A high attack rate (17·3/100 000) of meningococcal disease in army recruits in Italy, with 95% of the cases due to serogroup C, constituted the motivating factors to make bivalent serogroup A + C meningococcal vaccination compulsory by law for army recruits starting January 1987. Because the vaccine was given only to the new recruits entering the army, full coverage was not achieved until January 1988. Nearly 900 000 subjects (300 000 yearly) were vaccinated between January 1987 and December 1989. There were no reports of any untoward reactions to the vaccine. Of the 300 000 recruits in service each year, 52, 21, 15, 5 and 4 cases of the disease occurred in 1985, 1986, 1987, 1988 and 1989, respectively (P < 0·001).
Of the 24 cases occurring since the start of the vaccination, only two (due to serogroup C) were attributable to vaccine failure. The remaining cases were in unvaccinated recruits (15 cases) or were due to serogroups other than A or C (7 cases). The cumulative incidence of meningococcal serogroup C in the 600 000 vaccinated recruits during the period 1988–89 was 0·2/100 000 (1 case amongst 600 000 recruits), while the corresponding figure in the 600 000 unvaccinatred recruits during the period 1985–6 was 11·3/100000 (68 cases amongst 600 000 recruits) (P < 0·001). The protective efficacy of the vaccine in 1987 was 91·2% (12 cases of meningococcal serogroup A and C disease from an average of 150 000 unvaccinated recruits observed for 1 year, and 1 case from the corresponding average of 150 000 vaccinated ones). In 1988 and in 1989 this figure could not be calculated because all recruits were vaccinated.
The incidence of meningitis caused by other serogroups of meningococci remained low, both before and after the mass vaccination campaign.