Failure of meningococcal vaccination to stop the transmission of meningococci in Nigerian schoolboys. Age-specific differences in duration of clinical protection after vaccination with meningococcal polysaccharide A vaccine. Prevention of secondary cases of meningococcal disease in household contacts by vaccination. Effect of group-A meningococcal vaccine in army recruits in Finland. A controlled field trial of a serogroup A meningococcal polysaccharide vaccine. A serogroup A meningococcal polysaccharide vaccine: studies in the Sudan to combat cerebrospinal meningitis caused by Neisseria meningitidis group A. A second controlled field trial of a serogroup A meningococcal polysaccharide vaccine in Alexandria.
A combined group A and group C meningococcal polysaccharide vaccine was given to 438 Nigerian schoolboys shortly before an outbreak of group A meningococcal disease occurred in their school. Four months after vaccination the carriage rate of group A meningococci among vaccinated subjects (11%) was no different from that found among the controls (12%), although a good antibody response to both components of the vaccine was observed. One case of group A meningococcal disease was recorded amongst 438 vaccinated subjects while five cases occurred among 874 controls. Sequential case-control studies were used to monitor changes in the clinical protection induced by group A meningococcal polysaccharide vaccine over a 3-year period. Overall, vaccine efficacy declined from 87% 1 year after vaccination to 70% and 54% at 2 and 3 years, respectively. When stratified by age at time of vaccination the data showed that, although vaccine efficacy remained high in children greater than or equal to 4 years of age (vaccine efficacy 85%, 74%, and 67% at 1, 2, and 3 years after vaccination, respectively), it declined dramatically in those less than 4 years of age at time of vaccination (vaccine efficacy 100%, 52%, and 8%, respectively, at 1, 2, and 3 years after vaccination). Thus, a single dose of group A meningococcal vaccine does not yield lasting clinical protection in children less than 4 years of age. Household contacts of patients with group A meningococcal infection were vaccinated with either meningococcal vaccine or tetanus toxoid. Five of the 523 subjects who received tetanus toxoid developed meningococcal meningitis and another four probably had meningococcal disease. Only one possible case of meningococcal infection occurred among 520 contacts vaccinated with meningococcal vaccine. Vaccination had no effect on nasopharyngeal carriage of meningococci. Vaccination of household contacts of patients with group A meningococcal infections is an effective way of using limited supplies of meningococcal vaccine, though its value would be limited in an epidemic. Secondary cases of meningococcal infection often occur within a few days of the index case, and, although vaccine alone seemed to provide adequate prophylaxis in these Nigerian subjects, additional chemoprophylaxis may be needed to cover this critical period. 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. A controlled field trial of a serogroup A meningococcal polysaccharide vaccine was conducted at three locations in Egypt during the winter cerebrospinal meningitis (CSM) season of 1971-72. The study population consisted of schoolchildren 6-15 years of age. No cases of serogroup A meningococcal CSM occurred in the group of students vaccinated with the test vaccine whereas 8 cases occurred in the control group vaccinated with tetanus toxoid, and 151 cases occurred in an unvaccinated contrast group. The case rate was significantly different between the test and control groups as well as between the test and contrast groups but was similar between the control and contrast groups. The previously demonstrated safety of the vaccine was confirmed. A significant serological response was elicited in the majority of the vaccinated students. Vaccination against cerebrospinal meningitis (CSM) has regained interest with the use of capsular polysaccharides (or polyosides) of the meningococcus as specific immunizing agents. These compounds proved to be effective in the USA against meningitis caused by Neisseria meningitidis serotype C. This study considers whether the polysaccharides of the serotype A meningococcus, which is prevalent in the African CSM belt, could be protective in epidemic conditions. Taking advantage of the usual seasonal peak of CSM cases, controlled field trials were undertaken in the Sudan early in 1973. 21 640 persons were vaccinated, half of them with a meningococcal polyoside A vaccine and the other half with tetanus toxoid as a placebo. In the former group there were no cases of meningitis, whereas in the latter 10 cases were reported, of which 7 were confirmed by laboratory tests. These studies indicate that the meningococcal polyoside A vaccine is efficient in epidemic conditions and could be used to control outbreaks of meningococcal meningitis. The encouraging results of an earlier controlled field trial of the serogroup A meningococcal polysaccharide vaccine in the prevention of clinical disease prompted this study, the aim of which was to evaluate further the effectiveness of another lot of this type of vaccine, the duration of immunity, and the effectiveness against meningococcal carriage. A controlled field trial was carried out in early 1973 on 176 646 schoolchildren 6-15 years of age, of whom half received the serogroup A polysaccharide vaccine and the other half tetanus toxoid as a control. The incidence of cerebrospinal meningitis caused by serogroup A meningococci was 89% lower in the immunized group than in the controls for one year only. With regard to its effect on carriage, the vaccine was found to reduce to less than half the rate of new acquisition of serogroup A meningococci during the period immediately following immunization. The duration of the carrier state was also shortened in the immunized group.
The  vaccine was strongly protective for the first year in children over five and adults, but its efficacy beyond the first year could not be determined with precision. Children aged one to five years in low-income countries were also protected but the efficacy in this age group could not be determined. While the vaccine was strongly protective among children aged three months to five years in Finland, the efficacy in narrower age strata could not be determined. The sample size was too small to draw conclusions on the effect of booster doses.