Toward Universal Protection: A Comprehensive Review of Pneumococcal Disease, Emerging Vaccination Challenges and Future Perspectives

Streptococcus pneumoniae contributes significantly to morbidity, mortality, and healthcare costs worldwide due to severe Invasive Pneumococcal Disease (IPD), particularly among young children and vulnerable populations. This review critically examines the current state of pneumococcal disease epidemiology, the evolution of vaccine strategies, and persistent challenges to achieve global control of the disease. The implementation of Pneumococcal Conjugate Vaccines (PCVs) has yielded substantial public health gains, establishing herd immunity and sharply reducing vaccine-type IPD incidence. However, this success has been fundamentally challenged by serotype replacement, where non-vaccine serotypes have subsequently emerged to cause a significant proportion of the residual disease burden. This epidemiological shift has necessitated the development and deployment of higher-valency PCVs (PCV15, PCV20, and PCV21) to expand serotype coverage. Furthermore, optimal protection requires personalized strategies for high-risk cohorts where vaccine effectiveness can be compromised. In this context, the review details how pneumococcal vaccination - and particularly PPSV23 - serves as an indispensable diagnostic tool to evaluate a broad spectrum of Inborn Errors of Immunity (IEI) and in particular humoral defects. Diagnostic challenges are strained by non-standardized assays and the limited panel of unique serotypes available for testing in the PCV era. The scientific priority is now the development of universal protein-based vaccines, to provide protection against all serotypes and non-encapsulated strains by targeting conserved virulence factors. This integrated approach, combining expanded PCV coverage with novel vaccine technology, is essential to mitigate the ongoing public health burden of pneumococcal disease.