Vaccine immunogenicity in injecting drug users.

Martin Schmidt commented on a Review by Stefan Baral and colleagues on vaccine immunogenicity in injecting drug users; however, Schmidt’s criticism was actually directed at our paper. The fi rst criticism about the lack of seroconversion for antibody to hepatitis B virus core antigen in the vaccinated group of injecting drug users is the only remark with any foundation: only one seroconversion happened and not two as stated. The second patient actually received only two doses, which are thought insuffi cient for adequate protection. That Schmidt affi rms that our article “did not include any mention of suboptimum levels of [hepatitis B virus surface antigen specifi c antibodies] following hepatitis B vaccination”, leads us to think that he did not read the paper carefully. At least half of the discussion is dedicated to this specifi c problem. Lastly, Schmidt judges that our study is a simple communication of an experience, but we believe that it met the criteria for being a cohort study. Its strength relies on the fact that it remains the only study that has prospectively evaluated hepatitis B vaccination effi cacy among injecting drug users. As underlined by Baral and colleagues, vaccine schedules used in the healthy general population are proposed for injecting drug users, who are considered immunologically inadequate. Obviously, it is easier to study the immune response in small selected groups of injecting drug users. However it is much more complex to do a year-long follow-up in a population that is so prone to changes in residence, incarceration, and premature death. This is a research specialty that is usually neglected and diffi cult to take forward, and further research is needed.