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Published online by Cambridge University Press: 25 March 2010
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°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%.
For 130 subjects vaccinated with a new lactose–lyophilized antimeningcoccal A + C vaccine (presumed stable at 4°C) antibody titres were measured up to 16 months after inoculation with this vaccine stored at −20°C and also after storage for several periods at 4°C. Antibody titres in all these subjects had fallen to their initial titres by 16 months.
The importance of evaluating the results on subjects showing low initial titres (≤1/8 as measured by IHA) is discussed, as inclusion of high initial titres influences the extent of the response.