The effect of a combined influenza/pneumococcal immunization reminder letter

BACKGROUND: The effect of a combined influenza and pneumococcal immunization reminder letter on increasing influenza and pneumococcal immunization rates, and the timeliness of receiving immunizations after receipt of a reminder letter, have not been examined. This study addresses these issues using a sample of new Medicare beneficiaries residing in Hawaii. METHODS: Newly enrolled Medicare beneficiaries in Hawaii from 25 September 1995 through 31 August 1996 were randomly assigned to one of three groups: Group 1, no letter (n=2144); Group 2, influenza immunization reminder letter only (n=2213); or Group 3, pneumococcal and influenza immunization reminder letter (n=2171). Health Care Financing Administration claims data were compared among groups. RESULTS: In Group 3, the influenza immunization rate increased 3.8 percentage points (n=87; p=0.017) compared with Group 1. The Group 3 pneumococcal immunization rate increased 3.5 percentage points (n=78; p<0.001) compared to Group 1 and 4.0 percentage points (n=86; p<0.001) compared to Group 2. Sixty-six beneficiaries in Group 3 received simultaneous pneumococcal and influenza immunizations, a significant difference compared to Group 1 or Group 2. Increases in immunizations were observed immediately following the reminder letters and the effect persisted for 5 to 7 weeks. CONCLUSIONS: The combination letter increased both influenza and pneumococcal immunization rates and the simultaneous administration of immunizations without detrimental effect to influenza immunization rates. A combined reminder letter is inexpensive and recommended as part of a multicomponent campaign for adult immunization.