It was unknown if giving a 23-valent pneumococcal polysaccharide vaccine (PPSV23) and quadrivalent influenza vaccination (QIV) at the same time induced immunogenicity in older people. For a study, researchers wanted to determine if the pneumococcal antibody response evoked by simultaneous administration of PPSV23 and QIV in older people was inferior to that generated by sequential administration of PPSV23 and QIV. Researchers conducted a single-center, randomized, open-label, non-inferiority study with 162 persons aged equal and above 65 randomly allocated to either the simultaneous (PPSV23 and QIV injected simultaneously) or sequential (PPSV23 administered 2 weeks after QIV immunization) groups. IgG titers against pneumococcal serotypes 23F, 3, 4, 6B, 14, and 19A were measured. 

The primary outcome was the response rate to serotype 23F (a≥2-fold rise in IgG concentrations 4–6 weeks after PPSV23 immunization). With the non-inferiority margin established at 20% fewer patients, the response rate of serotype 23F in the concurrent group (77.8%) was not inferior to that of the sequential group (77.6%; difference, 0.1%; 90% CI, -10.8% to 11.1%). 4–6 weeks after immunization, there were no significant differences in pneumococcal IgG serotype titers across groups. Other than B/Texas, simultaneous dosing did not result in a substantial decrease in seroprotection odds ratios for H1N1, H3N2, or B/Phuket influenza viruses. 

As a result, simultaneous administration of PPSV23 and QIV showed comparable immunogenicity to sequential treatment without an increase in adverse events. Furthermore, concurrent administration did not affect adverse effects.