THE INCIDENCE AND EARLY MORTALITY OF INVASIVE MENINGOCOCCAL DISEASE (IMD) IN FINLAND

H. Rinta-Kokko1, H. Nieminen1, K. Niinimäki1, F. Coste2, E. Langevin2, A. Soininen3 and A.A. Palmu1

1 FVR – Finnish Vaccine Research, RWE unit, Tampere, Finland, 2 Sanofi, Lyon, France, 3 Sanofi, Espoo, Finland

Introduction: The disease burden and long-term trends of IMD in Finland in 1995─2022 were assessed in this population-based observational register study. The first results are reported here.

Methods: A confirmed case of IMD was defined as detection of Neisseria meningitidis from blood or cerebrospinal fluid (CSF) reported to the population-based laboratory surveillance system. Case-fatality proportion (CFP) was calculated as the proportion of cases resulting in death within 30 days. The study was funded by Sanofi.

Results: Culture-confirmed IMD cases accounted for 98% (95% confidence interval: 96─98%) of the total 948 IMD cases, of which 31% (28─34%) were identified from CSF, 48% (45─51%) from blood and the rest 21% (19─24%) from CSF and blood. The proportion of clinical manifestation of meningitis differed by age from 60% (53─67%) and 65% (59─70%) in age-groups 0─4 and 15─24 years, respectively, to 17% (12─26%) in age-group ≥65 years.

The overall incidence per 100,000 person-years decreased from 1.14 (1.02─1.28) in 1995─1999 to 0.32 (0.26─0.40) in 2015─2019 and fell to 0.08 (0.05─0.14) during the COVID-19 pandemic. Incidence was highest among infants. Majority of all cases were caused by serogroup B (63%; 60─66%); serogroups C, Y and W accounted for 16% (13─18%), 13% (11─15%) and 3% (2─4%), respectively.

The overall CFP was 12% (10─14%): 15% (12─19%) among sepsis cases and 6% (3─9%) among meningitis cases. CFPs were highest for serogroups W (21%;9─41%) and C (19%; 14─27%). There were no significant trends in CFP by age-group over time.

Conclusions: Incidence of IMD due to all serogroups has decreased since 1995. CFP has remained stable.