There are three main clinical forms of the disease: the meningeal syndrome, the septic form and pneumonia.
The onset of symptoms is sudden and death can follow within hours. In as many as 10-15% of survivors, there are severe persistent neurological defects, including hearing loss, speech disorders, loss of limbs, mental retardation or paralysis.
Survivors can suffer persistent neurological defects. Up to 5-10% of a population may be asymptomatic carriers. The WHO says waning immunity among the population can lead to epidemics, as can overcrowding (such as in student dormitories) and certain climatic conditions.
Effective vaccines are available against most major serotypes (A,C,W,Y) of the bacteria. A vaccine against type B is under development.
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This article is part of a series compiled by Vaccines Today to raise awareness of European Immunization Week 2011 which runs from 23-30 April