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Externalities and Social Influence in Childhood Immunization

Development Challenge

Externalities play an important role in many health behaviors. Individuals frequently undervalue the social costs or benefits of their actions and underinvest in public goods like herd immunity. Prominent examples are deworming, smoking, open defecation and vaccination. To our knowledge, there is no field experiment that has tested for the effect of information about externalities on health behaviors; little is known about the effects of social influence and the role of social values in health decisions. This research aims to address important economic and health questions: What happens as people learn about externalities? Can we use social encouragements to improve the efficacy of the understanding of the externality? To what extent can individuals be motivated to internalize externalities through moral or social value primes? 


The vast majority of children in low-income areas of Karachi, Pakistan receive the first doses of routine immunizations but a significant share of children does not complete the recommended schedule. Clinic data from Korangi Town (a large industrial area and the study site of this project) shows that while 89% of caregivers vaccinate their child for the first vaccination BCG, only 40 percent of caregivers take their child for the final vaccination against Measles. As a result, immunization levels are below those required for herd immunity and regular mass immunization campaigns are necessary to avoid disease outbreaks. Qualitative interviews with caregivers show that most adults are unaware of the social dimensions of immunization. Caregivers think of childhood immunization as being beneficial only to the child that receives the vaccine. 

Evaluation Strategy

Researchers will implement a randomized field experiment in 160 communities in Korangi Town, Karachi. The aim of the study is to test if education about externalities and social influence can increase timely vaccination behavior among caregivers. The researchers will vary the way in which the externality information is presented i) by making it salient whether few or all caregivers in a community were informed about the social effects of immunization, and ii) by interacting the new information with a social value message. The hypothesis is that common knowledge of health externalities has a significant effect on people’s decision to act upon the externality information. By knowing that others received the same information, caregivers are more likely to be concerned that others might ask them if they vaccinated their child and hold them accountable for their (in)actions. A second hypothesis is that an appeal to social or moral values can facilitate other regarding behavior. Caregivers might feel a stronger moral obligation to vaccinate when primed by a social value that emphasizes the community-wide benefits of their actions.

Lady Health Workers, who are trusted members of the community, will provide the different information treatments. The research will be implemented in partnership with Interactive Research & Development (IRD).

Results and Policy Implications

Results forthcoming. 


Ongoing (2016-)