by Dr. Milton Lum
The bacterium Neisseria meningitides causes meningitis, which is an infection of the membrane surrounding the brain and spinal cord, and septicaemia, which is an infection of the blood. There are at least 12 groups of the bacterium, which are characterised by differences in its capsule. Groups A, B and C cause the majority of meningococcal meningitis. The Y and W135 groups are increasingly important as they have been the cause of recent outbreaks and epidemics.
The meningococcus is spread by aerosol or direct contact with secretions from the nose or throat of infected persons or healthy carriers. About 5% to 15% of adolescents and young adults are carriers of the bacterium. The carrier rates in children are much lower (about 1%).
The clinical features of meningococcal meningitis are acute onset of fever, headache, nausea, vomiting, and stiff neck. There may be lethargy, delirium, coma and fits. A rash may appear on the skin. Infants with the infection may appear lethargic, irritable and go off their feeds.
About 50% of untreated cases in children result in death. The mortality rate with treatment is between 5% and 10%. Significant neurological disabilities like mental disorders, deafness, paralysis and fits occur in about 10% to 15% of those who survive. When there is also infection of the blood stream (septicaemia), the mortality rate may be more than 15% to 20%.
The risk of meningococcal infection is increased in those who are immune-deficient from various conditions such as HIV and those who do not have a spleen for various reasons.
As a consequence of the control of haemophilus influenza type B infections with immunisation, Neisseria meningitides has become the leading cause of bacterial meningitis in children and adults in many countries. The meningococcus is the only bacterium that causes epidemics of meningitis. There is rapid spread of the infection in an epidemic, leading to deaths occurring in a day or two and/or serious neurological disabilities, even if the treatment is apparently adequate. The incidence of meningococcal infection in Malaysia is unknown as it is not a notifiable disease.
There are different types of meningococcal vaccine. One vaccine protects against group C (or group C conjugate vaccine). Another vaccine protects against groups A and C (or the bivalent meningococcal vaccine). The vaccine called the ACWY vaccine (or the quadrivalent meningococcal vaccine) protects against groups A, C, Y and W135.
Another quadrivalent meningococcal vaccine is combined with the diphtheria vaccine. There is currently no vaccine that protects against Group B meningococcal infection. The vaccines provide protection by stimulating the body to produce antibodies against the meningococcus.
The meningococcal vaccines currently available are very safe and effective in children above 2 years old and adults. The vaccine against group A meningococcus stimulates a poorer antibody response and has a shorter duration of protection in children below the age of 2 years.
The vaccine against group C meningococcus does not stimulate an antibody response in the same age group. As such, groups A and C vaccine are not used in routine infant immunisation. However, when there are outbreaks of meningococcal meningitis, groups A and C vaccine may be given to children below two years of age.
It is known that non-conjugated group C vaccines, when given to infants, may lead to decreased antibody response to the bacterium in later years. The significance of this is unknown.
The group C conjugate vaccine is, however, effective, in all age groups including infants. This vaccine is used in the national immunisation programmes in many countries to immunise those whose risks of infection are high and during outbreaks or epidemics.
The quadrivalent vaccine (groups A, C, W135 and Y) does not protect against group B infections, which is a cause of some outbreaks or epidemics. This vaccine is also not very effective in children below 18 months of age. There is a belief that widespread use of the quadrivalent vaccine may reduce or do away with the need for mass vaccination in outbreaks or epidemics.
Meningococcal vaccines are well tolerated and systemic reactions are very uncommon. The most common adverse reactions are redness and transient fever. Serious adverse events like hypersensitivity reactions (including anaphylaxis), bronchospasm and angioedema) are rare. Fits and purpura had been linked to the group C conjugate vaccine but no causal relationship has been found.
There is no evidence that the vaccine is unsafe in pregnancy but it is usually avoided unless the mother is at increased risk of meningococcal infections. Vaccination is not advised in those who have had a previous hypersensitivity reaction to any component of the vaccine including tetanus toxoid or diphtheria vaccine.
The vaccine against group C is offered to all babies as part of childhood immunisation in many developed countries. It is, however, optional in Malaysia. It is believed that a single dose provides lifelong immunity.
Immunisation with the quadrivalent (ACWY) vaccine is recommended when one travels to areas where the risk of infection is increased, for instance, areas of sub-Saharan Africa and Saudi Arabia. The doctor will advise on the need for this vaccine.
Pilgrims to Saudi Arabia are at increased risk of getting meningococcal infection as there have been outbreaks in recently. Proof of immunisation with the quadrivalent (ACWY) vaccine is a requirement for those performing the haj or umrah.
If one has been vaccinated with the groups A and C vaccine previously, one should be vaccinated again with the quadrivalent (ACWY) vaccine. Close household or institutional contacts of persons with meningococcal infection may be offered immunisation.
The meningococcal vaccines are safe and do not interfere with other vaccines given simultaneously. Its introduction has reduced the incidence of meningococcal infection considerably. It offers the hope of reduction or elimination of meningococcal infection and its consequences, including death and neurological disabilities.
More info on MENINGITIS here.
by Dr. Milton Lum