Background: We reviewed published and unpublished studies of mass mailings designed to increase utilization of influenza vaccine among Medicare beneficiaries.
Methods: Search of computerized indexes for published studies and the Medicare Peer Review Organization Health Care Quality Improvement Project database for unpublished studies. Study selection criteria were: use of a controlled trial design and use of mass mailings direct to Medicare beneficiaries to increase receipt of influenza vaccinations. Study selection and data extraction were performed in duplicate by physician reviewers with consensus resolution.
Results: Six controlled trials of mass mailings were identified. One study, published in the Morbidity and Mortality Weekly Report (MMWR), reported a modest but statistically significant improvement in influenza vaccination rates among patients who received a letter relative to those who did not. This study was cited as justification for mail interventions performed in five subsequent studies, none of which reported clinically meaningful results. None of these five studies was published.
Conclusions: Mass mailings have at best had clinically trivial effects on increasing influenza vaccination among Medicare beneficiaries. Publication bias has contributed to continued use of a relatively ineffective intervention.