Duration of the immune response in subjects inoculated with antimeningococcal A and C vaccines kept in storage at -20 degrees C and at 4 degrees C: influence of pre-vaccination titres on the vaccinal response.

The antibody titres in 250 subjects, aged 5 to 22 years, who were vaccinated with a mannitol-lyophilized antimeningococcal A + C vaccine, stable only when stored at -20 degrees C, were followed for two years. As measured by indirect haemagglutination (IHA) and indirect immunofluorescence (IF) techniques, titres for both A and C Neisseria meningitidis antibodies remained high. Two years after vaccination titres of antibodies against type A showed fourfold increase over the initial titres in from 46% to 100% of groups of subjects and against type C in from 42% to 80%.