In a Phase II clinical trial, the effects of lower dose ID immunization was investigated using 3, 6, and 9 lg of hemagglutinin (ID) and 15 lg of hemagglutinin (IM). ID immunization using 3 and 6 lg of hemagglutinin induced inferior immune response as shown by HAI titer, but a dose of 9 lg showed comparable response compared to full-dose (15 lg) IM vaccination (Beran et al. 2009 ). For elderly subjects ([60 years old), a booster vaccine (15 lg) was administered due to the inferior immune system generally found in the elderly compared to younger adults (Goodwin et al. 2006) . Therefore, 15 lg of hemagglutinin was administered twice by either ID or IM routes in elderly subjects. In this phase II clinical trial, ID immunization showed significantly better immune response as determined by postimmunization GMT (geometric mean titer), seroprotection (% participants with HAI titers C40), GMTR (geometric mean ratio of post-immunization titer to pre-immunization titer), and rate of seroconversion (post-immunization titer in participants with a pre-immunization titer \10). Therefore, ID microneedle vaccination provided superior immunogenicity in a high priority population for protection from influenza due to high vulnerability (Holland et al. 2008 ). These findings were further confirmed in a phase III clinical trial for elderly persons ([60 years old), where ID immunization showed superior seroprotection, GMTR, and rate of seroconversion compared to IM after prime immunization.