Troubled Times, Changing Tides: A Seroprevalence Study on Meningococcal Immunity in France Between 2016 and 2024

Our results show a significant decline in anti-serogroup B IgG antibody levels after the lifting of NPIs (<i>p</i> < 0.0001) in line with reduced circulation. Anti-serogroup C IgG antibody levels increased incrementally (<i>p</i> = 0.0003), particularly in those aged 1-4 years, likely reflecting a catch-up in anti-meningococcal C vaccination coverage. Anti-serogroup W IgG antibody levels remained stable, suggesting sustained circulation, but shifted to young children in the post-NPI period, potentially due to a genotypic shift. Anti-serogroup Y IgG antibody levels transiently increased significantly (<i>p</i> < 0.0001) during the NPI period but then decreased back after their lifting. Anti-serogroup X IgG antibody levels remained stable, consistent with its low prevalence and the absence of targeted vaccination.