Key Points

• A significant resurgence of invasive meningococcal disease (IMD) was observed during the 2024–2025 season, with an exceptionally high number of cases in January 2025 (90 cases, unconsolidated data). For the entire year of 2024, 615 cases of IIM were reported in France, representing the highest annual number of cases since 2010.

• The number of cases reported and occurring in January 2025 is equivalent to that observed at the peak reached in December 2022 amid a post-pandemic resurgence of COVID-19 and a significant influenza epidemic associated with the widespread circulation of other respiratory viruses (SARS-CoV-2 and RSV).

• The increase in IIM in January 2025 may be linked in part to the particularly severe influenza epidemic during the 2024–2025 season. Indeed, it has been shown that influenza virus infections can increase the risk of invasive meningococcal infection.

• A comparison of the characteristics of IIM cases occurring during December–January in the 2022–2023 and 2024–2025 seasons reveals similar patterns in terms of age and serogroup. IMIs linked to serogroup B remain the most common, followed by serogroup W and serogroup Y IMIs. Serogroup W and Y IMIs have increased significantly in recent years compared to the incidence recorded before the COVID-19 pandemic.

• The most recent data highlight the severity of IIM and its transmission potential:

  • The risk of IIM is high among infants in the first months of life, but numerous cases are also observed among adolescents and adults.

  • Fifty deaths were reported between July 2024 and January 2025, representing an overall case fatality rate of 13.7%. The case fatality rate for IIM W remains particularly high: it was 19.8%, compared to 12.5% for IIM B and 10.4% for IIM Y.

  • In January 2025, 13 deaths occurred, primarily among adults, including young adults, which underscores the severity of these infections.

  • Two clusters of IIM B cases were identified in January: three cases of IIM B among students in Lyon, and three cases of IIM B within the same family in Ille-et-Vilaine. These clusters led to measures aimed at preventing the risk of IIM in the affected populations.

• The rapid reporting of cases to Regional Health Agencies and the submission of biological samples to the National Reference Center for Meningococci and Haemophilus influenzae are essential for maintaining reactive surveillance and the early identification of any spatio-temporal clustering of cases.