Levels of bactericidal antibodies against meningococcus C after vaccination in 2- to 6-year-old children in Andalusia

BACKGROUND: In 1997, 18.5% of the cases of Meningococcal Disease caused b serogroup C in Andalusia were children between 2 and 4 years of age; ages where the initial immune response and the duration of the capsular A + C meningococcal polysaccharide vaccine is less than in older age groups. Research was designed in order to measure the immune response produced by this vaccine in children from 2 to 6 years of age and to compare it with the natural immunity present in unvaccinated children. METHODS: I. Dual monitoring study: a) groups of children vaccinated previously and control groups, b) groups of children who were going to be vaccinated, for pre and post-vaccination (1, 6 and 12 months) analysis and a control group. II. The bactericidal activity was measured according to the standardised protocol of the CDC with regard to the strain of N. meningitidis C-11. The sera with bactericidal activity (TAB) > 1:8 were considered to be protective. RESULTS: 1 and 2 months following vaccination, the proportion of TAB > 1:8 was significantly higher than that of the control group (65.6% and 73% in comparison to 2.2% and 12%). In the pre-vaccine and post-vaccine (after 6, 7, 12 and 13 months) verification, no significant difference between vaccinated individuals and controls was observed. CONCLUSIONS: The differences between vaccinated and unvaccinated individuals 1 and 2 months following vaccination indicate seroconversion in the vaccinated individuals. For the age group of between 2 to 6 years of age, the bactericidal activity acquired decline quickly, as, after 6 months, differences between this group and the control group are no longer observed. Fundamento: En 1997 el 18,.5% de los casos de Enfermedad Meningccócica por serogrupo C en Andalucía fueron niños de 2 a 4 años de edad; edades donde respuesta inmune inicial y duración de la vacuna antimeningocócica de polisactido capsular A+C, es menor que en eda- des superiores. Se diseñó una investigación para medir la respuesta inmune producida por esta vacuna, en niños de 2 a 6 años de edad, y compararla con la inmunidad natural presente en milos no vacunados. Métodos: 1. Doble estudio de seguimiento: J) grupos de niños previamente vacunados y grupos control, b) grupo de niños que iba a ser vacunado, para análisis pre y postvacunal(l.6 y 12 meses) y grupo control. II.- La actividad bactericida se midió según protocolo estanda- rizado del CDC frente a cepa de N. rnehyírih C-11. Los sueros con título de actividad bactericida (TAB)> 1.8 se consideraron protectores. Resultados: Al mes y a los 2 meses de vacunarse la proporción de TAB>I:B era significativamente superior a la del grupo control (65.5% y 73,9% frente a 2,2% y 12%). En el prevacunal y en el post- vacuna1 a los 6. 7, 12 y 13 meses no se observó diferencia significativa entre vacunados y controles. Conclusiones: Las diferencias entre vacunados y no vacunados 1 y 2 meses después de la vacunación indican seroconversión en los vacu- nados. Para el grupo de edad de 2 a 6 aiios la actividad bactericida adquirida declma rápidamente, ya que a los 6 meses dejan de observarse dife- rencias con el grupo control