Intradermal delivery for vaccine dose sparing: overview of current issues

There is a wide range of methods and technologies aimed at improving human vaccine products and the way they are delivered. Some of these have the potential to increase vaccine effectiveness in specific populations and may furthermore help to increase vaccine access, reduce costs, and ease the logistical burdens of immunization programs, especially in low-resource settings. One strategy under evaluation is the use of intradermal (ID) delivery of vaccines, which has been shown to result in dose sparing with some vaccines. Novel ID delivery devices could enable needle-free and therefore safer and more reliable ID administration than current ID injection methods, facilitating ID delivery and dose sparing with existing or new vaccines. There are promising clinical data with some vaccines that highlight the potential of reduced-dose immunization via the ID route. And more studies are under way. However, a number of clinical and technical research as well as operational challenges exist, including establishing the optimal doses for different vaccines, reformulating to adjust antigen concentration or add preservatives, matching vaccine vial volume to session size, working with vaccine manufacturers to achieve regulatory clearance for ID delivery, and developing ID delivery devices suitable for the varying scenarios of use of different vaccines. These will need to be addressed before the benefits of ID delivery and the impact of novel ID delivery technologies on human health are fully realized.