RESUMEN
Large epidemics of group A meningococcal meningitis occurred in 1995 and 1996 in several countries of the Sub-Saharan Africa zone known as the "meningitis belt", and more particularly in West Africa. Most of these countries affected by the epidemics met difficulties to set up the strategy recommended by the World Health Organization and which includes: Epidemiological surveillance and epidemic incidence threshold calculation to detect early meningitis epidemics and emergency vaccination campaigns with meningococcal A + C polysaccharide vaccine, if possible within the 4-to-6 weeks following the moment the threshold is reached. In this context of epidemics, notably in Mali, and in front of the risk of resurgence of yellow fever, the Ministry of Health of Senegal decided to conduct mass preventive immunization campaigns in 1997 against meningo- coccal meningitis and yellow fever in the districts located in the eastern part of the country and where emergency vaccination would have been difficult in case of epidemic because these area are difficult to reach. A short-term microeconomic evaluation of additional costs that are necessary to organize one of these mass preventive immunization campaigns was conducted in 1997 in the Matam District, in the Northeast part of Senegal. The method rested on value attribution and accounting procedure. The cost was defined as the monetary value of all mobilized resources to product the campaign corresponding to a plurality of charges and representing all of the effective expenses and donations. During this campaign, 85,925 people were vaccinated and a total number of 163,981 doses of both polysaccharide A + C meningococcal and yellow fever vaccines were administered within 3 weeks. Four intervention strategies were involved: Three for vaccination (mobile, fixed and outreach strategy) and one for coordination, information and training. The total cost of the campaign was 55,322.75 euros. Vaccines and solvents represented 60% of the total cost of the campaign, materiel for injection and safety of injection 26%, vaccination staff 7%, and logistics 7%. The mean cost was 0.34 euro per administered dose and 0.64 euro per vaccinee. The mean cost per administered dose of meningococcal vaccine was 0.44 euro. The mean cost of preventive meningococcal immunization was not higher than the mean cost of meningococcal vaccination during mass emergency immunization campaigns in other countries. The addition of yellow fever antigen brought down the campaign mean cost by 0.11 euro and it allowed economies of scales. Direct unit costs per administered dose were higher when people were vaccinated through the outreach strategy (0.35 euro) than when fixed and mobile strategies were used (0.318 and 0.323 euro, respectively). Costs related to transportation and staff were proportionally higher for the outreach strategy. Direct unit costs per administered dose were higher when vaccinations were done in rural areas (0.32 euro) than when done in urban areas (0.31 euro). Direct unit costs increased when the size of target communities decreased (in communities with less than 100 people to vaccinate versus 0.38 euro in communities with more than 2,000 people to vaccinate). This study allowed us to set up a method to measure, describe and analyze the costs of a mass preventive campaign. It demonstrated the economic impact of using multiple antigens during a single preventive campaign.