A systematic review of intradermal influenza vaccines.

Influenza infection is associated with many complications, which can lead to hospitalizations and death. This is particularly true for the older adults who are not able to mount as good an immune response as younger adults due to their declining immune function. As such, different strategies are being evaluated to increase immunogenicity in the older adults, including use of adjuvanted vaccines and different delivery techniques, which can enhance immunogenicity as well as potentially be dose-sparing. The objective of this paper was to conduct a systematic review of studies that evaluated the efficacy (in terms of immunogenicity) and safety of intradermal (ID) influenza vaccines compared with traditional methods of administration in the general population and the older adults. Thirteen randomized, controlled, open-label trials were included in this systematic review. Seven trials were conducted in young adults 18-60 years of age, 4 trials were studied in older subjects >60 years, and 2 trials included both young and older adults, of which one did separate analyses for both groups and one did a separate analysis for the older adult population only. We found 7 studies out of 8 for the 18-60-year olds and 4 out of 6 studies in the over 60-year olds showed comparable efficacy between ID and intramuscular (IM) administration. Two out of 6 studies in the over 60-year olds showed superiority of ID administration over IM. Rates of adverse events occurring in the first 3 days were comparable between ID and IM administration of influenza vaccines; however, when assessing adverse events occurring in the first 7 days, rates of local adverse events were consistently higher in the ID group, specifically erythema, swelling, induration, and pruritis. In conclusion, our review shows comparable efficacy between ID and IM administration of influenza vaccine in both the younger and older adults.