On March 3, 2005, the Lorraine Regional Health Directorate (DRASS) alerted the Eastern Regional Health Agency (CIRE) to 11 deaths at a nursing home. Four residents tested positive for pneumococci in their sputum. The Regional Health Committee (CRH) had taken initial measures and conducted a review of hygiene practices. On March 4, the Departmental Health and Social Affairs Service (DDASS) and the Cire launched the investigation. The attack rates among residents and staff reached 50% and 35%, respectively, while influenza vaccination coverage stood at 93% and 31%. Only one resident had been vaccinated against pneumococcus. The epidemic peaked on February 19, with high staff involvement at the outset (peaking on the 15th). The case-fatality rate was 21% among residents. Symptoms among staff were dominated by flu-like syndrome, whereas residents presented with lower respiratory tract infections (LRTI) accompanied by moderate fever and productive cough. The analyzed pneumococcal strains were all different, and the influenza virus, tested for at the end of the outbreak, remained the only common source identified. Among staff, attack rates doubled depending on vaccination status, whereas they did not vary among residents. However, the vaccine’s effectiveness in preventing deaths was demonstrated. Two hypotheses are discussed: - the presence of the influenza virus at the start of the outbreak with bacterial superinfection in residents; - the succession of two distinct infectious episodes, the second caused by the influenza virus. Following the late alert, the control measures recommended in the September 2004 “influenza circular” were implemented rapidly, though with significant difficulties in implementation (budget, staff availability). Furthermore, there is no evidence here to demonstrate the efficacy of Oseltamivir (Tamiflu®). (R.A.)