Influenza Vaccination and Warfarin Anticoagulation: A Comparison of Subcutaneous and Intramuscular Routes of Administration in Elderly Men

Abstract

Study Objectives. To determine if subcutaneous administration of influenza vaccine is as immunogenic as the intramuscular route, and to evaluate the frequency of local adverse events associated with both routes in elderly anticoagulated men.Design. Single‐blind, prospective study of consecutively enrolled subjects.Setting. Ambulatory clinic at a university‐affiliated Veterans Affairs medical center.Patients. Twenty‐six men age 60 years or older, receiving therapeutic dosages of warfarin.Interventions. Subjects were randomized to receive either intramuscular or subcutaneous injection of a standard trivalent influenza vaccine.Measurements and Main Results. Serum antibody titers to the vaccine's components were measured at baseline, and 6 weeks and 4 months after vaccination. Both routes of administration induced comparable serum antibody titers. There were no differences in adverse events at administration sites between routes of administration.Conclusions. Elderly individuals are able to mount an immune response to influenza vaccine and produce antibody concentrations deemed protective. The routes of administration are similarly effective at inducing an immune response. The intramuscular route in anticoagulated elderly men does not commonly result in local bleeding complications.