Capsule switching among C:2b:P1.2,5 meningococcal epidemic strains after mass immunization campaign, Spain.

A mass immunization campaign for 18-month to 19-year-olds was undertaken in Spain in 1996-1997 because of an epidemic of serogroup C meningococcal disease associated with a C:2b:P1.2,5 strain belonging to the A4 lineage. Surveillance for the "capsule-switching" phenomenon producing B:2b:P1.2,5 isolates was undertaken. Of 2,975 meningococci characterized, B:2b:P1.2,5 and B:2b:P1.2 antigenic combinations were found in 18 isolates; 15 meningococci were defined as serogroup B belonging to the A4 lineage.