Fig. 4: Impact of previous SARS-CoV-2 infection and/or booster dose (third dose) on the COVID-19 vaccine-induced immune response.

Levels stratified by vaccination and infection status at Time 2 (approximately 11 months after second vaccine dose). a Plasma total immunoglobulin (Ig) levels specific to the anti-spike glycoprotein (measured in kilobinding antibody units per litre, kBAU/L). Dotted line indicates a cut-off level of 300 kBAU/L (protective level). b Saliva total immunoglobulin (Ig) levels specific to the anti-spike glycoprotein (measured in kilobinding antibody units per litre, kBAU/L). c SARS-CoV-2-specific T-cells (CD4⁺/CD4⁺ + CD8⁺) IFN-γ release plasma levels (measured in International Unit per millilitre, IU/mL). Dotted line indicates a cut-off level of 0.15 IU/mL (positive reaction). The boxplots present the lower quartile, median, and upper quartile, and the error bars indicate 95% CI. Kruskal-Wallis test was used to examine the overall differences in antibody and cellular response across different. Pairwise comparisons were performed using Dunn’s test, with adjustments made for multiple comparisons through Bonferroni correction. P < 0.05 were considered significant.