Bacterial meningitis is an infection of the fluid surrounding the brain and spinal cord. Three species of bacteria account for more than 80 percent of all cases of meningitis: Neisseria meningitides, Hemophilus influenzae, and Streptococcus pnewmoiae. All three are normally present in the external environment and may even reside in a person’s nose and respiratory system without causing harm. Occasionally these organisms infect the brain without an identifiable reason. In other cases, infection follows a head injury or results from an abnormality in the immune system. Small epidemics of meningococcal meningitis may occur in environments such as military training caps, college dormitories, or among other groups of people in close contact.
A vaccine can help prevent meningitis. There are two kinds of meningococcal vaccine in the U.S.:
- Meningococcal conjugate vaccine (MCV4). It is the preferred vaccine for people age two through 55 years.
- Meningococcal polysaccharide vaccine (MPSV4), which may be used if MCV4 is not available, and is the only meningococcal vaccine licensed for people older than 55.
Both vaccines can prevent four types of meningococcal disease, including two of the three types most common in the United States and a type that causes epidemics in Africa. Meningococcal vaccines cannot prevent all types of the disease, however, they do protect many people who might become sick without the vaccine.