Can unvaccinated children be reached through mobile phones? Analyses of national cross-sectional surveys from 70 countries.

Background: Interventions using mobile phones, otherwise known as mHealth interventions, are increasingly being used in low- and middle-income countries to remind families about scheduled child immunisations. Despite this, few studies examined impact on zero-dose children - those who failed to receive a single dose of a routine vaccine. As disparities in mobile phone ownership may limit the effectiveness of mHealth interventions, we assessed associations between mobile phone ownership, gender, wealth, residence, and zero-dose and modelled their potential impact for reaching unvaccinated children. Methods: We analysed 70 nationally representative surveys with data on immunisations and mobile phone ownership by households and mothers, and correlated ownership with household wealth and place of residence. We performed analyses at the individual child level and pooled across all countries weighted by national populations. We modelled the mHealth interventions' potential impact on zero-dose prevalence by estimating how many unvaccinated children are reachable via mobile phones. Results: The surveys included 163 527 children aged 12-23 months, with 13.4% being zero-dose. Among them, 34% of mothers and 73% of households had a mobile phone, compared to 60% and 89% for vaccinated children. Mobile phone ownership by mothers ranged from 32% in the poorest to 86% in the wealthiest quintile. A hypothetical 100% effective intervention using household mobile phones would reduce zero-dose prevalence from 13% to 4%, while one using similar effectiveness assumptions for mothers' phones would reduce national prevalence to 10%. Interventions with effectiveness ranging from 10% to 50% would lead to smaller impact levels. The largest impact is expected in countries like Guinea and Cote d'Ivoire, where both zero-dose prevalence and mobile phone ownership are high. Conclusions: The potential impact of mHealth interventions for reaching zero-dose children may be limited by mobile phone ownership among mothers and families, particularly among the poor, where we find the greatest number of unvaccinated children.