Objective: To evaluate the incremental effect of a second client reminder postcard or an influenza tool kit targeted toward employers on increasing influenza vaccination rates among adults age < 65 years at high risk for complications from influenza illness.
Methods: In this demonstration study, enrollees of 3 managed care organizations (n = 8881) were randomized at the employer level into 4 arms: 1 postcard, 2 postcards, 1 postcard + tool kit, and 2 postcards + tool kit. The postcards and tool kits were mailed during the fall of 2001, and their effect on influenza vaccination rates was assessed through a survey.
Results: Compared with a single postcard, 2 postcards increased vaccination rates by 4 percentage points (adjusted relative risk = 1.05; P < .05) among persons aged 50 to 64 years but did not have any effect among younger adults. Older adults had a greater burden of disease and reported more favorable knowledge and attitudes toward the influenza vaccine. The influenza tool kit did not appear to have any incremental effect on vaccination rates.
Conclusions: Our findings underscore the necessity of evaluating the effectiveness of interventions in different population subgroups and of identifying factors that modify the effectiveness of interventions. Rigorous assessment of intervention effectiveness in managed care settings will enable decision makers to optimize use of scarce healthcare dollars for improving the health and well-being of enrollees.