An early prototype of the BD microneedle system was first tested in a clinical study examining influenza vaccine delivery in healthy adults (18-60 yrs) and elderly adults ([60 yrs) (Belshe et al. 2004) . In this study, 6 lg of hemagglutinin was delivered by ID injection and compared to a full dose (15 lg) delivered by IM immunization. It was found that in younger participants, ID immunization was not significantly different from immunization by IM, as shown by geometric mean hemagglutination inhibition (HAI) titers. However, ID administration showed lower HAI titers than IM in elderly patients. Further evaluation of ID microneedle vaccination against influenza was performed in clinical studies of healthy adults (18-57 yrs) (Leroux-Roels et al. 2008; Beran et al. 2009 ) and elderly persons ([60 yrs) (Holland et al. 2008; Arnou et al. 2009 ). For healthy adults, 9 lg of hemagglutinin (H1, H3, and B strains) was delivered by ID injection and was compared to a 15 lg IM immunization. This study confirmed previous results that reduced-dose ID injection was equally immunogenic as full-dose IM injection (Leroux-Roels et al. 2008) .