The persistence of antibodies induced by meningococcal polysaccharides of groups A and C in human volunteers

Ninety-nine college students (58 males and 41 females) aged 17 to 23 years were each injected subcutaneously with 50 μg of meningococcal polysaccharides A and C. Titrations of antisera obtained at various time intervals during the two subsequent years were made by passive haemagglutination microtitration using human O Rh-negative red blood cells from a single source. The percentage of responders (those who developed a fourfold increase in titre) to polysaccharide A was 97.9% and that to polysaccharide C was 94.8%. Pre-immunization titres of 16 to polysaccharide A and 8 to polysaccharide C were considered to be threshold values above which the response might be impaired. There was a significant (P < 0.01) difference in the geometric mean HA titre between vaccinees and control groups after vaccination at each time interval studied. The majorities of both the vaccinees and the controls had a higher peak titre to polysaccharide A than to polysaccharide C.