Efectivity y and Duration of the Immunity of the Serogroups A and C Meningococcal Vaccine

Abstract

BACKGROUND: In 1995 the Community of Madrid detected an increase in the number of cases of meningococcal disease caused by serogroup C. In 1997 a mass vaccination campaign was carried out in relation to the population between 18 months and 19 years of age. The purpose of this study is to ascertain the immune response produced by the vaccine and its relationship to the age of the subjects. METHODS: A sample group of 1,003 children vaccinated during the campaign was selected. A blood sample was extracted prior to vaccination and after one, six (only <5a) and twelve months had transpired. In order to assess the immune response, the levels of bactericidal and total antibodies were measured. RESULTS: The prevalence of seroconversion measured by bactericidal antibodies is 89.6%. The response is low in children under 3 (34.8%), increases with age and, from 7 years on, surpasses the 90% mark. After 6 months, the prevalence of protective levels in children under 5 years of age drops noticeably (31.3%). After one year, the prevalence drops significantly, particularly in children under 7 years of age. The proportion of individuals with total antibody response after one month is over 90%, and remains high after one year in all of the age groups (97.5%). CONCLUSIONS: The response measured by means of total antibodies contradicts the clinical response to the vaccination and the measurement by means of bactericidal antibodies underestimates the protection if it is compared with the results of vaccinal efficacy, for which reason, we need to search for biological indicators that would correlate adequately with the clinical response following immunisation.