Mailed reminders for area-wide influenza immunization: a randomized controlled trial.

OBJECTIVE: To determine if mailed reminders would increase area-wide influenza immunization for persons aged 65 and older. DESIGN: A randomized, controlled trial. SETTING: Ten counties in Indiana. PARTICIPANTS: Using a Medicare database, 10,000 subjects were selected randomly from 10 counties in Indiana and randomized for the study. Using pre-established criteria, 4503 persons in the control group and 4508 in the intervention group were eligible for study. INTERVENTION: Intervention subjects received mailed reminders during the immunization season of 1995. MEASUREMENTS: Data from mailed surveys, Medicare claims, and phone calls were used to determine immunization rates. RESULTS: Of those surveyed who received immunization, only 63.4% filed a Medicare claim. Immunization rates were high in both groups but higher in the intervention group, 69.0% versus 64.2%. Age, presence of lung disease, assignment to the intervention group, presence of heart disease, and an age-sex interaction term were significantly and independently related to immunization. CONCLUSIONS: The Healthy People Year 2000 goal (60% immunization for persons 65 and older) was exceeded in this population. Medicare claims data do not reflect immunization rates accurately. Mailed reminders, an inexpensive intervention, increased immunization rates area-wide and have potential for cost savings.