Long-term (three-month and one-year) follow-up of nasopharyngeal carriers of Neisseria meningi- tidis with a frequency of sample collection of once a week and once a month resp. in the healthy population with a mean age of 43 years revealed a 4.8% positivity (2 of 42 subjects). Carriership of the same phenotype and ET-genotype of the N. meningitidis group 29E was stable in one subject, while the other long-term carrier of N. meningitidis group B has changes of the phenotype as well as ET-genotype during the follow-up period. Double (after a 3-month interval) verification of the seroprevalence of specific antimeningococcal antibodies revealed in a group of immunized subjects (vaccine A and C) a considerable degree of anti A immunity. Anti A-seropositivity in subjects immunized within a three-year interval since vaccination was 100%, in those immunized within a four-year interval a decline to 66% was recorded. Anti C antibodies after vaccination within a three-year interval were recorded in 75% subjects, in vaccinated subjects the authors detected antibodies during the first year after vaccination in 86% of the subjects. Natural anti A antibodies of the lowest titre 1:6 were recorded in four non-vaccinated subjects (22%). Naturally acquired anti B antibodies (B:2a:P1.2,P1.5) and anti C (C:2a:P1.2,P1.5) were not detected in any of the subjects.

        Key words: Neisseria meningitidis – long-term carriership – seroprevalence of specific antibodies.