Multiple studies of reduced-dose delivery of influenza vaccines have been conducted, providing some of the most informative clinical data on the potential for dose-sparing through ID delivery. One study found that ID delivery of 6 lg HA per influenza strain was comparably immunogenic as the standard IM dose of 15 lg HA per strain (Belshe et al. 2004) . A later comparison of 3, 6, and 9 lg delivered both ID and IM found equivalent responses for the two delivery routes for each dose (Belshe et al. 2007) . Trials have also been conducted with influenza using novel microneedle devices to aid accurate ID delivery, as discussed in Sect. 3.2.