Extended Data Fig. 10: Comparison of linear exponential model with spline-based model in examining non-linearity of antibody decline.

a, Plotted in log10 scale. b, Plotted in original scale. The estimated trajectory from the spline model (with 4 knots placed at 10th, 40th, 60th, and 90th of observed time points) is similar with the linear exponential model for both ChAdOx1 and BNT162b2, indicating that there was no evidence of antibody decline flattening. Linear models provided better fit. Black dotted line shows the positivity threshold of 23 BAU/mL. Red dotted line shows the upper quantification limit of 450 BAU/mL.