Sara van den Berg

32 Chapter 2 Higher residual protection rates after pandemic influenza vaccination in CMV-seropositive individuals than in CMV-seronegative individuals Subsequently, we investigated whether there was an effect of CMV-serostatus on the protection rate, as defined by antibody titer ≥ 40 HAU, against influenza virus after influenza vaccination [41]. Shortly after vaccination, no effect of CMV-serostatus on the protection rate was observed. However, CMV-seropositivity was associated with enhanced six months and one year protection rates after pandemic vaccination. The percentage protected individuals is significantly higher for CMV-seropositive individuals than for CMV-seronegative individuals, both 26 (p=0.047) and 52 weeks (p=0.044) after pandemic vaccination ( Figure 3B ) (unadjusted data in Supplementary Figure 1B ). Together, this suggests that latent CMV infection did not impair the protection rate after influenza vaccination, but if anything, might be beneficial for persistence of protection after the de novo influenza vaccination. High anti-CMV IgG levels as surrogate marker of CMV reactivation are not associated with impaired pandemic influenza vaccine response in CMV- seropositive individuals To study in the CMV-seropositive individuals whether the frequency of CMV reactivation has a negative effect on the influenza antibody responses, anti-CMV IgG levels were used as a surrogate marker of CMV reactivation [25, 42] and associated with the influenza antibody response to vaccination. To this end, CMV-seropositive individuals with low anti-CMV IgG levels (≤ 30U/ml), medium anti-CMV IgG levels (> 30U/ml, ≤ 90U/ml) or high anti-CMV IgG levels (> 90U/ml) were compared for their influenza antibody titer and protection rate both unadjusted ( Supplementary Figures 1C, D ) and with the GEE model ( Supplementary Table 3 ). No differences were observed between anti-CMV IgG groups in the H1N1pdm influenza titers or protection rate after the pandemic vaccination ( Figure 3 C, D ). This indicates that despite a negative effect of age on the antibody response to the pandemic vaccination ( Figure 2 ), no signs of impairment by CMV reactivation were observed. Also this shows that the positive effect of CMV-status on long-term protection after pandemic influenza vaccination ( Figure 3B ) could not be explained by differences in anti-CMV IgG groups within CMV-seropositive individuals. No effect of age or CMV-serostatus on seasonal influenza vaccination with H1N1pdm and H3N2 The same analyses for the effect of age and latent CMV infection on influenza vaccination were performed for the 128 individuals that continued with the study and were vaccinated in season 2010-2011 with the seasonal influenza vaccination containing the same H1N1pdm strain and an H3N2 strain. A trend of a negative effect of age on the H1N1pdm memory response was observed, but no significant differences in antibody titers for H1N1pdm or H3N2 were found between age groups at any time point after vaccination in season 2010- 2011 (e.g.T2 respectively p=0.101 and p=0.434 ( Figure 4A ). Both the influenza antibody titer and the protection rate did not differ between CMV-seropositive and CMV-seronegative individuals ( Figure 4B, C, D; Supplementary Table 4, 6 ). Surprisingly, influenza antibody