The comparability of Anti-Spike SARS-CoV-2 antibody tests is time-dependent: a prospective observational study

Perkmann, T.; Mucher, P.; Perkmann-Nagele, N.; Radakovics, A.; Repl, M.; Koller, T.; Schmetterer, K. G.; Bigenzahn, J. W.; Leitner, F.; Jordakieva, G.; Wagner, O. F.; Binder, C. J.; Haslacher, H.

Objectives Various commercial anti-Spike SARS-CoV-2 antibody tests are used for studies and in clinical settings after vaccination. An international standard for SARS-CoV-2 antibodies has been established to achieve comparability of such tests, allowing conversions to BAU/ml. This study aimed to investigate the comparability of antibody tests regarding the timing of blood collection after vaccination. Methods For this prospective observational study, antibody levels of 50 participants with homologous AZD1222 vaccination were evaluated at 3 and 11 weeks after the first dose and 3 weeks after the second dose using two commercial anti-Spike binding antibody assays (Roche and Abbott) and a surrogate neutralization assay (sVNT). Results The correlation between Roche and Abbott changed significantly depending on the time point studied. Although 3 weeks after the first dose, Abbott provided values three times higher than Roche, 11 weeks after the first dose, the values for Roche were twice as high as for Abbott, and 3 weeks after the second dose even 5-6 times higher. Conclusions The comparability of quantitative anti-Spike SARS-CoV-2 antibody tests is highly dependent on the timing of blood collection after vaccination. Therefore, standardization of the timing of blood collection might be necessary for the comparability of different quantitative SARS-COV-2 antibody assays.