Fig. 2: The QIV vaccination induced HI titers.

The pre-QIV and 28 days post-QIV vaccination H3N2 (A) and H1N1 (B) specific HI GMT titers split by age group (young adults n = 56, middle-aged adults n = 94, older adults n = 157). The boxplots indicate the median and interquartile range. All individual values, from min to max, are plotted behind the boxplot. The pre- and post-vaccination timepoints were compared between the different age groups with the Kruskall–Wallis test and corrected for multiple comparisons with Bonferroni correction. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. The exact p-values at the 28 days post-vaccination time are: YA vs MA: p-value = 0.002, YA vs OA: p-value < 0.0001. C The long-term H3N2-specific HI titers per age groups plotted at the timepoint of sampling. D The longitudinal H3N2 HI-specific titers. The lines indicate the mean and standard error of the mean. In both (C and D) n = 52 young adults, n = 87 middle-aged adults, and n = 142 older adults were included and for clarity reasons, no statistics are indicated in these graphs. The gray dotted lines indicate an HI titer of 40, the cut-off level for protection. Source data are provided as a Source data file.