Many communities around the world continue to face barriers to accessing routine childhood immunization services, resulting in an estimated 18 million children worldwide who do not receive any lifesaving vaccines (zero-dose children) and an additional 25 million who do not complete the recommended vaccination schedule. Challenges and barriers may include access to quality and reliable services, financial burdens, or a reluctance to seek vaccination because of distrust, negative experiences, or concerns over safety and side effects .

The majority of unvaccinated and undervaccinated children live in low- and middle-income countries, highlighting the pressing need to prioritize sustainable improvements in immunization programs and approaches to increase community acceptance and access to lifesaving vaccines in the poorest and most vulnerable countries in the world . In addition to safe and effective vaccines and an efficient supply chain, a successful immunization program also requires communities and individuals who are willing and able to receive vaccines for themselves and their children . The COVID-19 pandemic focused attention on the importance of vaccine confidence and demand for immunization, whereby many countries witnessed a growing distrust toward recommended prevention measures and the government, health systems, and institutions delivering new vaccines.

Immunization demand refers to individuals and communities with a positive attitude toward vaccines, positive perceptions about the quality of services available to them, and actively seek out and advocate for others to use these services. Rumors and distrust may flare up at any time, not only during a pandemic or novel health emergency. This reflects the complex process involved in vaccine decision-making, influenced by personal experience, perceptions of the institutions involved, and confidence in those institutions . The local community, health system, media environment, social norms, and individual perceptions operate in an iterative cycle to influence vaccine uptake and demand for immunization. 

However, the success of any program will depend on careful planning, formative research, and meaningful user engagement.