Meningococcal disease is caused by various serogroups of Neisseria meningitidis (N. meningitidis), of which groups A, B, C, W, Y account for about 95% of meningococcal disease. N. meningitidis is one of the most common causes of bacterial meningitis in the world and the only bacterium capable of generating large epidemics of meningitis.

Meningococcus is transmitted by aerosol or direct contact with respiratory secretions of patients or healthy human carriers.

Meningitis and sepsis are the major clinical features of infection with N. meningitidis. Meningitis frequently presents with fever, headache and neck stiffness, and is often accompanied by other symptoms, such as altered mental status, nausea, vomiting and photophobia. Meningococcal sepsis is characterised by fever and a purpuric rash, often accompanied by septic shock, disseminated intravascular coagulation and multiple organ failure. Often a rapid progression of the disease, with an 8-15% case-fatality ratio. This may result in death within one or two days after onset of symptoms.