Background: Previously, Fluzone® Intradermal (ID) Vaccine (9 µg hemagglutinin [HA]/strain delivered via the BD Soluvia™ Microinjection System) was as immunogenic and safe as Fluzone vaccine (15 µg HA/strain) given intramuscularly (IM) in healthy adults 18-64 years old.
Objectives: To evaluate the safety and immunogenicity of revaccination with ID vaccine during a 2nd year follow-up vaccination protocol.
Methods: Subjects (N=1250) who had received ID or IM vaccine in the first study year were randomly assigned prior to the influenza season of the following year (2009) into 1 of 4 groups: subjects vaccinated with ID were revaccinated with ID (ID/ID, N=505) or IM (ID/IM, N=251) vaccine; subjects vaccinated with IM were revaccinated with IM (IM/IM, N=237) or ID (IM/ID, N=246) vaccine. Local and systemic reactions were recorded and immunogenicity measured at day 28 by hemagglutination inhibition (HAI) assay.
Results: After revaccination, rates of systemic reactions (headache, malaise, myalgia, fever) were comparable in all 4 groups, but local injection-site reactions (erythema, swelling, induration, pruritus, but not pain) were more frequent after receipt of ID than IM vaccine. Safety profiles were similar between the 2 groups revaccinated with ID (ID/ID and IM/ID) and between the 2 groups revaccinated with IM (ID/IM and IM/IM). Most solicited reactions in all groups were Grade 1 or 2 in intensity and resolved in 3-7 days. There were no serious adverse events related to vaccination. HAI antibody responses to A/H1N1, A/H3N2, and B were similar among all groups by geometric mean titers, and rates of seroconversion and seroprotection.
Conclusions: Revaccination with intradermal influenza vaccine was well tolerated regardless of the previous year’s vaccination regimen. Antibody responses to all 3 virus strains were comparable after ID and IM revaccination. Fluzone Intradermal Vaccine with reduced HA dose appears to be a viable alternative to standard influenza vaccines administered intramuscularly.