Influenza vaccination and warfarin anticoagulation: a comparison of subcutaneous and intramuscular routes of administration in elderly men.

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.