Completion of routine immunization for infants has been a challenge in Nigeria, and existing strategies implemented to promote immunization coverage yielded limited success. The use of reminder short services message (SMS) in mobilizing mothers of infants, especially in rural areas with lower immunization coverage has been suggested. This study investigated the effect of reminder SMS sent to mothers in rural communities on full and timely completion of routine childhood immunization. A quasi-experimental design was adopted, 3500 mothers of infants were categorized into the Intervention and Control groups recruited at various Primary Healthcare Centres in 6 states and the FCT, Nigeria. Reminder SMS were sent to mothers in the intervention group for 10 months. We adopted mixed methods of data collection, significance level set at p = 0.05. Majority of respondents were married (Control 94.3%; Intervention 95.5%), have experienced multiple births (Control 79.0%; Intervention 74.9%). Adherence to routine immunization appointment dates and completion of all immunizations was higher in the Intervention group (76.0%) compared with the Control (73.3%). A significant association between adherence to appointment dates and completeness of routine immunization vaccine was found. The Intervention group had a significantly higher completion rate for measles and yellow fever vaccines (55.3%; 75.9%) compared with the Control group (26.8%; 23.9%). Qualitative findings revealed positive comments from mothers in the intervention group that the messages increase awareness of immunization dates, assisted in readjusting their time which influenced timely completion. Interventions using reminder SMS enhanced infant immunization delivery; we recommend scale-up and integration into the health system to increase national immunization coverage.

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