Table 2.
Subgroup analysis of SMS reminders effectiveness on improving childhood immunisation coverage
| Subgroup | No of studies* | Sample | Pooled RR | 95% CI | I2 statistic (%) | P value† |
| All studies | 19 | 32 712 | 1.16 | 1.10 to 1.21 | 90.4 | |
| Country’s income status | <0.001 | |||||
| Low-income country | 1 | 523 | 1.39 | 1.19 to 1.62 | – | |
| Lower middle-income country | 14 | 30 134 | 1.19 | 1.13 to 1.26 | 89.9 | |
| Upper middle-income country | 4 | 2055 | 1.01 | 0.96 to 1.06 | 58.4 | |
| Study design | 0.060 | |||||
| Randomized Controlled trials | 13 | 16 257 | 1.13 | 1.06 to 1.20 | 89.6 | |
| Non-randomised controlled trials | 6 | 16 455 | 1.22 | 1.12 to 1.32 | 92.2 | |
| Study setting | 0.625 | |||||
| Rural settings | 7 | 15 832 | 1.11 | 1.03 to 1.20 | 92.0 | |
| Mixed settings | 3 | 3060 | 1.22 | 0.99 to 1.51 | 96.7 | |
| Urban settings | 9 | 13 820 | 1.17 | 1.09 to 1.26 | 83.3 | |
| Outcome measured | 0.270 | |||||
| DPT-3 coverage | 8 | 4513 | 1.14 | 1.06 to 1.22 | 80.4 | |
| Overall immunisation coverage | 11 | 28 199 | 1.17 | 1.10 to 1.25 | 93.4 | |
| Number of SMS reminders sent | 0.441 | |||||
| 1 or 2 SMS reminders | 9 | 10 683 | 1.15 | 1.08 to 1.22 | 89.2 | |
| >2 SMS reminders | 10 | 22 029 | 1.17 | 1.07 to 1.27 | 92.0 | |
| Timing of last SMS reminder | 0.124 | |||||
| Sent on scheduled immunisation day | 4 | 5307 | 1.27 | 1.08 to 1.49 | 91.9 | |
| Sent 1 or 2 days before scheduled day | 15 | 27 405 | 1.13 | 1.07 to 1.19 | 89.9 | |
| Risk of bias (quality) of included studies | <0.001 | |||||
| Low risk of bias | 7 | 7625 | 1.38 | 1.22 to 1.55 | 86.7 | |
| Moderate and high risk of bias | 12 | 25 087 | 1.07 | 1.03 to 1.12 | 84.6 |
*Uddin et al, 2020 reported two separate interventions: Uddin, 2020 (A) for rural setting and Uddin 2020 (B) for urban setting.
†χ2 test for subgroup difference.
DPT-3, third dose of diphtheria, pertussis and tetanus; SMS, short message service.