Safety and immunogenicity of a trivalent recombinant PcpA, PhtD, and PlyD1 pneumococcal protein vaccine in adults, toddlers, and infants: A phase I randomized controlled study

•This phase I study examined a candidate trivalent pneumococcal protein vaccine.•The vaccine contained recombinant PcpA, PhtD, and PlyD1.•The vaccine was safe and immunogenic in adults, toddlers, and infants.•In infants, aluminum adjuvant improved immunogenicity without changing safety.•The results support and provide guidance for the development of the vaccine.