Keywords
Streptococcus pneumoniae
Invasive Pneumococcal Disease
Epidemiological surveillance
Abstract
S. pneumoniae has been classified by the World Health Organization (WHO) as one of the 12 priority pathogens with the greatest global health impact. Although many individuals (approximately 20–30% of adults and nearly 40–50% of children) may carry the bacterium asymptomatically, certain groups are considered at higher risk of disease (non-invasive illnesses and invasive diseases). These include young children, the elderly and individuals who are immunocompromised or affected by pre-existing medical conditions.
Italian surveillance data show a significant increase in Invasive Pneumococcal Disease (IPD) incidence in 2023 in comparison with 2021 and 2022, rising from 0.84 cases per 100,000 population in 2021 to 3.02 in 2023. The highest rates were observed in children under 1 year of age [10.41/100,000 (2023)] and in adults aged 65 and over (7.45/100,000 in 2023 compared with 2.11 in 2021 and 4.49 in 2022).
Surveillance systems and epidemiological studies on the global distribution of the different pneumococcal serotypes associated with disease continue to be essential to determining which serotypes to include in new vaccines, in order to produce preparations capable of preventing an increasing number of cases, hospitalizations, sequelae and deaths.
A milestone in pneumococcal vaccination was the development of conjugate vaccines (PCVs), which started in the 2000s. The first PCV, which covered seven serotypes (PCV7: 4, 6B, 9V, 14, 18C, 19F, and 23F), was introduced in Italy in 2005 for the pediatric population. The introduction of this vaccination strategy leading to a significant reduction in disease among children and an overall decline in the pneumococcal disease burden across all age-groups. However, an increase in disease caused by serotypes not included in PCV7 was observed. This phenomenon, named serotype replacement, led to the development of higher-valency conjugate vaccines. In 2010, the 13-valent pneumococcal vaccine (PCV13) and 10-valent pneumococcal vaccine (PCV10) were approved. However, the phenomenon of serotype replacement continued to be observed, and consequently, the need for broader-spectrum vaccines remained a public health priority.
In 2021 and 2022 PCV15 (serotypes: 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 22F, 23F and 33F) and PCV20 (serotypes: 1, 3, 4, 5, 6A, 6B, 7F, 8, 9V, 10A, 11A, 12F, 14, 15B, 18C, 19A, 19F, 22F, 23F and 33F) were authorized for immunization in individuals aged ≥18 years, respectively. In March 2025, the use of a new 21-valent pneumococcal vaccine was approved (serotypes: 3, 6A, 7F, 19A, 22F, 33F, 8, 10A, 11A, 12F, 9N, 17F, 20, 15A, 15C, 16F, 23A, 23B, 24F, 31 and 35B) and it included some serotypes particularly aggressive or emerging.
Maximizing the effectiveness of a vaccination program in combating diseases related to S. pneumoniae is based on the integration of three key elements: epidemiological need, immunological need and vaccine compliance.
From an epidemiological perspective, the 2023 specific data analysis reveals that, out of 1,783 cases, 734 involved individuals over the age of 64 (41.2%). The estimated coverage with the PCV20 vaccine would be 63.6%, while with the PCV21 vaccine it would be 76.4%. The specific analysis of the most recent available data (1st half of 2024) reveals that a total of 1,152 cases were reported, 58.4% of which occurred in individuals over 64. If only the data referring to subjects over the age of 64 are analyzed, the estimated coverage becomes 72.1% for PCV20 and 79.2% for PCV21.
From an immunological standpoint, the vaccine should induce an immune response that is at least non-inferior to the comparator, and ideally, robust and long-lasting.
Regarding compliance, all possible strategies must be activated in order to raise awareness of the risks of pneumococcal disease and the benefits of vaccination, so as to increase coverage rates.
A thorough analysis of epidemiological and clinical data, combined with an assessment of the economic and social impact, is crucial to guiding vaccination policies and supporting efficient decision-making in order to protect the health of the entire population.
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