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Table 2 Characteristics of included studies
| S. no | Author (year) | Country | Study design | Study participants/setting | Population (I, C) | Interventions/control | Follow-up periods | Outcome measure | Event among intervention | Event among control |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Bangure et al. (2013) | Zimbabwe | RCT | Women who delivered were recruited into the study at 4 Kadoma city clinics in Mashonal and West province of Zimbabwe | 304 (152, 152) | SMS reminders were sent at 6, 10, and 14 weeks on 7, 3, and 1 day before vaccination due dates. Control group received routine care. | 14 weeks | Immunization coverage at 6, 10, and 14 weeks | 144/152 | 114/152 |
| 2 | Schmidt et al. (2012) | USA | RCT | Parents of newborns being discharged from a local hospital who intended to seek child health care at the university-sponsored pediatric resident and faculty clinic | 68 (28, 40) | A text message reminder sent 7 days prior to vaccination schedules. Control group received standard notifications. | 7 months | Receipt of vaccinations due at 2, 4, 6 months of age | 22/28 | 31/40 |
| 3 | Dini et al. (2000) | USA | RCT | Households in the Denver metropolitan area whose children had received the first dose of DTP and/or poliovirus vaccines | 960 (440, 520) | Reminder messages sent on due dates of vaccination. Control group has no notifications. | 24 months | Vaccination series completion at 24 months of age | 217/440 | 213/520 |
| 4 | Haji et al. (2014) | Kenya | RCT | Children < 12 months of age who were brought to the selected vaccinating health facilities in the three districts of Machakos, Langata and Njoro for their first dose of pentavalent vaccine | 744 (372, 372) | Text reminders sent 2 days before and on the day of the scheduled Vaccination due date. Control group received routine reminder. | 14 weeks | Receipt of scheduled vaccines at 10 and 14 weeks | 359/372 | 309/372 |
| 5 | Eze GU et al. (2015) | Nigeria | Parallel group RCT | Paired child-caregivers were followed-up at 8 health facilities in an urban/sub-urban area in South Nigeria | 905 (452, 453) | A text message reminder sent a day before the due date. Control group received routine care. | 18 weeks | DPT3 Coverage at 18 weeks | 312/452 | 273/453 |
| 6 | Niederhauser et al. (2015) | USA | RCT | The study enrolled parent/infant dyads recruited from a large federally qualified health center, a Women, Infants and Children clinic, a private pediatric clinic and at the Honolulu Baby Expo | 42 (19, 23) | Text message sent 4 weeks and 2 weeks prior to the due date for the infant’s 2, 4, and 6-month vaccinations. Control group received routine care. | 7 months | 5 vaccines (DTaP, HepB, HIB, PCV, and polio) complete coverage at specific ages by group | 7/19 | 15/23 |
| 7 | Domek et al. (2016) | Guatemala | Pilot RCT | Infants aged 8–14 weeks presenting for the first dose of the primary immunization series at two public health clinics were enrolled | 321 (160, 161) | SMS text messages at 6, 4, and 2 days before the next scheduled date for visits 2 and 3. | 7 months | Completing all (pentavalent, pneumococcal, polio, and rotavirus) vaccines | 130/160 | 122/161 |
| 8 | Gibson et al. (2017) | Kenya | Clustered RCT | Villages were randomly and evenly allocated. Caregivers were eligible if they had a child younger than 5 weeks who had not yet received a first dose of pentavalent vaccine | 748 (388, 360) | SMS reminders sent 3 days and the day before vaccination visits at 6, 10, and 14 weeks and at 9 months. Control group with no SMS service. | 12 months | Full coverage (BCG, three doses of polio, three doses of pentavalent and measles) | 332/388 | 296/360 |
| 9 | Hofstetter et al. (2015) | USA | RCT | Parents of 9.5–10.5-month-old children from four urban academically affiliated pediatric clinics | 1368 (686, 682) | Text reminder sent 2 days before the schedule. Control arm with usual care. | 13 months | MMR vaccination by 13 months | 263/686 | 270/682 |
| 10 | Stockwell et al. (2012) | USA | RCT | Four community-based clinics in the USA | 5165 (2576, 2589) | Text message reminders sent a month before due date. Control received usual care. | 12 months | Receipt of an influenza vaccine | 1316/2576 | 1202/2589 |
