War and other forms of conflict are frequently the culprit for disrupted immunization practices, as government attention and funding are diverted elsewhere and people are displaced due to fighting. In other instances, the causes are related to deficiencies in resources and infrastructure, such as limited quantities of vaccinations and/or insufficient cold storage in which to transport and maintain them. Challenges may also arise in the form of physical obstacles, with mountains or difficult terrain preventing delivery of immunizations to remote populations. Although these access concerns cumulatively remain the biggest barrier to achieving worldwide protection, the growing, widespread, anti-vaccination movement is sparking outbreaks of disease across the globe, reversing decades of progress in decreasing the prevalence of vaccine-preventable diseases. Once in the US, new immigrants have incentives to continue to receive recommended doses in each vaccine series. For refugees and others seeking to obtain lawful permanent residency (ie, a "green card"), they must complete the full complement of immunizations recommended by the US Centers for Disease Control and Prevention. In addition, in order to register for and keep their children enrolled in school, newly arrived families must comply with school vaccine requirements. Apart from these external drivers, immigrants are often internally motivated as well; they have seen vaccine-preventable illnesses in their home countries -- or heard about them from their parents or grandparents -- and desire to protect their families from these diseases.