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J Gen Intern Med. 1998 Jul;13(7):469-75.

Influenza immunization in a managed care organization.

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Center for Clinical Effectiveness, Henry Ford Health System, Detroit, Mich 48202, USA.



To compare the effects of different types of computer-generated, mailed reminders on the rate of influenza immunization and to analyze the relative cost-effectiveness of the reminders.


Randomized controlled trial.


Multispecialty group practice.


We studied 24,743 high-risk adult patients aligned with a primary care physician.


Patients were randomized to one of four interventions: (1) no reminder, which served as control; (2) a generic postcard; (3) a personalized postcard from their physician; and (4) a personalized letter from their physician, tailored to their health risk.


The immunization rate was measured using billing data. A telephone survey was conducted in a subgroup of patients to measure reactions to the mailed reminders. To evaluate the cost-effectiveness, a model was constructed that integrated the observed effect of the interventions with published data on the effect of immunization on future inpatient health care costs.


All three of the reminders studied increased the influenza vaccination rate when compared with the control group. The vaccination rate was 40.6% in the control group, 43.5% in the generic postcard group, 44.7% in the personalized postcard group, and 45.2% in the tailored letter group. The rates of immunization increased as the intensity of the intervention increased (p < .0001). Seventy-eight percent of patients in the letter group deemed the intervention useful, and 86% reported that they would like to get reminders in the future. The cost-effectiveness analysis estimated that in a nonepidemic year, the net savings per 100 reminders sent would be $659 for the personalized postcard intervention and $735 for the tailored letter intervention. When these net cost-savings rates were each applied to the entire high-risk cohort of 24,743 patients, the estimated total net savings was $162,940 for the postcard and $181,858 for the tailored letter.


Although the absolute increase in immunization rates with the use of reminders appeared small, the increases translated into substantial cost savings when applied to a large high-risk population. Personalized reminders were somewhat more effective in increasing immunization, and personalized letters tailored to the patients' condition were deemed useful and important by the individuals who received them and had a beneficial indirect effect on patient satisfaction.

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