Effect of age and frequency of injections on immune response to hepatitis B vaccination in drug users

Abstract

Despite the high immunogenicity of the hepatitis B vaccine, evidence suggests that immunological response in drug users is impaired compared to the general population. A sample of not-in-treatment adult drug users from two communities in Houston, TX, USA, susceptible to hepatitis B virus (HBV), was sampled via outreach workers and referral methodology. Participants were randomized to either the standard multi-dose hepatitis B vaccine schedule (0, 1, and 6 months) or to an accelerated (0, 1, and 2 months) schedule. The participants were followed for 1 year. Antibody levels were measured at 2, 6 and 12 months after enrollment in order to determine the immune responses. At 12 months, cumulative adequate protective response was achieved in 65% of the HBV susceptible subgroup using both the standard and accelerated schedules. The standard group had a higher mean antibody titer (184.6 mIU/mL vs 57.6 mIU/mL). But at 6 months, seroconversion at the adequate protective response was reached by a higher proportion of participants and the mean antibody titer was also higher in the accelerated schedule group (104.8 mIU/mL vs. 64.3 mIU/mL). Multivariate analyses indicated a 63% increased risk of non-response for participants 40 years or older (p=0.046). Injecting drugs more than once a day was also highly associated with the risk of non-response (p=0.016). Conclusions from this research will guide the development of future vaccination programs that anticipate other prevalent chronic conditions, susceptibilities, and risk-taking behaviors of hard-to-reach populations.