Effect of group-A meningococcal vaccine in army recruits in Finland.

During an epidemic caused by group-A, sulphonamide-resistant meningococci in Finland, group-A polysaccharide vaccine was administered in 1974 to 16 458 recruits of the Armed Forces, leaving 20 748 as controls. Specific antibody response was good, and after vaccination only 1% of the men were without anti-meningococcal group-A antibodies. Pharyngeal carriage of the epidemic strain was low, about 1-5%, in the men when entering service. Group-A meningococcal disease occurred during the nine months' mean observation period in 1 of the vaccinated men (an annual incidence of 11 per 100 000) and in 8 of those not vaccinated (71 per 100 000), indicating 89% protective effect of the vaccine. Furthermore, the total number of cases of group-A meningococcal disease was reduced to non-epidemic levels at a time when 36% of the men in service were vaccinated, and has remained low for the next twelve months even though the epidemic in the general population continued.