Key Points

• A notable shift in the epidemiology of invasive meningococcal disease (IMD) in 2022 following two years of low incidence, notably:

  • An early and high peak in the number of IIM cases in December 2022;

  • A marked increase in IIM Y and W compared to the pre-COVID-19 pandemic period;

  • Heterogeneity in the age of cases by serogroup, notably with a significant proportion of B and W IIM cases among infants, B and Y IIM cases among 15- to 24-year-olds, and Y and W IIM cases among those aged 60 and older;

  • The emergence of strains causing epidemics and hyperendemic outbreaks of IIM B among young adults in certain regions;

  • Altered clonal diversity, notably with the expansion of ST-9316 W strains previously described in the Hauts-de-France region between 2015 and 2018;

  • A higher case-fatality rate for IIM W compared to other serogroups, partly linked to the expansion of ST-9316 strains;

  • The very low incidence of IIM C, likely due to the establishment of herd immunity linked to the gradual increase in vaccination coverage among adolescents, which must be maintained over time.

• The marked resurgence of IIMs could be explained by the resumption of meningococcal transmission in a population with reduced immunity, given lower exposure to meningococci during the COVID-19 period, against a backdrop of concurrent epidemics of respiratory viral infections at the end of 2022.

• The meningococcal vaccination strategy will soon be reevaluated by the French National Authority for Health (HAS) based on recent trends in the epidemiology of IIM.