Using meningococcal polysaccharide vaccines to contain epidemics

WHO recommends mass vaccination of the population over the age of one year with either the bivalent (serogroup A/C) or trivalent (A/C/135) meningococcal polysaccharide vaccine, based on the predominant serogroup causing the epidemic (A,C or W135), when the number of cases of meningococcal meningitis in a district has passed a defined threshold. This requires an active surveillance system which is now in place in many countries in the meningitis belt.

Provided that polysaccharide vaccines are deployed promptly they can halt an epidemic and save many lives but widespread use of polysaccharide vaccines has not prevented epidemics of meningococcal disease in the meningitis belt. This failure is due to the fact that polysaccharide vaccines are not very immunogenic in young children, induce only transitory protection in this age group, do not induce immunological memory and have little impact on carriage (and hence on transmission) of the infection (except possibly in military populations where some reduction in carriage following vaccination has been observed).

Mali rural clinic. © Stuart J.