Figure 2.

Determination of S- and RBD -specific antibody levels. Y-axes indicate the S- specific BAU/mL levels (left graph, ECLIA, Roche and validated with WHO NIBSC code 20/136) or the OD₄₀₅-values (middle and right graph) obtained with S- or RBD while x-axes show the respective dates of venipuncture. Dotted lines show the cut-off values of the respective tests l. The two dotted lines represent the different cut-off values of the individual test. The cut-off was set at 15.0 BAU/mL for the visit on 8 June 2021, while it was set as 0.8 BAU/mL for the visit on 17 August 2021.