Evaluation of the impact of different notification methods for unvaccinated individuals in a ACWY meningococcal vaccination campaign.

INTRODUCTION

Invasive meningococcal disease (IMD) in Spain remains rare, yet rising trends in serogroups W and Y prior to 2019 prompted the national recommendation to replace adolescent meningococcal C vaccination with the quadrivalent meningococcal ACWY (MenACWY) vaccine and to implement a catch-up campaign for individuals born between 2001 and 2007. In the Region of Murcia, the COVID-19 pandemic delayed implementation until September 2021. After an initial mass-vaccination phase and a long period without active outreach, coverage remained suboptimal, prompting a multi-phase reminder strategy. This study assessed the impact of different reminder combinations-postal letters, short message service (SMS), or both-on MenACWY vaccination coverage.

METHODS

A randomized interventional study was conducted between September and October 2022 among 66,891 unvaccinated individuals. Participants were allocated into four groups based on birth month, each receiving a different reminder strategy: letter followed by SMS, simultaneous letter and SMS, SMS followed by letter, or delayed combined reminders. Coverage was analysed overall and by age group, sex, and intervention arm.

RESULTS

Six weeks after the first intervention, coverage increased from 53.52% to 56.40%. After the second intervention, coverage rose to 59.98% at six weeks and 61.07% at twelve weeks-a total increase of 7.55 percentage points. Significant differences were observed across the four strategies (p < 0.001). The most effective approach was sending a postal letter followed by an SMS six weeks later, which consistently produced the highest coverage. No differences were found by sex. Coverage achieved was significantly higher among minors (<18 years) than adults (22.5% vs. 13.2%, p < 0.001). Beyond 12 weeks after each intervention, additional increases were minimal (<1%).

CONCLUSIONS

This study demonstrates that sequential reminders-specifically a postal letter reinforced by an SMS-substantially improve adolescent and young adult vaccination uptake. These findings support the integration of combined reminder strategies into routine catch-up vaccination programs.