Widespread immunization has transformed public health in recent decades. Vaccines are a highly effective and inexpensive way to save children’s lives; they have prevented an estimated 150 million deaths over the last fifty years. Yet despite this progress, 14.5 million children globally went without vaccinations in 2023, and over two million children die each year from vaccine-preventable diseases.

Boosting immunization coverage requires a tailored approach. There are many reasons why a child might miss life-saving vaccines—health systems might not be working for local communities, and families might be hesitant or might not have the means to get their children vaccinated.

If clinics are far away, bringing vaccines closer to families can boost coverage. Local, temporary (or mobile) immunization “camps” in rural villages can make it easier for families to access vaccines. In India, for example, a randomized evaluation found that immunization camps had a large impact on improving vaccine coverage, compared to relying on local public health clinics that were harder to access. The immunization camps were reliable and accompanied by vaccine education from a social worker, whereas public health clinics often had absent staff.

In places where vaccination rates are low and health workers are not doing their jobs, programs that improve workers’ job performance can boost coverage. In Pakistan, for example, community health workers administered more polio vaccines when their supervisors monitored their activities via smartphone, and the workers received cash for performing better. Results of randomized evaluations show that monitoring programs may be more effective in contexts where vaccine coverage is particularly low.

If vaccines are readily available but vaccination rates are still low, programs that help increase families’ demand for vaccines can boost coverage. Families may still have trouble vaccinating their children for a range of reasons, including not being able to afford travel to the clinic or medical fees, limited or inaccurate information about the benefits of vaccines, or procrastinating or forgetting appointments in the face of limited time and competing priorities. Providing incentives, text message reminders, and information about the benefits of vaccines can make parents more likely to vaccinate their children.

Bundling approaches that increase demand for vaccines can maximize their impact. For example, combining small mobile phone credit incentives for families, “nudge” text message reminders to caregivers, and information about the benefits of vaccines through community “ambassadors” helped boost immunization in India by more than 40 percent. The bundled approach was most effective in lower-income areas with low initial vaccine levels, where it increased the immunization rate six-fold (approximately 500 percent).

Immunization is already a highly cost-effective way of improving child survival. Programs that increase families’ demand for vaccines can make it even more cost-effective. In India, researchers used machine learning to test 75 unique combinations of reminder SMS texts, mobile phone credit incentives, and local immunization ambassadors to spread information. The most cost-effective bundle combined text message reminders with community ambassadors and omitted incentives. This policy increased the number of immunizations per dollar by about 9 percent relative to those receiving standard services, and reduced the cost per immunization.

Providing incentives for parents alongside other interventions can improve cost-effectiveness. In an earlier example from India, giving families a small incentive—a package of lentils for each vaccine and a set of plates when kids finished the full immunization course—at an immunization camp not only increased immunization coverage, but also cut costs in half, from US$50 to US$25 per fully immunized child. Camps that gave incentives were also busier and used the nurses’ time more efficiently.

Programs to improve health workers’ job performance should be designed with local contexts in mind. In Uganda, for example, a community monitoring and information program improved vaccine coverage at a time when only 66 percent of children in Uganda were fully vaccinated, but a similar program implemented later had limited impact once full immunization coverage across the country had improved to 85 percent. This suggests monitoring programs may be more effective in areas where vaccine coverage is low. Similarly, incentivizing good job performance through pay-for-performance programs may be most impactful in health systems with high levels of transparency and accountability, and when accompanied by interventions to increase demand for health care services, like cash transfers and information campaigns.

Providing families with actionable information from socially influential community members is more effective than sharing general health information. Social networks can be useful tools to spread important information, like when and where vaccines are available and the presence of incentives, and can amplify the effects of other interventions. Spreading messages through local community "ambassadors" via phone or word-of-mouth can also increase demand by sharing the benefits of immunization or keeping vaccines salient for their communities. Still, information alone is sometimes not enough to shift behavior if families face other barriers like cost; in these cases, pairing information with incentives can help boost coverage.