N. Meningitis
A quadrivalent meningococcal polysaccharide vaccine, which protects against disease caused by serogroups A, C, W-135 and Y, is recommended for travellers to the areas within the ‘meningitis belt’ of Africa as well as travellers to the religious festivals of Hajj and Umra (see section on incidence). Travellers to these festivals must ensure their vaccination covers these four meningococcal serogroups, as Saudi authorities request a certificate of vaccination from visiting pilgrims. However, although polysaccharide vaccines do provide protection they have drawbacks as they are not effective in children less than 2 years of age and offer only short-term protection (3–5 years).
Vaccine immunogenicity is greatly improved by chemical conjugation of the polysaccharide antigen to a protein carrier (either detoxified diphtheria toxoid [CRM197] or tetanus toxoid). Conjugated vaccines can be used to immunise infants and induce long-term immunological protection. Effective conjugate vaccines against meningococcal serogroup C (MenC) are available, and cases of meningitis caused by MenC have fallen dramatically in countries implementing routine MenC vaccination schedules, leading to a reduction in the number of cases of Group C disease by around 95% in all age groups. In the UK vaccination is carried out in infants 3 and 4 months of age with a booster dose at 12 months of age1. Immunisation with MenC conjugate vaccine induces herd immunity, and so protects unvaccinated individuals living within a largely vaccinated population.
Other conjugate vaccines, incorporating polysaccharide antigens from serogroups A, C, W-135 and Y, and therefore providing greater protection against meningococcal disease, are currently in development. It is hoped that these vaccines will provide broad, long-term protection against meningococcal disease.
In contrast to serogroups A, C, W-135 and Y, there is no routine vaccine against meningococcal serogroup B (MenB). This is because the polysaccharide capsule of MenB is poorly immunogenic and cross-reacts with sialylated proteins in human tissues. Vaccine research against serogroup B meningococcus has therefore focused mainly on outer membrane proteins, particularly the protein PorA. MenB disease has been a particular problem in New Zealand and monovalent PorA and hexavalent PorA vaccines, against the New Zealand MenB strain, have been developed using recombinant technology. However, there is as yet no vaccine against other MenB strains.
Reference:
1. NHS. A guide to childhood immunisations for babies up to 13 months of age. Available at: http://www.immunisation.nhs.uk/files/275774_Babies.pdf. (Accessed April 2007)
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