Haji 2016.

Study characteristics
Methods	Aim: to assess the impact of SMS and sticker reminders to reduce dropout rates for routine childhood vaccinations, and determined factors associated with missed vaccination in selected districts in Kenya. Study design: cluster RCT Recruitment: children aged < 12 months who were brought to the selected vaccinating health facilities in the 3 districts for their first dose of pentavalent vaccine were recruited on a first‐come basis until the strategy‐level target sample sizes was reached. Study duration: 8 weeks Study dates: February 2014 to December 2014 (enrolment ceased October 2014)
Participants	Inclusion criteria: children aged < 12 months attending for first dose of pentavalent vaccine Sample size: 1116 (SMS: 372 participants, 3 clusters; targeted non‐digital communication (stickers): 372 participants, 3 clusters; usual care: 372 participants, 3 clusters) Age (mean): carers: 26 (range 14–45) years Sex (male): infants = 51% Country: Kenya (lower middle‐income) Setting: community‐based, linked to 9 vaccinating health facilities in 3 districts (Machakos, Langata, and Njoro), 3 facilities in each district
Interventions	Intervention: SMS reminders sent from an automated web‐based system in Kiswahili and English, sent 2 days before (reminding the date of next vaccine and which health facility to attend) and on the day of the scheduled vaccination for the second and third doses of pentavalent vaccine. Content: SMS reminders Frequency and intensity: 4 reminders (2 days before and on day of both second and third dose), reminders were at 10 weeks (–2 days) until 14 weeks Control: 1. standard care/no intervention. 2. targeted non‐digital communication: reminder sticker Co‐interventions: scheduled vaccination due date was indicated on the child's health booklet as per routine procedures. All groups received routine health education and advice on vaccination.
Outcomes	1. Receipt of pentavalent vaccine (at 10 and 14 weeks of age); 2. Costs Outcomes reported but not included in the review: 1. Mean days delay in receiving vaccine doses (at 10 and 14 weeks of age) (outcome not eligible for inclusion); 2. Factors associated with missed vaccination (not included in review, results were not reported per group; 3. Did not return for vaccinations (not included in review, those receiving vaccinations were extracted) Outcome assessment time point: 10 and 14 weeks of age corresponding to the second and third doses of the pentavalent vaccine
Funding/declarations of interest	Funding: US Center for Disease Control and Prevention Conflicts of interest: authors declared no competing interests.
Notes	Districts were selected that had > 10% dropout rate for third dose of pentavalent vaccine. Trial ID: not reported Cluster features: 9 health facilities were randomised. Mean cluster size: 124. The study did not adjust for clustering effect for any of the relevant outcomes; we used ICC 0.0487 (derived from k = 0.089 reported in Gibson 2017) to adjust for cluster effect in the analyses.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "We selected three health facilities in each district, and randomly allocated each facility …" Comment: no further details reported.
Allocation concealment (selection bias)	Unclear risk	No information on allocation concealment.
Selective cluster recruitment	High risk	Convenient enrolment of participants likely to have taken place after cluster allocation to intervention arms. Quote: "We selected three health facilities in each district, and randomly allocated each facility to one of the two interventions … or to serve as the control group … Participants were conveniently enrolled in the selected health facilities until the strategy‐level target sample sizes were reached."
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not possible to blind; participants and personnel were aware of cluster allocations for data collection purposes.
Blinding of objective outcome assessment (detection bias)	High risk	Personnel were aware of cluster allocations for data collection purposes.
Blinding of subjective outcome assessment (detection bias)	High risk	Self‐reported measures were at high risk of detection bias since the study was not blinded.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Flow of participants and clusters through the study was not clearly reported.
Selective reporting (reporting bias)	Low risk	Outcomes are reported exhaustively, including for acknowledged limitations.
Other bias	High risk	Contamination: acknowledged limitation was that (quote) "If a care giver took the child to another facility for second or third pentavalent dose, the system considered the child unvaccinated." Follow‐up phone‐calls determined that 35 infants had been taken to other centres. Baseline differences: there were no statistical differences in demographic characteristics among carers and children enrolled in each of the 3 groups.