Impact of a patient reminder letter from their general practitioners on influenza vaccination: A quasi-experimental study in Paris, France

BACKGROUND: Seasonal influenza vaccination coverage levels remain too low in many countries. OBJECTIVES: This study aimed to evaluate the impact of a reminder letter from their general practitioner (GP) on patients’ influenza vaccination. METHODS: Eligible patients for this controlled non-randomised study were the vulnerable categories targeted by the 2019–2020 national health insurance fund (NHIF) vaccination campaign, on the lists of 14 GPs from three practices in Paris (France) and unvaccinated on January 2, 2020 (mid-campaign). The choice of practices and assigning five GPs to the intervention arm were made for convenience. At mid-campaign, GPs in the intervention arm sent a standardised letter reminding each eligible patient to be vaccinated. In the control arm, GPs worked as usual. The intervention effect, calculated from the NHIF databases, was estimated by the difference between the groups in their vaccination coverage at the end of the campaign, with a linear mixed model adjusted for age, sex, chronic disease (at the patient level) and medical practice (at the GP level). RESULTS: The vaccination coverage at the end of the campaign was 14.7% in the intervention group (n = 317) and 1.7% in the control group (n = 493): a difference of 13.1% points (95% confidence interval [9.0–17.2], number needed to send 7.7). At the campaign’s end, vaccination coverage among patients from the lists of GPs in the intervention arm was 62.7%, and 46.2% among patients from the control-arm GP lists. CONCLUSION: Reminder letters could help increase influenza vaccination coverage.