Why are PCV vaccines recommended to be given first when a patient is getting both a PCV and PPSV23 vaccines? Wouldn’t PPSV23 protect them against additional strains of the pneumococcal bacteria?

PCV vaccines are recommended to be given first because this sequence provides the best immune response to both PCV and PPSV23 vaccines. An evaluation of immune response after a second pneumococcal vaccination administered 1 year after an initial dose showed that subjects who received PPSV23 as the initial dose had lower antibody responses after subsequent administration of PCV13 than those who had received PCV13 as the initial dose followed by a dose of PPSV23.