Vann, W. previously required that pilgrims attending either Hajj or Umra be vaccinated with the bivalent A/C polysaccharide vaccine (4), and a monovalent serogroup A vaccine was required for children less than 2 years of age. Due to the change observed in the period from 2000 to 2002, the Saudi Ministry of Health recommended the use of the tetravalent ACYW135 polysaccharide vaccine to provide coverage against serogroup W135 for pilgrims and Saudi school children. Further analysis revealed that 58% of reported meningococcal disease was in children less than 5 years of age and 39% was in those below 2 years of age (3). Hence, the Ministry of Health initiated an immunization program in 2003 to vaccinate children Rabbit polyclonal to PNPLA8 from 6 months to 5 years of age. However, the immunogenicity of the tetravalent ACYW135 polysaccharide vaccine in these age groups was unknown. A follow-up study was performed to assess the serologic responses of children 5 years old to meningococcal tetravalent ACYW135 polysaccharide vaccine (2). Children less than 18 months old received two doses 2 to 3 3 months apart, and those 24 months old received one dose. Poor serum bactericidal antibody (SBA) responses were observed to the serogroup C, W135, and Y components of the vaccine in children 18 months old, whereas 42% of children had SBA titers of 8 for serogroup A. In children 2 years old, 80% had SBA titers of 8 for serogroup A, with a similar number observed for serogroup Y for children 4 years of age. However, poor responses to serogroup C and W135 were still observed for children 4 years of age. As a result of this study, the use of the tetravalent polysaccharide vaccine in children 2 years old has been discontinued in Saudi Arabia. The study also exhibited that responses to meningococcal polysaccharides are both age and polysaccharide dependent, with serogroup A polysaccharide being more immunogenic in younger children, confirming previous reports (5, 8, 12). It is well known that this immune systems of young children cannot process polysaccharide PX-866 (Sonolisib) antigens in a manner appropriate for stimulating an effective response, but it is usually unclear at what age the immune system is usually mature enough to provide the PX-866 (Sonolisib) correct environment for this process. Hence, a study was performed with Saudi children 5 to 9 years of age to ensure that the responses to the tetravalent ACYW135 polysaccharide vaccine merited the continuation of its use in this age group. Two hundred forty-one children were recruited to the study from Qassim Province and were split into the following age groups: 5 years old (= 47), 6 years old (= 45), 7 years old (= 49), 8 PX-866 (Sonolisib) years old (= 50), and 9 years old (= 50). Each group received one dose of Mencevax ACWY (GSK, Rixensart, Belgium), and blood samples were obtained from each child prior to and 1 month after vaccination following agreement to participate by the child’s guardian. Serogroup-specific antibody responses were determined by SBA assays as previously described (11) by using the same meningococcal strains as those in the previous study of Saudi children 5 years old (2). Serogroup-specific immunoglobulin G (IgG) levels were determined using a tetraplex bead assay as previously described (9). Unlike the previous report of responses in Saudi children 5 years old (2), there was no age-dependent trend observed for either the SBA responses or the IgG concentrations, and hence all age groups have been combined and results presented for each individual serogroup. The numbers of individuals with SBA titers of 8 for before and after vaccination and 4-fold increases in SBA titers from before vaccination to after vaccination are given in Table ?Table1.1. Forty percent of children had SBA titers of 8 for serogroup A, and 55% had comparable titers for serogroup Y before vaccination. Significant increases in the numbers of individuals with SBA titers of 8 from.