Social Signaling and Childhood Immunization: A Field Experiment in Sierra Leone

This paper explores the use of social signaling as a policy tool to sustainably a˙ect childhood immunization. In a 26-month field experiment with public clinics in Sierra Leone, I introduce a verifiable signal – in the form of color-coded bracelets – given to children upon timely completion of the first four, or all five required vac-cinations. Signals increase parents’ belief in the visibility of their actions and their knowledge of other children’s vaccine status. The impact of signals varies signifi-cantly with the cost and perceived benefits of the action: there are no discernible e˙ects on timely and complete immunization when the signal is linked to an easier-to-complete vaccine with low perceived benefits, and large, positive e˙ects when the signal is linked to a costlier-to-achieve vaccine with high perceived benefits. Parents adjust their behavior nine months prior to realizing the social image bene-fit, demonstrating the motivational strength of signaling incentives. Of substantive policy importance, bracelets increase full immunization at one year of age by 9 per-centage points, with impacts persisting up to two years. At a cost of US$24.7 per additional fully immunized child, social signals can prove more cost-e˙ective than financial or in-kind incentives.