Short Message Service (SMS) Reminders for Childhood Immunisation in Low-Income and Middle-Income Countries: A Systematic Review and Meta-Analysis

"It is reasonable that in resource-constrained settings, simple and cost-effective mHealth interventions such as SMS reminders should be implemented in the healthcare system to improve child health outcomes."

Childhood immunisations are often delayed or missed due to caregivers' lack of awareness about the vaccines or their due dates. Many low- and middle-income countries (LMICs) do not have functioning primary healthcare systems and routine well childcare services, making a somewhat complicated primary childhood vaccine series (with multiple appointments at various ages) difficult for caregivers to remember. Immunisation reminders have been shown to improve compliance and timeliness, with mobile phone reminders found to have promise. In light of the increasing ubiquitousness of mobile phones in LMICs, this study evaluated the effectiveness of short message service (SMS) reminders in improving immunisation coverage and timeliness in LMICs.

The researchers systematically searched for randomised controlled trials (RCTs) and non-RCTs of the effects of mobile phone SMS reminders on childhood immunisation published from January 1 2000 to December 31 2020 in 135 World-Bank-defined LMICs. In the end, 18 studies met the inclusion criteria for data extraction, qualitative synthesis, and meta-analysis. The studies, 13 of which were RCTs, were undertaken in 11 different LMICs.

Twelve studies showed that SMS reminders significantly improved childhood immunisation coverage in children in the intervention group compared with those in the control group with usual care. The researchers found no difference in effects by study setting, outcome measure, number of SMS reminders sent, or the timing of the SMS reminder. While SMS reminders were marginally effective in upper-middle-income countries, they were significantly more effective in lower-middle-income and low-income countries. (Upper middle-income countries are likely to have high vaccination rates and thus limited potential for SMS reminders to improve the childhood immunisation rates further - i.e., the ceiling effect.)

Of the 12 included studies that evaluated the effect of SMS reminders on childhood immunisation timeliness, 10 of them demonstrated that SMS reminders significantly improve timely receipt of vaccines in children in the intervention group compared with those in the control group with usual care. The timely receipt of childhood vaccines was significantly improved when more than two SMS reminders were sent for childhood immunisation appointment versus when one or two SMS reminders were sent, and this difference was statistically significant. These findings suggests that habituation - the propensity to ignore messages because of high frequency - is not a problem and that a reminder sent at least 24 hours before the scheduled immunisation day allows sufficient time for the mother/caregiver to prepare for the appointment. The effectiveness of SMS reminders in improving timely childhood vaccination was consistent across income status, indicating the value for this intervention across multiple settings.

"Although this study demonstrated that SMS reminder is an effective tool for increasing vaccination uptake and timeliness in LMICs, a number of critical factors highlighted from included studies must be considered before implementing this intervention." For instance:

• Rural settings have higher proportion of families sharing a single phone than urban settings, which makes it difficult to know if the message is going to the right person. Relatedly, mobile phone interventions require extensive infrastructure for mobile communication and mothers to have the facilities for charging their phones, which might not always be the case, especially in rural communities.
• SMS reminders depend on mothers being able to read SMS messages. "Given that several studies have demonstrated mothers' preference for phone call reminders over SMS reminders, particularly in populations with low literacy and resource-constrained settings,...it is important to further explore in future studies if and how SMS reminders can be combined with mobile phone reminders (multiple modes of reminders) to obtain optimal outcomes."
• Forgetting vaccination appointment or ignoring child vaccination schedules are often not the main hurdle to accessing care. SMS reminders do not help address challenges such as accessibility (transportation, transport costs), attitude of healthcare workers, availability of vaccines, awareness of the importance of vaccination, and outright rejection of vaccination.
• More qualitative studies are needed to understand nuanced social and cultural details, such as the optimal number of reminders, ideal time for sending reminders, and content of reminder message for operational optimisation of SMS reminders.

Even though the included studies showed substantial heterogeneity, the findings imply that SMS reminders could be effective in improving childhood immunisation coverage and timeliness in children less than 2 years in LMICs. This is especially significant in lower-middle-income and low-income countries, where the highest numbers of unvaccinated children live, and children are most likely to miss out on lifesaving vaccines.