Eliminating the hypodermic needle from vaccination is a major objective of public health, given that close to one million people die each year from disease transmission from contaminated needles (Miller and Pisani 1999; Kermode 2004) . Microneedles are a step in the right direction, but still generate biohazardous sharp waste, with the exception of dissolving microneedles. Projectile delivery and patchbased methods eliminate needles and therefore offer an improved safety profile. Thermal ablation +++ + +++ + + ++ a +++ requires little or no personnel training, ++ requires personnel training, + requires personnel training and maintenance of a dedicated device b +++ almost 100% in skin, ++ [50% in skin, + \50% in skin c +++ no biohazardous sharp waste, ++ microscopic biohazardous sharp waste, + macroscopic biohazardous sharp waste d +++ in widespread clinical practice, ++ published vaccination data in humans, + preclinical e +++ no reformulation required, ++ possible new liquid formulation required, + reformulation required to produce solid-state vaccine f +++ inexpensive disposable device, ++ specialty disposable device, + reusable device. Perinjection cost of reusable devices will depend on the number of times the device can be used and the cost of any disposable components However, some ID delivery methods can cause added tissue trauma to the skin (Bremseth and Pass 2001) . Most of the new methods of ID vaccination require significant technology development. While jet injection is already in widespread clinical use, many other technologies are only in the preclinical stage of development for vaccination. That being said, many of those technologies are in much later stage of development or use for non-vaccine applications, which will facilitate their adaptation to ID vaccination. Most of the new ID vaccination technologies also require vaccine reformulation. Hollow microneedle, jet and tattoo-based methods may use standard, currently available liquid formulation, but in some cases will need to be concentrated or otherwise modified. The other methods mostly use a solid-state vaccine formulation, which offers likely advantages in terms of vaccine stability during storage, but, however, requires significant reformulation, with associated research, regulatory, and manufacturing hurdles. Finally, device cost is a significant consideration, given that a hypodermic needle and syringe are extremely inexpensive, disposable devices. Microneedle systems and some of the patch-based methods are expected to have low manufacturing cost in mass production. However, many of the other technologies require multiple device components, which may be engineered into disposable devices with added cost or reusable devices with disposable components that require an initial investment that can be amortized over many patients.