Enhancing influenza immunization. Postcard and telephone reminders and the challenge of immunization site shift

OBJECTIVE: To determine if postcard and telephone reminders increased the rate of influenza immunization of Medicare beneficiaries. DESIGN: Before and after trial (postcard reminders) with systematically allocated control group (telephone reminder intervention). SETTING: A semirural family practice residency program. PATIENTS AND OTHER PARTICIPANTS: All 475 noninstitutionalized persons older than 65 years who had received at least 1 office service in the previous 2 years. INTERVENTION: In September 1996, each of 475 patients received a postcard urging prompt influenza immunization. Those not responding within 1 month were systematically allocated either to a group receiving further telephone contact or to a control group. At the time of telephone contact, any offered information about influenza immunization received outside the Smoky Hill Family Practice Center, Salina, Kan, was recorded. MAIN OUTCOME MEASURES: We measured the percentage of change in practice-administered influenza immunizations compared with the baseline rate of the preceding 2 years; the difference in immunization rates between the telephone intervention group and controls; and the number of patients contacted by telephone who reported receiving influenza immunization at a site other than the Family Practice Center. RESULTS: Twenty-eight percent of patients who received a postcard obtained office influenza immunizations within 1 month, but no additional immunizations could be attributed to the telephone intervention. Thirty-five percent of patients contacted by telephone reported receiving influenza immunization at a site other than the Family Practice Center. CONCLUSIONS: The postcard intervention was associated with a significant increase in the office immunization rate. This increase may have been confounded by "site shift" in which individuals came to the office for an immunization that they might otherwise have received at other community sites.