All enrolled caregivers will receive a congratulatory text message at enrollment which indicates who is conducting the study and which also includes a general-health related saying, "The greatest wealth is health". No additional text messages or travel subsidies will be sent to caregivers randomized to the control arm.

At enrollment, participants will be told to expect 2 SMS reminders for measles vaccine; first, at 3 days before and second, on the day before the scheduled measles vaccine at 9 months of age. At most, enrolled caregivers will receive three text messages (two for the measles vaccine and one for welcoming mother to the study). Text messages will be sent in English, Kiswahili or Dholuo language, according to the mother's preference. These reminders will have information about the child's scheduled immunization date.

Participants will receive SMS reminders as described in the SMS reminder arm. Additionally, participants will be sent a 150 Kenyan Shillings (KES) incentive to the mobile phone number they provided at enrollment. The incentive will be delivered three days before the child turns nine months (i.e. sent on the same day as the first SMS reminder). Caregivers will receive the mobile-money incentive unconditionally. The intent of the incentive is to help offset the costs associated with transportation to the clinic. The transaction costs associated with mobile-money transactions will be borne by the study such that mothers will receive the full 150 KES.

Caregivers will receive two text message reminders for their child's measles immunization scheduled for 9 months of age

Proportion of children receiving measles vaccination by 10 months of age by study arm

As a secondary analysis of the primary outcome, time-to-measles immunization curves will be constructed using the Kaplan-Meier method and study arms will be compared using the Cox model. The 25th, 50th, and 75th percentiles for time to immunization and the number of days delayed, in relation to the measles due date, will also be reported for each vaccine and by study arm.