Antibody responses after dose-sparing intradermal influenza vaccination

Reduced-dose intradermal (ID) influenza vaccination is an attractive approach to increase availability of vaccine supply in an event of vaccine shortage. We conducted a randomized open-label study, in which 500 subjects were randomly assigned to receive an ID injection of 0.1 ml dose of inactivated split-virion influenza vaccine or an IM injection of 0.5 ml dose. The subjects who had hemagglutination inhibition (HI) antibody titer of at least 1:40 at day 28 post-vaccination in ID and IM groups were 93.3% versus 98.0% for influenza A(H1N1) virus, 86.3% versus 95.0% for A(H3N2) virus, and 43.5% versus 57.0% for influenza B virus. Subjects in the ID group had an increase in geometric mean titer by a factor of 16 for the H1N1 strain, 8 for the H3N2 strain, and 2 for the B strain on day 28, as compared with respective increase in the IM group of 31, 20, and 3. Local reactions were significantly more frequent among subjects in the ID group than those in the IM group, but the reactions were mild and transient. In this study, ID administration of one-fifth dose of influenza vaccine elicited significantly lower levels of antibody response as compared to full-dose IM injection. However, the antibody responses elicited by the ID vaccination were still sufficiently high to meet the requirement guidelines of the European Committee for Proprietary Medicinal Products (CPMP) for the annual relicensure of influenza vaccines.