Anti-HBs antibody GMCs at year 4 were 42.3, 23.6, and 13.7 mIU/mL in the three groups, respectively. One month after the additional dose of hepatitis A-containing vaccine, ≥99.4% of subjects in all

the groups were seropositive VX-809 cell line for anti-HAV antibodies. Anti-HAV response rates were 98.2% in the HAB group, 97.6% in the ENG + HAV group, and 99.4% in the HBVX + VAQ group. One month after the additional dose of hepatitis B-containing vaccine, 95.2% of subjects in the HAB group had antibody concentrations ≥10 mIU/mL compared with 90.5 and 85.3% in the ENG + HAV and HBVX + VAQ groups (p = 0.1367 and p = 0.0026, respectively) (Figure 1B). Corresponding anti-HBs GMCs were 7233.7, 1242.5, and 1075.1 mIU/mL. Overall anti-HBs response rates were 93.4% in the HAB group, 88.1% in the ENG + HAV group, and 83.4% in the HBVX + VAQ group (p = 0.1305 and p = 0.0054, respectively). In subjects with anti-HBs antibody Proteasome inhibitor concentration <3.3 mIU/mL prior to administration of the additional vaccine dose, 82.1, 82.0, and 72.6% achieved an anti-HBs concentration ≥10 mIU/mL post-vaccination. In the three groups, virtually all seronegative subjects who failed to respond to the additional dose and reach the cut-off of 10 mIU/mL were already nonresponders, or very low

responders, to primary vaccination. Exploratory subgroup analyses showed hepatitis A and B seropositivity rates at year 4 to be slightly lower in subjects aged ≥61 years, with a BMI ≥30 kg/m2, receiving concomitant medication or with a current concomitant medical condition. No consistent effects of any of these factors on response to the additional vaccine dose(s) were observed (data not shown). We assessed persistence of immune response to a combined hepatitis A/B vaccine in adults aged >40 years. The study population can be considered representative of the general

population in this age group, with a high proportion of subjects being overweight, having underlying GBA3 medical conditions, or receiving concomitant medication. The differences in immune response between the combined hepatitis A/B vaccine and monovalent vaccines previously observed after primary vaccination6 were found to be maintained over time. As described in another follow-up study of this combined hepatitis A/B vaccine in this population,7 anti-HAV seropositivity rates remained high in all groups over the 4 years of follow-up. At year 4, anti-HBs rate ≥10 mIU/mL and anti-HBs GMCs were highest in subjects who received the combined vaccine, although these were lower than have been reported in younger adults 10 years after administration of this vaccine.8 The lower anti-HBs antibody response rates observed in the HBVX + VAQ group at all time-points may be due to the reduced HBsAg content and adjuvant composition of the hepatitis B vaccine in this group.