This randomized trial compared the immunogenicity of 60% dose intradermal (ID) influenza vaccination to standard intramuscular (IM) vaccination of full-dose or 60% dose vaccine. Pre- and postvaccination measurements in the hemagglutination inhibition antibody (HAI) titer were compared. Participants who received reduced-dose vaccine were revaccinated with full-dose IM vaccine.

This study was an open-label randomized trial consisting of community-dwelling adults 65 years and older living in Puget Sound area in Washington State. Subjects were enrolled and randomly assigned to receive licensed, 2007-2008 Northern Hemisphere TIV vaccine (Fluzone, lot U2440AA; Sanofi Pasteur) containing concentrations of hemagglutinin of each of A/Solomon Islands/3/2006 (A/H1N1), A/Wisconsin/67/2005 (A/H3N2), and B/Malaysia/2506/2004 (B): 15 ug/0.5 mL by the IM route, 9 ug/0.3 mL by the ID or IM route, or 4.5 ug/0.15 mL given twice by ID route to the nondominant arm. A block randomization scheme (1:1:1:1), stratified by sex, was used. For IM vaccination, 0.3 mL or 0.5 mL of vaccine was removed from a multidose (5 mL) vial through a 25-gauge, 1-inch detachable needle (Becton Dickinson) and was injected into the deltoid muscle at a 90 degree angle to the skin. For ID vaccination, 0.3 mL or 0.15 mL was drawn by a TB syringe through a 25-gauge, 5/8-inch needle (Terumo Medical). The needle was inserted at a 15 degree angle to the skin overlying the deltoid of the arm. The vaccine was slowly injected until all material was expelled and induration appeared. Subjects randomized to the 0.15-mL group received 2 side-by-side ID injections 3 cm apart. Participants returned at 4 weeks to determine postvaccination antibody titers. At this follow-up visit, those assigned to reduced dose IM or ID influenza vaccinations then received full-dose IM influenza vaccination. These participants returned in another 4 weeks to repeat HAI titers. A nonrandomized subset of subjects (based on availability and willingness to participate) returned at 14 days after initial vaccination for T cell assays in an exploratory substudy to examine cellular immune response.

Inclusion Criteria:

• Ambulatory, medically stable persons 65 years of age or older
• Able to read and understand informed consent
• Available during the trial period and for follow-up
• Able to understand and comply with planned study procedures
• Able to be contacted by telephone for follow-up of adverse events

Exclusion Criteria:

• Known allergy to eggs or other components of vaccine (i.e., thimerosal)
• History of Guillain-Barré Syndrome (GBS)
• Has a confirmed or suspected immunodeficient or immunosuppressive condition (including congenital or acquired immunosuppressive therapy, and human immunodeficiency virus [HIV])
• End-stage renal disease requiring hemodialysis
• Active neoplastic disease or history of any hematologic malignancy (except localized skin or prostate cancer that is stable in the absence of therapy)
• Acute or chronic condition that (in the opinion of the investigator) would render vaccination unsafe or would interfere with the evaluation of responses (including but not limited to the following: known chronic liver disease, significant renal disease, oxygen-dependent chronic lung disease, New York Heart Association Functional Class III or IV, unstable or progressive neurologic disorder, insulin controlled diabetes mellitus)
• Use of experimental vaccines within the month prior to study entry, or expected use of experimental or licensed vaccines or blood/blood products during the duration of the study.
• Receipt of immunoglobulin or other blood product within 3 months prior to enrollment
• Receipt of other licensed vaccines within the preceding 4 weeks
• History of a severe reaction following influenza vaccination
• Current or planned participation in a research study of an investigational drug. Participation in research studies that involve use of licensed drugs, for either approved or investigational indications, will be permitted with the approval of the PI, as will participation in research studies that do not involve vaccines or medications.
• Current use or previous chronic administration, defined as >14 days during the previous six months, of immunosuppressants or other immune-modifying drugs. (For oral or injected corticosteroids, the immune-modifying dose is defined as prednisone or its equivalent >10 mg/day or >800mcg per day of inhaled beclomethasone dipropionate or equivalent ). Topical steroids are allowed.
• Use of cytotoxic therapy in the previous 2 years.
• Plans to receive cytotoxic therapy during the study period.
• Concurrent moderate to severe illness. Need to defer vaccination until recovery. (Vaccination is not contraindicated in subjects with mild illnesses or with low-grade fever).