Summary: Complex humanitarian situations, such as the large and sudden influx of Ukrainian war refugees and migrants to Poland and other European countries after the outbreak of the war on February 24, 2022, may present both individual and public health challenges, including for immunization. Immunization is one of the world’s most successful and cost-effective public health interventions. It is of key importance to provide migrants and war refugees with the same level of protection in terms of the prevention and control of infectious diseases, including vaccine-preventable diseases, as the population of the country they arrive in. Low vaccination rates result in both health and social consequences for the entire population and an overload of health care systems. Strategies to increase vaccine acceptance and uptake include tailoring vaccination services to increase coverage of unreached and/or specific populations, developing effective health communication campaigns, collecting vaccination status data, and promoting cooperation between public health authorities at the national and international levels. Ensuring the continuity of childhood routine immunization and closing gaps in vaccination coverage are important elements in supporting the delivery of health care for those vulnerable populations. Health systems should incorporate the needs of refugees and migrants in national and local health policies.