Vaccine immunogenicity Blood samples will be collected pre-vaccination, 2 months and 12 months post-vaccination for 7 pneumoccocal serotypes (4, 6B, 9V, 14, 18C, 19F, 23F). Samples will be centrifuged and serum will be frozen and stored at −70 ◦C until tested. In order to eliminate non-specific antibodies that may exhibit cross-reactivity, the samples will be pre-absorbed with the C-polysaccharide and with the heterologous serotype 22F.