1.1 Background of the study

Missed and delayed childhood vaccinations remain a major public-health problem in many low- and middle-income countries because they increase the risk of outbreaks of vaccine-preventable diseases. Mobile-phone reminder systems — including SMS/text messages, automated voice calls, and bidirectional messaging — are attractive interventions because they are comparatively low-cost, widely scalable and can deliver timely appointment prompts and brief education directly to caregivers. Systematic reviews and meta-analyses indicate that text-message reminders produce modest but consistent improvements in vaccination uptake and timeliness, and that interventions combining reminders with tailored educational content or two-way communication often achieve larger effects than one-way reminders alone (Louw et al., 2024; Currie et al., 2024). Randomised trials from LMIC settings demonstrate that well-designed mobile reminders can increase on-time receipt and series completion for routine childhood vaccines when implemented with good fidelity; however, the magnitude of effect is context-dependent. Key implementation challenges include stable phone ownership and contact details, caregiver literacy and language preferences, mobile-network reliability, message timing and content, and integration with facility scheduling and defaulter-tracing systems (Mekonnen et al., 2021; Yunusa et al., 2024). Because these factors vary across settings, local evaluations that combine effectiveness and implementation metrics are needed to inform scale-up decisions and to tailor reminder design to population needs. Kano Municipal LGA is densely populated and linguistically diverse, with documented micro-level gaps in timeliness and completion of routine immunizations in certain wards. Given relatively high mobile-phone penetration in urban Nigeria but also frequent phone-number turnover in lower-income households, an LGA-level pragmatic evaluation is warranted to measure both the effect on vaccination outcomes and the real-world implementation challenges (delivery rates, language preferences, number churn) that program managers must address before scaling reminders across Kano (Louw et al., 2024; Yunusa et al., 2024).

1.2 Statement of the problem

While routine immunization programmes in Kano State have achieved important gains, clinic reports and supervisory data reveal persistent missed appointments and drop-outs between initial and later doses, particularly for vaccines scheduled later in infancy. Mobile reminders have proven beneficial in other LMIC contexts, but programme managers in Kano Municipal lack locally specific evidence about expected effect sizes, equity effects (which caregiver subgroups benefit most), and operational constraints (message delivery, language/literacy mismatches, phone-number churn and platform costs). Without such evidence, investments risk being poorly targeted — for example, deploying one-way SMS in low-literacy areas where voice calls or community follow-up would be more effective — or underestimating resources needed for sustainable scale-up (Mekonnen et al., 2021; Currie et al., 2024).

A pragmatic, cluster-randomised evaluation that measures both immunization outcomes and implementation metrics (message delivery success, caregiver receipt/response, phone-number stability, and cost per additional fully immunized child) will therefore provide the actionable evidence Kano Municipal needs to design a cost-effective, equitable reminder programme.

1.3 Aim and Objectives of the Study

Aim: To evaluate the effectiveness and implementation fidelity of a mobile-phone reminder system for improving completion and timeliness of routine childhood vaccinations among caregivers in Kano Municipal LGA, Kano State.

Specific objectives:

1. Compare the proportion of children who complete the age-appropriate routine immunization schedule (by 12 months) between caregivers receiving mobile reminders and those receiving usual care.
2. Compare vaccine-specific timeliness (on-time receipt within target windows) between intervention and control groups.
3. Describe implementation metrics: message delivery rates, language used, caregiver receipt/reading rates, proportion of caregivers who respond (if two-way), and phone-number churn.
4. Assess differential effects by caregiver subgroups (maternal age, education level, parity, household socioeconomic status).
5. Estimate incremental program cost per additional fully immunized child attributable to the intervention.
6. Document caregiver acceptability and perceived barriers or facilitators to the reminder system through qualitative interviews.

1.4 Research Questions

1. Does a mobile-phone reminder intervention increase the proportion of infants who complete the routine immunization schedule by 12 months in Kano Municipal LGA?
2. Does the intervention improve timeliness of scheduled vaccine doses compared with usual care?
3. Which caregiver or household subgroups show the greatest benefit from the reminder system?
4. What operational challenges (failed message deliveries, wrong numbers, language or literacy mismatches) limit the intervention’s effectiveness, and how frequently do they occur?
5. What is the incremental cost per additional fully immunized child produced by the reminder strategy in this context?

1.5 Scope of the Study

Design: Pragmatic, parallel-arm cluster-randomised controlled trial with clusters defined as primary health facility catchment areas. The trial will include an embedded process evaluation and a basic cost-effectiveness (incremental cost per additional fully immunized child) analysis.

Setting: Kano Municipal Local Government Area, Kano State.

Population: Caregivers of newborns/infants registered for routine immunization at participating PHC facilities who have access to a mobile phone (their own or a household member’s) and who consent to receive reminders. Infants must be resident in the catchment area and expected to remain for at least 12 months.

Intervention: Automated mobile reminders (SMS and/or automated voice calls according to caregiver preference) sent before scheduled immunization appointments and a brief follow-up reminder if the appointment is missed. Messages will be offered in Hausa and English and will be piloted for clarity and acceptability. A two-way response option will be available in a subset of clusters to explore feasibility and added value.

Comparison: Usual care (appointment cards and standard community mobilisation, without automated phone reminders).

Primary outcome: Proportion of infants who have received all age-appropriate routine vaccine doses by 12 months of age (verified by immunization card or facility records).

Secondary outcomes: On-time receipt of scheduled doses, drop-out rates between early and later doses, message delivery and read/response rates, phone-number churn rate, caregiver acceptability, and incremental cost per additional fully immunized child.

Methods summary: Cluster randomisation at facility catchment level; sample size calculation to detect a pre-specified absolute increase in full immunization (e.g., from 60% to 72%, finalised after baseline assessment); data collection by immunization register review and caregiver follow-up; implementation metrics from the SMS/IVR platform logs; qualitative interviews with a purposive sample of caregivers and facility staff to explore barriers and facilitators.

Ethics & dissemination: Ethical approval will be sought from an accredited IRB and Kano State health authorities; written informed consent will be obtained from caregivers. Results will be shared with Kano State Expanded Programme on Immunization (EPI) managers, LGA health teams and published in peer-reviewed journals.

References

Currie, G., McLeod, C., Waddington, C., & Snelling, T. L. (2024). SMS-based interventions for improving child and adolescent vaccine coverage and timeliness: A systematic review. BMC Public Health, 24, 1753.

Louw, G. E., Hohlfeld, A.-S. J., Kalan, R., & Engel, M. E. (2024). Mobile phone text message reminders to improve vaccination uptake: A systematic review and meta-analysis. Vaccines, 12(10), 1151.

Mekonnen, Z. A., Gelaye, K. A., Were, M., & Tilahun, B. (2021). Effect of mobile phone text message reminders on the completion and timely receipt of routine childhood vaccinations: A superiority randomized controlled trial in Northwest Ethiopia. JMIR mHealth and uHealth, 9(6), e27603.

Yunusa, U., Ladan, M. A., Ibrahim, A. H., & Gomaa, H. E. M. (2024). Utilization of mobile reminders in improving the completeness and timeliness of routine childhood immunization in Kano Metropolis, Nigeria: A randomized controlled trial. Journal of Pediatric Health Care, 38(5), 727–736.