SARS-CoV-2 antibodies persist long after infection

The majority of patients who contract SARS-CoV-2 infection develop antibodies, which remain in the blood for up to 15 months after infection, a study has found. Meanwhile, a negative antibody test is linked to re-infection.

Researchers screened more than 200,000 blood donations from Danish blood donors during the SARS-CoV-2 epidemic, with the aim of evaluating the persistence of total anti-SARS-CoV-2 antibodies after real-time polymerase chain reaction (PCR)-confirmed SARS-CoV-2 infection, risk factors for undetectable antibodies, and rate of re-infection among seropositive and seronegative individuals. Blood samples were tested using the Wantai assay.

Overall, 105,646 nonvaccinated Danish blood donors were tested for SARS-CoV-2 antibodies, of whom 3,806 (3.6 percent) had a positive PCR test prior to the blood donation. In the group of donors with a positive PCR test, 3,587 individuals subsequently had a positive antibody test subsequently (overall sensitivity, 94.2 percent).

Time between positive PCR test and antibody test was up to 15 months. There was no evidence of decline in the proportion of samples with detectable antibodies over time. Regression analysis showed no correlation between a positive antibody test and days since infection (risk ratio, 1.00, 95 percent confidence interval [CI], 1.00–1.00; p=0.10).

On the other hand, a negative serological result test contributed to higher incidence of re-infection (incidence rate ratio, 0.102, 95 percent CI, 0.039–0.262).

The researchers underscored that the presence of antibodies does not necessarily translate to protective immunity, and antibody titres were not known. Furthermore, more than 60 percent of the re-infections reported in the cohort occurred among individuals with detectable antibodies.