Vaccination by coated microneedles induced robust immunity to influenza after challenge in a mouse model (Kim et al. 2011) . Notably, microneedle-immunized mice were shown to have undetectable levels of influenza virus titer in their lungs after challenge, unlike IM immunized mice, which had virus titers at least 100-fold higher. Additional assays for immune response from corresponding lung samples such as lung cytokine and lung IgG also consistently showed microneedle immunization to be superior to IM. As evidence for microneedle-enhanced immune system memory response, the microneedle immunized group was found to have significantly higher levels of total IgG and isotypes IgG1 and IgG2a postchallenge than pre-challenge, but antibody levels in IM immunized mice were lower post-challenge than pre-challenge (Kim et al. 2011 ). In addition to improved humoral immunity, coated microneedles also induced cellular recall response such as MHC II-associated CD4 + T helper cell response ). Finally, microneedle immunization performed using a different strain of influenza (H3N2) virus vaccine induced similar complete protection against lethal challenge (Koutsonanos et al. 2009 ). Studies using virus-like particle (VLP) vaccine coated on microneedles were also performed. The VLP dose was controlled using a coating formulation including antigen concentration and a number of coating dips (Kim et al. 2010a) . When a 0.35 lg dose of VLP was delivered, microneedle vaccination induced a stronger immune response than IM, as measured by IgG, IgG subtype (IgG1, IgG2a, IgG2b), HAI, neutralizing activity, lung IgG, lung cytokine, and more suppression of lung virus infection. Microneedle immunization by VLP showed complete protection from a lethal viral challenge without major body weight loss, unlike IM after the same dose, which partially protected mice from lethal viral infection (40%) and caused significant body weight loss (Quan et al. 2010) .