Clinical studies assessing immunogenicity and safety of intradermally administered influenza vaccines.

IMPORTANCE OF THE FIELD: Human influenza A and B are major respiratory pathogens and cause high mortality and severe morbidity, especially in at-risk populations. Most of the vaccines are administered intramusculary or subcutaneously. Owing to vaccine shortage and low vaccine coverage, intradermal administration of vaccines has gained renewed interest. In addition, higher immune responses with the same quantity of antigen have been elicited with intradermal vaccine administration, offering dose-sparing capacity. AREAS COVERED IN THIS REVIEW: This review summarizes the immunogenicity and safety data accumulated from influenza vaccine trials where vaccines were administered intradermally. Clinical trials performed using reduced vaccine antigen doses in healthy volunteers or in at-risk populations and target groups are discussed as well as new devices for intradermal delivery of influenza vaccines. The studies addressed in this review were identified through a MEDLINE search. WHAT THE READER WILL GAIN: The review provides insights into the potential of intradermal vaccines to overcome hurdles such as vaccine shortage in view of mass vaccination campaigns. Moreover, evidence is provided of improved immunological responses after intradermal vaccination when new intradermal devices are being used. TAKE HOME MESSAGE: In the authors' opinion, intradermal vaccination can be considered an equally immunogenic, safe and feasible alternative to intramuscular and subcutaneous vaccination. The future looks promising because of the recent development of new intradermal vaccine delivery devices.