Fig. 5

Classification of SARS-CoV-2 spike protein variants by principal component and correlation coefficient analysis. NT50 values for each serum/virus pair were log-scale transformed and assembled into vectors for each SARS-CoV-2 variant, resulting in an 8 × 8 matrix. The 1st and 2nd major axes were plotted using Axes3D (left panel). A Spearman correlation coefficient (R) matrix of all virus strains is shown in the form of a heatmap (right panel). The scale bar represents the correlation coefficient. Red indicates a positive correlation between virus variants neutralized by different sera while blue indicates a negative correlation. a Neutralization data for sera sampled 14 days after the third dose. b Neutralization data of sera sampled 90 days (28 days for Mu) after the third dose. c Neutralization data of sera sampled 14 days after the fourth dose (Beta booster). d Neutralization data of sera sampled 14 days after the fourth dose (Omicron booster). Instead of 90 days, the booster dose was administered 28 days after the 3rd dose