The numbers 20 and 23 in pneumococcal vaccine names indicate covered serotypes, not an automatic ranking of effectiveness. PCV20 is a conjugate vaccine, while PPSV23 is a polysaccharide vaccine, and they stimulate immunity differently. The Korean Society of Infectious Diseases’ 2025 guidance offers a single PCV20 dose or PCV15 followed by PPSV23 for adults aged 65 and older and high-risk adults. Previous vaccination and underlying conditions affect the product and interval, so consultation should include vaccination records. Pneumococcal prevention does not protect against pneumonia caused by every bacterium or virus.