Prevention

The only means of preventing bacterial meningitis is by vaccination.

How vaccines work

Vaccines are given to prepare the immune system before exposure to a germ so that it is better able to fight an infection when it occurs. Vaccines contain either parts of a germ, live but weakened germs, or inactivated (dead) germs. Germs contain very specific proteins and sugars (called polysaccharides) on their surfaces that are called antigens. The antigens stimulate the immune system to produce protective proteins (antibodies) and immune cells (lymphocytes). When the vaccine is given, the immune system reacts as if the germ has entered the body. It produces specific antibodies and lymphocytes responsible for immunity against the germ. When a vaccinated person is subsequently exposed to the germ, the immune system is able to recognize the germ right away and eliminate it before it can cause harm. Some vaccines may need to be given more than once in order to establish adequate immunity.

Before a vaccine can be approved for use, it must be thoroughly tested for safety and effectiveness. All of the vaccines available to prevent meningitis have now been used for a number of years and millions of doses have been administered. Vaccines are constantly monitored to ensure that there are no serious adverse events. Minor reactions that commonly occur after any vaccination include redness, swelling, and pain at the injection site, fever, loss of appetite, aches and pains. These common reactions subside with 1-2 days.

How vaccines are made

All of the meningitis vaccines share similarities in production and composition. The meningitis bacteria are grown, then killed, and the complex molecules called polysaccharides, which forms the external coat of the bacteria, are extracted and purified. Two forms of vaccine can then be produced: one composed of the pure polysaccharide (called polysaccharide-only vaccines) and the other in which the polysaccharide is chemically linked or conjugated to a protein (called conjugated vaccines). The proteins used in the conjugated vaccines are themselves derived from different bacteria or bacterial products. The high level of chemical purity of these vaccines means that they have proven to be extremely safe. Because they are composed of highly purified material there is no possibility of contracting meningitis or any other disease from these vaccines.

The polysaccharide-only vaccines have proven to be very effective in adults and adolescents, but are not effective in infants. Fortunately, the conjugated vaccines are very effective at all ages, including infants. A series of 2-3 injections starting at 2 months of age followed by a booster 9 to 12 months later form the usual schedule for the immunization of infants.

The following vaccines have been developed to prevent the three major causes of bacterial meningitis:

Meningococcal vaccines:

Polysaccharide-only vaccines: These are for use in older children, adolescents and adults for control of outbreaks or in situations of increased risk (military recruits, university students, travelers). They are:

• Combined groups A and C vaccine
• Combined groups A-C-Y-W135 vaccine

Conjugated vaccines: These are for use in the routine immunization of infants, children, and adolescents. They are:

•  Conjugate group C vaccine
• Conjugate groups A-C-Y-W135 vaccine

A conjugate group A vaccine for use in Africa is being developed by the Meningitis Vaccine Project. This vaccine has the ability to reduce and control epidemic meningococcal meningitis in the Sub-Saharan meningitis belt.

Vaccines against group B meningococci are not yet available. Some vaccines have been developed against specific strains of serogroup B and used in Cuba, Norway, and New Zealand. However these vaccines do not protect against all strains of serogroup B meningococci and are therefore not suitable for routine use. A new vaccine against serogroup B meningococci containing proteins common to strains of serogroup B is currently under development. When it becomes available it will mean that vaccines will be available for all of the major causes of bacterial meningitis.

Pneumococcal vaccines:

Polysaccharide-only vaccine: These are for routine use in those over 65 years of age and in those over 5 years of age with underlying medical conditions making them at increased risk of invasive pneumococcal disease (e.g. sickle cell disease, dysfunction or absence of spleen, chronic heart disease, chronic lung disease, cirrhosis, alcoholism, HIV infection).  A Combined polysaccharide vaccine against the 23 most common serotypes causing invasive pneumococcal disease in those 5 years of age and older is available.

Conjugated vaccines:  The first approved conjugated pneumococcal vaccine against the 7 most common serotypes causing disease in children under 5 years of age has been widely used in USA, Canada, and more recently in UK, Australia, and elsewhere. Newer conjugated vaccines with 10 and 13 serotypes are now available and as well as being used in industrialized countries, are also being evaluated for use in developing countries where different serotypes are required.

Haemophilus influenzae type b (Hib vaccine):

Polysaccharide-only vaccine: The first Hib vaccine was a polysaccharide only vaccine. Although it provided protection in children 2-5 years of age, it was not effective in infants less than 18 months of age.

Conjugated vaccines: have proven to be highly effective in preventing invasive Hib disease and are recommended for routine use in all infants.

Vaccines are the only way to prevent bacterial meningitis. However, their availability differs in different parts of the world. There is a long way to go to protect the world’s children. The World Health Organization (WHO) estimates that, since 2005, 21% of eligible children have been vaccinated against Hib. The WHO does not provide any estimates yet of the proportion of children who have received pneumococcal and meningococcal vaccine, however an interactive tool is available on the WHO website which enables the user to determine which countries have meningitis vaccines in their childhood schedules.