Dry influenza vaccines: towards a stable, effective and convenient alternative to conventional parenteral influenza vaccination.

Cold-chain requirements, limited stockpiling potential and the lack of potent immune responses are major challenges of parenterally formulated influenza vaccines. Decreased cold chain dependence and stockpiling can be achieved if vaccines are formulated in a dry state using suitable excipients and drying technologies. Furthermore, having the vaccine in a dry state enables the development of non-parenteral patient friendly dosage forms: microneedles for transdermal administration, tablets for oral administration, and powders for epidermal, nasal or pulmonary administration. Moreover, these administration routes have the potential to elicit an improved immune response. This review highlights the rationale for the development of dried influenza vaccines, as well as processes used for the drying and stabilization of influenza vaccines; it also compares the immunogenicity of dried influenza vaccines administered via non-invasive routes with that of parenterally administered influenza vaccines. Finally, it discusses unmet needs, challenges and future developments in the field of dried influenza vaccines.