The effect of meningococcal group A and C polysaccharide vaccine on nasopharyngeal carrier state.

The effect of Neisseria meningitidis group A and C polysaccharide vaccine on nasopharyngeal carriage was studied in Italian army recruits. Throat swabs were cultured for N. meningitidis at the time of vaccination (one week after entry to service) and again three weeks later in a follow-up cohort of 98 men. At the first survey the overall carriage rate was 32% with 9% of isolates due to serogroup C, none to serogroup A and 17% to serogroup Y. At the second survey the overall carriage rate reached 52% (P less than 0.01); no isolate belonged to serogroup A or C, while serogroup Y reached 40% (P less than 0.01). The cumulative carriage rate was 65%. Out of the 64 carriers during the whole study period, only 7 (11%) belonged to the same serogroup during the two different surveys. The vaccination appears to influence the carriage rate of meningococcal specific serogroups. The inhibition of serogroups A and C is, however, offset by an increased prevalence of meningococci belonging to serogroup Y.