The 20-Valent Pneumococcal Conjugate Vaccine (PCV20): A Comprehensive Review of Clinical Evidence, Regulatory Status, and Public Health Implications

Section 1: Introduction: The Evolving Strategy for Pneumococcal Disease Prevention

1.1 The Enduring Burden of Streptococcus pneumoniae

Streptococcus pneumoniae remains a formidable global pathogen and a leading cause of morbidity and mortality across all age groups. This bacterium is responsible for a wide spectrum of clinical disease, from relatively mild mucosal infections to life-threatening invasive pneumococcal diseases (IPD).[1] IPD, which includes conditions such as meningitis, bacteremia, and sepsis, carries a high risk of severe outcomes, including long-term neurological sequelae and death.[2] Non-invasive manifestations, while less severe, constitute a massive public health burden; pneumococcal pneumonia is a primary cause of hospitalization, and otitis media is one of the most common reasons for pediatric physician visits and antibiotic prescriptions.[4]

The global impact of pneumococcal disease is substantial. In older adults, pneumococcal pneumonia is estimated to cause approximately 30 million episodes and 500,000 deaths annually.[6] In children, S. pneumoniae is a principal cause of bacterial pneumonia and a significant contributor to global child mortality.[4] The risk of severe disease is not uniformly distributed. The highest burden falls on the very young (infants under 5 years), older adults (aged 50 and over), and individuals of any age with underlying chronic medical conditions or immunocompromise. At-risk conditions include chronic heart, lung, liver, or kidney disease; diabetes; and conditions that weaken the immune system.[7]

1.2 The Immunological Divide: From Polysaccharide to Conjugate Vaccines