From multiple measles genotype D8 introductions in 2024 to sustained B3 local transmission in and around Milan, northern Italy, January to April 2025

Abstract

In 2024, the Metropolitan City of Milan and surrounding areas in northern Italy (ca 4 million people) experienced a measles epidemic caused by multiple introductions of different genotype D8 lineages, which led to small outbreaks, mostly linked to importation events and/or vulnerable population groups, without evidence of sustained local circulation [1]. As Subnational Reference Laboratory of the Italian measles and rubella surveillance network (MoRoNet), we now report a new surge of measles in the same area in 2025, driven by a unique lineage of genotype B3, causing locally acquired cases