Faced with high rates of immunization drop-out, Uganda's immunization program requires innovative approaches to address this weakness. Building upon Uganda's growing mHealth infrastructure to pilot a scalable short message service (SMS) system to remind caregivers of their children's upcoming vaccination visits, it was hypothesized that the SMS intervention will increase immunization coverage in a cost-effective and affordable manner that would make it scalable. The study design was an investigator-blinded, multi-center, parallel groups randomized controlled trial with randomization occurring at the caregiver level in select health facilities of Arua District in Uganda. Enrollment took place at the time of Pentavalent 1 vaccination, and both arms included standard of care provided by the health worker. However, in the intervention arm, caregivers also received SMS text messages reminding them to return for their children's second and third doses of Pentavalent vaccine (four and eight weeks after the first dose of Pentavalent vaccine) and measles-containing vaccine (9 months of age). The primary outcome of interest is vaccination coverage at 12 months of age among children enrolled in the study and will be measured by comparing Penta3 and MCV coverage between arms. The study will also examine the SMS impact on timeliness of vaccine receipt, as it is hypothesized that those children receiving the SMS intervention will be more likely to have timely vaccination than those in the control group. The study will also assess caregiver acceptability and cost-effectiveness of the SMS intervention. In addition to assessing its impact on strengthening the immunization program, this intervention has implications for strengthening other programs of the health system through similar health messaging directed toward caregivers.

Inclusion Criteria:

• Is a caregiver of a child between the ages of 6 weeks and 6 months of age and presents at one of the study sites for child's Penta1 vaccination
• Access to a personal or household cell phone that can receive text messages
• Lives in Arua district

Exclusion Criteria:

• Does not have access to the cell phone number at time of registration
• Does not agree or is unable to consent to participate in the study
• Does not anticipate being the caregiver through the child's first birthday
• Plans to move out of Arua district in the upcoming year
• Prior enrollment of the caregiver with a different child