Journal of Infection (I984) 9, I97-2o2 EPIDEMIOLOGY Control of epidemic meningococcal meningitis by mass vaccination II. Persistence of antibody four years after vaccination I. Mohammed, G. C. Onyemelukwe, E. N. Obineche, N. Gupta and G. O. Oyeyinka Department of Medicine, Ahmadu Bello University Hospital, Zaria, Nigeria Accepted for publication 26 April I984 Summary Meningococcal antibody was measured in 928 persons vaccinated with combined groups A and C polysaccharide antigens in Bauchi State, Nigeria between 1979 and 1982. Protective amounts of antibody were detected by the indirect haemagglutination technique up to 4 years after vaccination. This persistence was observed mainly in adults, although a substantial proportion of older children also had persistent antibody. Titres in younger children fell progressively, and by the third year the mean log 2 antibody titre was I'4; this may not confer protection against disease. A rational policy for vaccination against meningococcal meningitis would be to revaccinate younger children after 2 years, older children after 4 years, and adults after 6-8 or more years. Introduction Attempts to control epidemic meningococcal disease by vaccinating with univalent or bivalent vaccines have produced largely encouraging results, 1-7 with most epidemics being either prevented or terminated by vaccination. The vaccines used have been shown to be immunogenic in human beings s although less so in younger children2 Antibodies which may confer protection are produced a few weeks after vaccination. 1°-1~ Although high concentrations of antibodies are produced, the duration of protection conferred by vaccination remains unknown. Whereas elevated amounts of group C antibody were found 4 years after immunisation in adult Americans, 13 Greenwood et al. found no appreciable difference in meningococcal antibody concentrations between vaccinated and unvaccinated Nigerians 2 years after the administration of groups A and C vaccines. 14 Mfikel/i (personal communication) has also observed persistence of antibody in Finnish subjects 5 years after vaccination with group B vaccine. There is thus uncertainty about how long vaccination with groups A, B and C polysaccharide vaccines confers protection against meningococcal meningitis, thereby making it impossible to formulate a policy for routine vaccination against the disease. For this reason antibody was measured in subjects vaccinated I-4 years previously in order to see how long protective amounts of antibody persisted. Correspondence and requests for reprints to: Dr I. Mohammed, College of Medicine University of Maiduguri, Nigeria. ox63-4453/84/o5o~97 + 06 $02.00/0 ~) I984 The British Society for the Study of Infection