First year of ongoing invasive Haemophilus influenzae type b outbreak among middle-aged people who use drugs and people who experience homelessness in Hamburg, Germany, September 2024 to August 2025

We report an ongoing outbreak of invasive Haemophilus influenzae type b (Hib) disease among people who use drugs (PWUD) and people experiencing homelessness (PEH) in Hamburg, Germany. Between 1 September 2024 and 31 August 2025, 20 adult Hib cases were reported. The cases were either residents of Hamburg (16/20) or stayed in Hamburg during the exposure period (4/20). Whole genome sequencing identified a link between 18 cases (median age 50 years (range 26–77); six female, 12 male, three died). An epidemiological link (i.e. drug consumption in the open drug scene) could be established for 15 of the 18 cases. Control measures included post-exposure chemoprophylaxis for close contacts (n = 4), vaccination offers (n = 69 doses administered by 31 August 2025) and an information campaign targeting PWUD, PEH and staff members of addiction support centres. We describe the first Hib outbreak among adults in Europe and document drug use and homelessness as suspected risk factors. Based on these findings, national vaccination recommendations issued by the Standing Committee on Vaccination in Germany (STIKO) were updated to include vaccination and post-exposure prophylaxis recommendations in outbreak settings for PWUD and PEH. Control measures are currently being evaluated and expanded.