Is group-specific meningococcal vaccination resulting in epidemics caused by groups of virulent meningococci?

In 1976 routine vaccination against Neisseria meningitidis serogroups A and C was started in the Finnish Armed Forces. A case of fulminant, complicated pneumonia caused by group-Y meningococcus in a vaccinated recruit, prompted a study of the distribution of the meningococcal groups isolated from the recruits in the same unit. 14 (46%) of the 31 isolates from 84 recruits were group Y. Group-Y meningococcus was rarely isolated from unvaccinated controls. These results suggest that widespread vaccination against serogroups A and C may have led to an increase in the frequency of meningococcus group Y.