The document summarizes the objectives and activities of the EU-Joint Action on Vaccination (EU-JAV) work package 5 (WP5), which aims to strengthen interaction between immunization information systems (IIS) in Europe. WP5 will assess IIS interoperability, test estimating measles-mumps-rubella vaccine coverage across Europe using IIS data, and evaluate vaccine reminder systems. The goals are to increase vaccine surveillance capabilities, coverage, and support research using combined European vaccine data. WP5 involves 20 EU countries and is led by Denmark and Croatia over 3 years with a €5.8 million budget.