Immunogenicity, Safety, and Reactogenicity of Concomitant Administration of the Novavax Vaccine against Omicron XBB.1.5 (NVX-CoV2601) and a 20-valent Pneumococcal Conjugate Vaccine in Adults Aged ≥60 Years: A Randomised, Double-blind, Placebo-controlled, Non-inferiority Trial