Seroconversion and duration of immunity after vaccination against group C meningococcal infection in young children

An increase in the incidence of group C meningococcal disease was observed in the Murcia Region (Spain) during 1996-1997. In September 1997, a massive vaccination campaign was implemented among the population aged 18 months to 19 years. The aim of this study was to assess the seroconversion rate of children aged 18-59 months and the persistence of immune response 1 year after vaccination. A total of 296 children were included. Blood samples were obtained before vaccination and 1 month and 1 year after vaccination. Three point seven percent of the children had bactericidal antibody titres of >/=1:8 before vaccination. One month after vaccination seroconversion was 63.7%, with a growing trend related to age at vaccination (p<0.0001). The increase in antibody titres was shown to be quantitatively greater above the age of 36 months (p<0.0001). One year after vaccination only 4.3% of the children who initially seroconverted still had bactericidal activity. Seroconversion in children under 5 increases with age but antibodies decline rapidly in the year following vaccination.