This study aims to evaluate the safety, reactogenicity and immunogenicity of GlaxoSmithKline (GSK) Biologicals´ 10-valent pneumococcal conjugate vaccine when co-administered with diphtheria, tetanus, acellular pertussis-hepatitis B virus-inactivated polio virus/Haemophilus influenzae type b (DTPa-HBV-IPV/Hib) vaccine in preterm infants as a 3-dose primary immunization course during the first 6 months of life.