Meningococcal vaccines. Current status and future possibilities.

Meningococcal disease causes great emotion and anxiety in the families and caregivers of patients. Numbers of such patients are usually small in industrialised countries, unlike those in many regions--especially in subsahelian Africa. Vaccines have been tried for more than 80 years; at present there are available polysaccharide vaccines against groups A, C, Y and W135, and a protein-based vaccine against group B. A property common to all is their relative efficacy (75 to 100%) at school age and after, and an acceptably short persistence of antibodies. Small children pose the major challenge, in whom there is essentially evidence of clinical protection only against group A and C diseases. With vaccines against other serogroups protection is possible, but not yet proven in controlled clinical studies. The search is on for help from various modifications, including the conjugation technique, to transform the independent nature of polysaccharide response towards T cell dependence, as was done earlier in Haemophilus influenzae type b vaccines. First trials along this path are encouraging although, again, group B meningococci pose special problems. The next few years will probably see a new generation of meningococcal vaccines. Generally speaking, the incidence of meningococcal disease is too low to indicate vaccinations for the whole population, or even children, but some risk groups and epidemics are important exceptions. To date, bivalent group A + C or tetravalent group A + C + Y + W135 polysaccharides, or an outer membrane protein-based group B vaccine, are the products to be used when the indications, that may vary from country to country, are considered met. A strong herd immunity effect, demonstrated with group A and C vaccinations, facilitates extinction of an epidemic since large-scale vaccinations can be restricted only in the major risk groups, children and in various schools. Prompt intervention demands, however, a functioning mechanism which detects very early on a pending epidemic. Unfortunately, such a mechanism is often lacking in countries often hit by this deadly disease.