[Effect of 2 vaccination strategies on developments during the epidemic of meningococcal A meningitis in N'Djamena (Chad) in 1988].

From February till May 1988, during an epidemic of group-A meningococcal disease, 4542 cases of meningitis were reported in N'Djamena, the capital of Chad (550,000 inhabitants). A first selective vaccination campaign was carried out between 5 and 14 March; 156,500 vaccine doses (polyvalent: group A and C: Institut Mérieux) were given using jet injectors. The target population for this first campaign consisted of groups such as school-children and the armed forces. As the epidemic continued, a mass vaccination campaign was implemented one month later between 8 and 14 April 1988; this was targeted at the whole population above 1 year of age, not previously immunized, and 266,738 doses of vaccine were injected. One week after the start of the second campaign, the number of reported cases fell sharply and, within four weeks, the epidemic was halted. The vaccination coverage rate, evaluated by a WHO cluster survey method in people above one year of age, was 95.5%. These results show (i) the failure of selective vaccination, restricted to only at-risk groups, to halt the epidemic; (ii) the efficacy of the mass vaccination campaign aimed at the whole population; and (iii) the feasibility in tropical Africa of such a mass campaign which must be carried out in a few days.