Illustratrion representing a colony of Neisseria meningitidis bacteria

What is invasive meningococcal disease (IMD)?

IMD is an unpredictable infection that can quickly become life-threatening.1

What is IMD?

Icon representing Meningococci

IMD is a rare and unpredictable infection caused by the bacteria Neisseria meningitidis, also known as meningococci.1,2

Icon representing the urgency needed to treat the symptoms of meningitis

IMD can progress rapidly and become lethal within 24 hours.1

Icon schematically displaying the complications of meningitis

People who survive IMD can develop life-changing and long-term complications.3

Multiple serogroups of Neisseria Meningitidis can cause IMD

Icons representing different strains of Meningococci
Icons representing different strains of Meningococci

N. Meningitidis are gram-negative bacteria classified into different serogroups based on the structure of their outer surface.1 Six major serogroups of N. Meningitidis – A, B, C, W, Y and X – are responsible for most cases of IMD worldwide.4 Serogroups B, C, W and Y are responsible for most cases of IMD in England.1,5 There is also seasonal variation in the diagnosis of IMD, with most cases reported in the winter months.1

Many people are asymptomatic carriers of meningococci

Meningococci colonise the nasopharynx of humans. Around 10% of the UK population are asymptomatic carriers of meningococci.6 Carriage rates are higher in adolescents and young adults, and lower in infants and young children.1
In many people, colonisation and carrying meningococci is harmless and asymptomatic; however, they are still able to unknowingly transmit the infection to other people.1 It is not fully understood why IMD develops in some individuals and not others.1

Meningococci are transmitted primarily through respiratory secretions

Icon representing a person sneezing

Meningococci are transmitted through respiratory droplets or particles in the air, or direct contact with mucus, phlegm or saliva of an individual carrying meningococci.1

Icon representing a clock

Frequent or prolonged exposure to the bacteria is usually required for infection.1

IMD manifests as meningococcal meningitis, meningococcal sepsis or a combination of both

The symptoms of IMD vary depending on whether it manifests as meningococcal meningitis or meningococcal sepsis. Symptoms also typically differ between infants and adults.7 Some examples of symptoms are described below, but other signs and symptoms may occur.

Illustration representing colonisation by meningococci of the nasopharynx and bloodstream

Following colonisation of the nasopharynx, meningococci can invade the bloodstream in a small number of individuals8,9

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In meningococcal meningitis, meningococci cross the blood–brain barrier and attack the meninges.8

Illustration representing the symptoms of meningococcal meningitis in adults

In meningococcal sepsis, meningococci in the bloodstream cause an extreme immune response, endothelial damage, capillary leakage, tissue necrosis and organ dysfunction.8,10,11

Illustration representing the symptoms of meningococcal sepsis in adults

Certain groups are at an increased risk of developing IMD

Anyone can develop IMD, but certain characteristics and settings make some people more likely to develop the disease than others, including the following:

  • Age1,12

    Young children under the age of five years old, especially those under one year old, are at the highest risk of developing IMD. Those aged 11 to 24 years old and adults over 65 years old are also at an increased risk of developing IMD.

  • People who live in the same household as, or have close, prolonged contact with, patients with IMD or carriers of meningococci are at a higher risk of meningococcal infection due to the potential for exposure to respiratory droplets or secretions.

  • People with the following pre-existing medical conditions are at an increased risk of developing IMD:

    • HIV infection
    • Asplenia or splenic dysfunction
    • Persistent complement component deficiencies

  • People receiving certain types of medications, including complement inhibitors, are at an increased risk of developing IMD.

  • People can be at an increased risk of developing IMD if they live in close quarters with lots of other people or because of their occupation. Settings that increase the risk of developing IMD include:

    • University halls of residence
    • Military barracks
    • Working in a laboratory and handling strains of, or clinical samples containing meningococci
Image representing science through display of a culture cell plate

Epidemiology

Read more about the incidence of IMD and its impact on individuals and society

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Diagnosis

Read more about the symptoms of IMD to look out for and how these might differ between infants and adults

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References

  1. UK Health Security Agency. The Green Book: Meningococcal, Chapter 22 (June 2025). https://www.gov.uk/government/publications/meningococcal-the-green-book-chapter-22 (accessed December 2025).
  2. National Institute for Health and Care Excellence. Meningitis - bacterial meningitis and meningococcal disease: How common is it? https://cks.nice.org.uk/topics/meningitis-bacterial-meningitis-meningococcal-disease/background-information/prevalence/ (accessed December 2025).
  3. Olbrich KJ et al. Systematic review of invasive meningococcal disease: sequelae and quality of life impact on patients and their caregivers. Infect Dis Ther 2018;7:421-438.
  4. UK Health Security Agency. Guidance for public health management of meningococcal disease in the UK. https://www.gov.uk/government/publications/meningococcal-disease-guidance-on-public-health-management. (accessed December 2025).
  5. UK Health Security Agency. Invasive meningococcal disease in England: annual laboratory-confirmed reports for epidemiological year 2024 to 2025. https://www.gov.uk/government/publications/meningococcal-disease-laboratory-confirmed-cases-in-england-2024-to-2025/invasive-meningococcal-disease-in-england-annual-laboratory-confirmed-reports-for-epidemiological-year-2024-to-2025 (accessed December 2025).
  6. UK Health Security Agency. Meningococcal disease: guidance, data and analysis. https://www.gov.uk/government/collections/meningococcal-disease-guidance-data-and-analysis (accessed December 2025).
  7. National Institute for Health and Care Excellence. Clinical Knowledge Summaries. Meningitis - bacterial meningitis and meningococcal disease: When should I suspect bacterial meningitis or meningococcal disease? https://cks.nice.org.uk/topics/meningitis-bacterial-meningitis-meningococcal-disease/diagnosis/when-to-suspect/ (accessed December 2025).
  8. Coureuil M et al. Pathogenesis of meningococcemia. Cold Spring Harb Perspect Med 2013;3:a012393.
  9. Rosenstein NE et al. Meningococcal disease. N Engl J Med 2001;344:1378-1388.
  10. McGill F et al. The UK joint specialist societies guideline on the diagnosis and management of acute meningitis and meningococcal sepsis in immunocompetent adults. J Infect 2016;72:405-438.
  11. Rausch-Phung E et al. Meningococcal Disease (Neisseria meningitidis Infection), in StatPearls [Internet]. 2025, Treasure Island (FL): StatPearls Publishing.
  12. British Medical Journal. BMJ Best Practice. Meningococcal disease - Symptoms, diagnosis and treatment. 2025. https://bestpractice.bmj.com/topics/en-gb/542 (accessed December 2025).
  13. National Institute for Health and Care Excellence. Clinical knowledge summaries. Meningitis - bacterial meningitis and meningococcal disease: What are the risk factors for bacterial meningitis and meningococcal disease? https://cks.nice.org.uk/topics/meningitis-bacterial-meningitis-meningococcal-disease/background-information/risk-factors/ (accessed December 2025).

Adverse events should be reported. Reporting forms and information can be found at https://yellowcard.mhra.gov.uk/. Adverse events should also be reported to GlaxoSmithKline on 0800 221 441.

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January 2026 | NP-GB-MNU-WCNT-250005 (V1.0)