Sara van den Berg

30 Chapter 2 considered significant. Data were analyzed using SPSS statistics 22 for Windows (SPSS Inc., Chicago, IL) and R 3.4.0 (https://www.r-project.org/) . RESULTS Characteristics of the study population In total 288 individuals were vaccinated with the pandemic influenza vaccine in the pandemic season ( Figure 1 ). CMV-serostatus was determined and 25 individuals with an equivocal CMV status were excluded from further analysis. Of the remaining 263 individuals, 171 were CMV-seropositive (65%). Groups of CMV-seropositive and CMV-seronegative individuals were comparable for sex, age and previous influenza vaccinations ( Table 1 ). In season 2010- 2011 128 of the 263 participants were vaccinated with the seasonal vaccination of which 76 (59.4%) were CMV-seropositive. Also, in the subsequent season no differences in sex, age and previous influenza vaccinations between CMV-seropositive and CMV-seronegative individuals were observed ( Table 1 ). Pandemic season Season 2010-2011 Total (n=263) a CMV+ (n=171) CMV- (n=92) Signifi- cance Total (n=128) CMV+ (n=76) CMV- (n=52) Signifi- cance Age (mean and SD) 39.9 (7.8) 39.3 (8.6) 39.5 (8.5) P=0.88 41.3 (8.1) 41.7 (7.7) 40.63 (8.6) P=0.43 Sex (% men) 45.2% 51.1% 42.1% P=0.19 48.4 % 46.1% 51.9% P=0.59 Previous influenza vaccination before pandemic season 49.0% 49.7% 47.8% P=0.80 65.6% 63.2% 69.2% P=0.57 Seasonal vaccination 2009-2010 before study 23.6% 23.4% 23.9% P=1.00 87.1% b 77.6% 78.8% P=1.00 Seasonal vaccination 2009-2010 during study 37.3% 38.0% 35.9% P=0.79 Table 1. Characteristics of study population for pandemic season and season 2010-2011. CMV-seropositive and CMV-seronegative group are compared with Student’s t-test for age and with the Fischer exact test for categorical variables. a Time point 5, 52 weeks after pandemic influenza vaccination, blood was collected of 155 participants who continued in the study for season 2010-2011. b Seasonal vaccination in 2009 before study or during study combined. Negative effect of age on influenza titers after de novo pandemic influenza vaccination We investigated if there was an effect of age on the induction of antibodies to the pandemic influenza vaccination in our study population. After pandemic vaccination, H1N1pdm influenza virus-specific antibody titers were negatively correlated with age at all time points post- vaccination except wT5 (see Supplementary Table 8 ). Representative data are depicted for T2 in Figure 2A (T2, p=0.0013 R -0.198) . Individuals are divided in three age groups for further