KHALIL M1, ALMAZROU Y1, BORROW R2, BALMER P2, BRAMWELL J2, LAL G2,
1 Department of Preventive Medicine, MOH, Saudi Arabia.
2 Meningococcal Reference Unit, HPA North West Laboratory, Manchester, UK.
Meningococcal disease remains a serious public health issue in Saudi Arabia where 4 million
pilgrims visit each year for religious reasons. In response to a shift in prevalence of disease to
those aged under 5 years, a national campaign was conducted in 2003, targeting children from 6
months up to 5 years. Serological responses to the four serogroups included in the
polysaccharide vaccine were evaluated.
Six age groups were included in the study; 6 months (n=43), 12 months (n=45), 18 months
(n=49), 24 months (n=68), 36 months (n=69), and 48 months (n=92). After taking guardian
consent, children were vaccinated with the tetravalent (ACYW135) polysaccharide
meningococcal vaccine, (Mencevax ACWY, GSK). Children 24 months or older were given one
dose while younger children were given two doses with an interval of 2-3 months. Blood
samples were collected before the first dose and one month after the second for children younger
than 24 months and before the single dose and one month after for older children. Serogroup
specific antibody responses were determined by serum bactericidal antibody (SBA) assays using
baby rabbit complement and a tetraplex IgG bead assay.
Pre-vaccination SBA titres increased with age for serogroups A and Y but not for C or W135.
Post-vaccination, for the age bands 6, 12, 18, 24, 36 and 48 months the percentage responders
(SBA titre • 8) were: serogroup A 19, 29, 42, 80, 87, 94, respectively; serogroup C 10, 9, 11, 42,
42, 48, respectively; serogroup W135 12, 13, 18, 48, 55, 62, respectively; serogroup Y 15, 14,
19, 53, 64, 87, respectively. Serogroup-specific IgG levels increased significantly postvaccination
in all age groups except for those aged 6 and 36 months for serogroup C and 6 month
olds for serogroup W135.
To our knowledge, this is the first reported study to evaluate functional antibody responses in
young children following tetravalent polysaccharide vaccination. Two-doses of tetravalent
polysaccharide vaccine in 6,12, and 18 months old children gives poor protection against
serogroups C, Y, and W135. However, for serogroup A, two doses can give 42% responders
(SBA titre • 8) at 18 months of age. A single dose of serogroup A polysaccharide from 2 years
of age gives good protection and a similar level of protection was observed for serogroup Y at 4
years of age but not in younger age groups. However, for serogroups C and W135 poor response
were still evident at 4 years of age.