Intradermal delivery of a fractional dose of influenza H7N9 split vaccine elicits protective immunity in mice and rats.

Vaccination is the most effective method of preventing the spread of the influenza virus. However, the traditional intramuscular (IM) immunization causes fear, pain, and cross infection. In contrast, needle-free (NF) immunization is quick and easy for medical personnel and painless and safe for patients. In this study, we assessed the safety and protective efficacy of NF intradermal (ID) immunization with the influenza H7N9 split vaccine (Anhui H7N9/PR8). A preliminary safety evaluation showed that ID immunization with 15 μg of the H7N9 influenza vaccine was not toxic in rats. Moreover, the antigen was metabolized more rapidly after ID than after IM immunization, as determined by in vivo imaging, and ID immunization accelerated the generation of a specific immune response. Additionally, ID immunization with a 20% dose of the H7N9 split vaccine Anhui H7N9/PR8 offered complete protection against lethal challenge by the live H7N9 virus. Taken together, our findings suggest that NF ID immunization with the H7N9 influenza vaccine induces effective protection, has a good safety profile, requires little antigen, and elicits an immune response more rapidly than does IM immunization. This approach may be used to improve the control of influenza H7N9 outbreaks.