Untreated, bacterial meningitis is almost always fatal. Viral meningitis, in contrast, tends to resolve spontaneously and is rarely fatal. With treatment, mortality (risk of death) from bacterial meningitis depends on the age of the patient and the underlying cause. Of the newborn patients, 20–30% may die from an episode of bacterial meningitis. This risk is much lower in older children, whose mortality is about 2%, but rises again to about 19–37% in adults. In adults, 66% of all cases emerge without disability. The main problems are deafness (in 14%) and cognitive impairment (in 10%).
Meningococcal disease occurs in epidemics in areas where many people live together for the first time, such as army barracks during mobilization, college campuses
There are significant differences in the local distribution of causes for bacterial meningitis. For instance, ''N. meningitides'' groups B and C cause most disease episodes in Europe, while group A meningococci are more common in China and amongst Hajj pilgrims. In the "meningitis belt" of Africa, group A and C meningococci cause most of the outbreaks. Group W135 meningococci have caused several recent epidemics in Africa and during the Hajj. These differences are expected to change further as vaccines against common strains are introduced. Similarly, immunization against mumps has led to a sharp fall in the number of cases of mumps meningitis, which prior to vaccination occurred in 15% of all cases of mumps. In countries where the vaccine for meningococcus group C was introduced, cases caused by this pathogen have decreased substantially. The pneumococcal polysaccharide vaccine, which covers 23 strains, is only administered in certain groups (e.g. those who have had a splenectomy, the surgical removal of the spleen); it does not elicit a significant immune response in all recipients, e.g. small children.
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