MENINGITIS OUTBREAKS AND VACCINATION STRATEGY

Three outbreaks of meningitis caused by Neisseria meningitidis serogro up A (subgroup III) are described: Niger (1991), Burundi (1992), and G uinea (1993). These outbreaks showed unusual characteristics: a shorte r inter-epidemic interval (Niger), unusual geographical location outsi de the meningitis belt (Burundi and Guinea), and high age-specific att ack rates in all age groups (Burundi and Guinea). Mass immunization ca mpaigns mobilized considerable human and financial means (US$ 322000 a nd 3000 person-days of work for health personnel to immunize 629 000 p eople in Guinea). The vaccination coverage was over 80% in densely pop ulated areas (Burundi and urban Guinea), bur below 50% in less populat ed areas (24/27 and 26/30 sub-districts in Niger and Guinea, respectiv ely). The preventive fraction (proportion of cases prevented by vaccin ation) was substantial in Guinea (35% for a vaccine efficacy of 85%) a nd was higher where the campaign was initiated earlier. An 'alert' thr eshold indicating the onset of an epidemic of 15/100000 cases in one w eek showed good sensitivity (94%), specificity (98%) and positive pred ictive value (89%) in Burundi, permitting quick decision making outsid e the meningitis belt. These 3 meningococcal meningitis outbreaks show the need for epidemic emergency preparedness and for vigilance on the whole African continent.