Immunogenicity and Safety Study of GSK Biologicals' Quadrivalent Split Virion Influenza Vaccine 2014/2015 Influsplit™ Tetra (Fluarix™ Tetra) (GSK2321138A) When Co-administered With Pneumovax™ 23 in Adults 50 Years of Age and Older

The purpose of this study is to investigate the immunogenicity and safety when GSK Biologicals' influenza vaccine Influsplit™ Tetra (Fluarix™ Tetra) is co-administered with Merck & Co. Inc.'s pneumococcal vaccine (Pneumovax™23/Pneumovax) in adults 50 years of age and older at risk for complications from influenza and pneumococcal infections.