Among the various vaccine candidates, influenza vaccine has received the most attention by ID immunization using small arrays of coated microneedles measuring approximately 700 lm in length (Zhu et al. 2009 ). Microneedles coated with 10 lg of seasonal influenza H1N1 inactivated virus vaccine induced complete protection against lethal virus infection in mice. However, subsequent studies showed that influenza vaccine lost more than 95% of its antigenicity during the coating process (Kim et al. 2010b) . In order to maintain antigenicity, the disaccharide trehalose was added to the coating formulation to serve as a stabilizer. This enabled successful immunizations requiring smaller doses of vaccine (0.4 lg) as compared to immunizations with similar immune responses by conventional IM immunization Kim et al. 2011) . Coated microneedles also showed improved thermal stability of vaccine compared to the liquid form of vaccine (Kim et al. 2010b ). More detailed studies showed that coated microneedle vaccination with inactivated influence virus vaccine induced similar antibody IgG response, HAI titer, and neutralizing activity as conventional IM immunization in mice Kim et al. 2010b ). To account for antigenic changes to the vaccine during the coating process, vaccine coated on microneedles was dissolved off the needles and then delivered IM by injection. In this case, vaccination using microneedles showed a better primary immune response than corresponding IM immunization using the same antigen formulation ).