Vaccination is one of public health’s most successful tools for preventing and controlling the spread of infectious diseases and, increasingly, cancers and chronic diseases too. Immunization is an effective and cost-efficient strategy that prevents sickness and death in all age groups and saves billions of dollars each year. The COVID-19 epidemic and recent outbreaks of measles and other preventable infectious diseases underscore the importance of vaccines and sustaining high vaccination rates. Work is needed to ensure that people of all ages receive a complete series of the vaccines they need.