Hollow microneedles have also been developed as multi-needle arrays, which have involved shorter needles (\ \1 mm) produced by novel microfabrication techniques, including laser micromachining (Davis et al. 2005) , silicon-based MEMS technique using deep reactive-ion etching (Gardeniers et al. 2003; Roxhed et al. 2007) , integrated lithographic molding technique (Luttge et al. 2007) , deep X-ray photolithography (Perennes et al. 2006) , photolithography with micromolding technique ), drawing lithography with viscoelastic polymer ) and others. In addition, glass hollow microneedles have been fabricated by drawn glass micropipette techniques (Wang et al. 2006) . A recently developed hollow microneedle array (MicronJet from NanoPass Technologies) was used in a human clinical trial involving healthy adults ). This device consists of a row of four hollow silicon microneedles that are 450 lm in length (Fig. 1f) . In this study, ID injection with the array using 20 and 40% of the IM dose (15 lg) induced similar immune response as measured by GMT increase, seroconversion rate, and seroprotection rate.