Key Points

In 2023, the incidence of invasive meningococcal disease (IMD) returned to pre-COVID-19 pandemic levels, with varying trends depending on serogroup and age. Notable trends were observed in 2023:

• 560 cases of IIM reported in 2023, representing a reported incidence rate of 0.82 per 100,000 population

• An early and very high peak in IIM incidence during the winter of 2022/23; then, in the second half of the year, a return to levels observed during pre-pandemic seasons

• Distribution by serogroup: 240 cases of IIM B (44% of cases with known serogroup), 160 cases of IIM W (29%), 130 cases of IIM Y (24%), and a very small proportion of serogroup C (<1% of cases)

• A sharp increase in the number of W IIM cases (2.5 times higher than in 2022) and Y IIM cases (1.7 times higher than in 2022) to levels never previously observed

• Higher risk of W IIM among infants and adults in various age groups

• Higher risk of IIM Y among the elderly and, to a lesser extent, among 15- to 24-year-olds

• High case fatality rate for IIM W (19%) compared to other serogroups (7% for IIM B and 8% for IIM Y), confirming the virulence of serogroup W/cc11 strains and suggesting increased virulence of W/cc9316 strains compared to the pre-pandemic period

• Return of IIM B to levels equivalent to those observed before the pandemic (all ages combined) but with contrasting trends depending on age

• Decrease in the incidence of IIM B among infants compared to the pre-pandemic period, but levels remain high, prompting efforts to increase vaccination coverage among infants for the meningococcal B vaccine

• Very low levels of IIM C, which fell following measures to strengthen vaccination among infants (2017: dose at 5 months, 2018: mandatory vaccination) and a trend that continued thereafter thanks to measures implemented during the pandemic

Epidemiological data on IIM in 2022 and 2023 contributed to the work of the French National Authority for Health (HAS) on revising the meningococcal vaccination strategy.