As an improvement over coated microneedles, dissolving microneedles have been developed in order to eliminate sharp, biohazardous waste after vaccination (Fig. 3c) . Unlike non-dissolving (e.g., metal) microneedles coated with a vaccine formulation, dissolving microneedles are made solely of material such as polymers or sugars that will safely dissolve in the skin after insertion, which leaves behind only the microneedle patch backing. Typically, the vaccine is incorporated into the matrix of the microneedle and is released into the skin upon microneedle dissolution. Dissolving microneedles have been made using a number of different materials, including polyvinylpyrrolidone (Sullivan et al. 2008) , maltose (Kolli and Banga 2008) , carboxymethylcellulose (Lee et al. 2008 ), polylactic and/or polyglycolic acid (Park et al. 2005; Park et al. 2006 ) and dextrin (Ito et al. 2006 ). In a recent study, dissolving microneedles were prepared by encapsulating inactivated influenza vaccine in a polyvinylpyrrolidone matrix and used to immunize mice. The vaccine was gently encapsulated without significant damage to immunogenicity and was shown to generate similar antibody and cellular immune responses compared to IM injection of the same dose and provided complete protection against lethal challenge. Compared to IM injection, dissolving microneedle vaccination resulted in more efficient lung virus clearance and enhanced cellular recall responses after challenge (Sullivan et al. 2010 ). TheraJect has also developed biodegradable microneedles using carboxymethylcellulose containing various biomolecules including influenza vaccine (Oh et al. 2006 ).