English summary: Invasive meningococcal diseases in conscripts in 2003-2012

Introduction

In Finland, people completing their military service are vaccinated against invasive meningococcal diseases using a quadrivalent vaccine. The vaccine given provides immunization against meningococcal serotypes A, C, W and Y. The literature suggests that invasive meningococcal disease occurs more often among soldiers than in the general population. So far, no practicable B serotype vaccine has been available. Since a B serotype vaccine has now come on the market, in this study we wished to determine the incidence of meningococcal disease among conscripts.

Methods

The study is register based and a retrospective cohort study. The incidence of invasive meningococcal disease (meningococcal meningitis) and sepsis among people completing their military service was studied in terms of morbidity for the period 2002−2012 and in terms of mortality for the period 1993−2012. The diagnoses were obtained from the Defence Forces electronic patient information system, which was only available to all garrison health centres from the early 2000s. The results were reviewed using case histories and the infectious disease register maintained by the National Institute for Health and Welfare. Mortality was verified by working through the death certificates of conscripts for the period researched. The results were expressed in relation to person-years of military service, and compared to statistics from the national infectious disease registry.

Results

During the period 2003−2012, a total of 33 cases of meningococcal or other bacterial meningitis or sepsis were discovered. Twenty eight of the outbreaks were caused by meningococcus serotype B. In 1993−2012 a total of five conscripts died of meningococcal sepsis. The incidence of invasive meningococcal disease among conscripts was 17 cases, of which B serotype accounted for 16 cases, and the mortality 1.4 cases per 100,000 person-years. The respective incidence of meningococcal disease at the national level in the age group 15-29 years was 1.3 cases, of which B serotype accounted for 0.9 per 100,000 person-years.

Conclusions

Among basically healthy conscripts the incidence of invasive meningococcal disease is a cause for concern since the incidence of the disease is higher than in the general population and the disease in conscripts is also associated with mortality. In almost all cases the meningococcus was confirmed as B serotype, against which the current quadrivalent vaccine does not provide protection. Expansion of vaccination protection seems the only way to reduce morbidity. Significant additional evidence is expected soon in Europe on the clinical efficacy of newly available B serotype meningococcal vaccines. If experience gained over the next few years on the protective efficacy of B group vaccines proves encouraging, it will be appropriate to commence immunization among Finnish conscripts.