Sara van den Berg

28 Chapter 2 (Solvay, the Netherlands), it took place at least three weeks prior to the study or at the end of visit at time point 3 of the study. In season 2010-2011, individuals received the seasonal trivalent subunit vaccine Influvac 2010-2011, containing the influenza A vaccine strains A/ California/7/2009(H1N1pdm09) and A/Perth/16/2009(H3N2) (Solvay, the Netherlands). Blood was collected before vaccination (T1), three weeks after vaccination (T2) and 20 weeks after vaccination (T3). Figure 1. Study schedule. Participants received in the pandemic season two monovalent influenza H1N1pdm vaccinations with a three week interval (A). In total, 263 CMV-seropositive and CMV-seronegative individuals were vaccinated. 155 participants continued for the subsequent year in the study (T5 season 1). In the season 2010-2011, 128 individuals were vaccinated (T1 season 2) with the seasonal trivalent influenza vaccination which contained among others the same H1N1pdm vaccine strain and an H3N2 vaccine strain (B) . Arrows (↓) indicate the moment of vaccination. Time points (T) indicate the moment of blood withdrawal. For each time point, the number (N) of individuals with data of influenza antibody levels are indicated. Assessment of serum anti-CMV antibody titers Anti-CMV IgG antibody concentrations were measured using a commercial ELISA assay (IBL international GMBH, Hamburg, Germany) according to manufacturer’s instructions. Participants with a CMV antibody level of ≥ 12U/ml or higher were considered CMV- seropositive, a level of ≤ 8U/ml were considered CMV-seronegative and a level between 8U/ml and 12U/ml was considered equivocal and these participants were excluded for further analysis. CMV-seropositive individuals were divided in low anti-CMV levels (≤ 30U/ml), medium anti-CMV levels (> 30U/ml, ≤ 93U/ml) or high anti-CMV levels (> 93U/ml) according to the standards in the CMV ELISA kit.