Immunogenicity and safety of an inactivated quadrivalent influenza vaccine co-administered with a 23-valent pneumococcal polysaccharide vaccine versus separate administration, in adults ≥50 years of age: Results from a phase III, randomized, non-inferiority trial

•Co-administration of IIV4 with PPV23 was compared with separate administration.•Immunological non-inferiority of co-administration was shown for IIV4 and PPV23.•Both vaccines had an acceptable safety and reactogenicity profile.•Co-administration of PPV23 at annual influenza vaccination visits may help uptake.•High-risk comorbidities had no impact on IIV4 immunogenicity.