Meningococcal disease refers to any illness caused by the bacterium Neisseria meningitidis.¹ There are six common serogroups of bacteria that cause most meningococcal disease worldwide - A, B, C, W, X and Y.² The primary mode of transmission of Neisseria meningitidis is through respiratory droplet spread or by direct contact with respiratory secretions.²

Based on structural differences of the polysaccharide capsule, bacteria are classified into serogroups.¹ Neisseria meningitidis uses the polysaccharide capsule to evade destruction by the immune system, using a protective shell to prevent binding of the complement system that could otherwise initiate lysis and phagocytosis. The complement-bacterium complex is called the C3b.³ Evasion can be enhanced by other methods including mimicry of host molecules, recruiting factor H and its genetic diversity.³

Figure 1: Polysaccharide capsule mechanism. Adapted from Tan LKK, Carlone GM, Borrow R. Advances in the development of vaccines against Neisseria meningitidis. N Engl J Med. 2010; 362:1511-20.

Meningococcal disease has an incubation period of typically 3 to 4 days, with a range of 1 to 10 days² 

Invasive meningococcal disease (IMD) is a major cause of meningitis and septicaemia.¹ Common symptoms of meningococcal meningitis include fever, headache, neck stiffness, altered mental status, nausea, vomiting and photophobia.¹ Meningococcal sepsis symptoms typically include fever, a petechial or purpuric rash, septic shock, disseminated intravascular coagulation and multiple organ failure.¹

In 1906, scientists began to recommend anti-meningococcal serum therapy to protect humans against meningococcal disease; a therapy based on antibodies initially derived from the blood of horses, and later from patients, or individuals recovering from meningococcal disease.⁴ Antibiotics revolutionised treatment for meningitis; however, they do not always act fast enough to prevent damage that the bacteria can cause. Ireland introduced a vaccine against meningococcal C disease (MenC vaccine) in 2000, meningococcal B disease (MenB vaccine) in 2016 and meningococcal ACWY disease (MenACWY vaccine) in 2019.^5,6