibody test was up to 15 months and there was no evidence of a decline in proportion with detectable antibodies over time. A negative serological result test was associated with a higher incidence of re-infection (Incidence Rate Ratio = 0.102 (95% confidence interval (CI): 0.039-0.262)). Conclusion: Among healthy blood donors, 94.2% developed SARS-CoV-2 antibodies after infection, and a lack of detectable antibodies was associated with re-infection. (C) 2022 The Author(s). Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.