Ep 214 – Pneumococcal disease

In this episode, Dr Roger Henderson explores pneumococcal disease and the major changes coming to the UK pneumococcal vaccination programme in 2026. Although often overshadowed by other infectious diseases, Streptococcus pneumoniae remains a leading cause of preventable morbidity and mortality worldwide, particularly among older adults, young children and immunocompromised patients. This episode discusses the microbiology and clinical manifestations of pneumococcal disease, reviews the immunological principles behind current vaccines and examines why the UK is transitioning towards the use of the 20-valent pneumococcal conjugate vaccine, or PCV20. It also looks at the wider public health implications of these policy changes and considers how evolving serotype epidemiology continues to shape vaccination strategy in modern clinical practice.

Key take-home points

• Pneumococcal disease is caused by Streptococcus pneumoniae, an encapsulated Gram-positive diplococcus with over 100 serotypes.
• The polysaccharide capsule is the key virulence factor, enabling immune evasion and forming the basis for vaccine design. This structural feature prevents phagocytosis and allows the organism to persist in the host.
• Nasopharyngeal colonisation is common, particularly in children, and is the primary source of transmission.
• Disease ranges from non-invasive infections such as otitis media to invasive pneumococcal disease (IPD) such as meningitis and sepsis.
• IPD represents the most severe end of the spectrum and is associated with significant mortality.
• IPD is defined by isolation of the organism from a normally sterile site and carries high morbidity and mortality.
• Older adults, infants and individuals with chronic disease or immunosuppression are at greatest risk of severe infection.
• Asplenic patients are particularly vulnerable due to impaired clearance of encapsulated organisms. This places them at risk of overwhelming, rapidly progressive sepsis.
• Pneumococcal conjugate vaccines (PCV) induce T-cell dependent immunity, leading to immunological memory and reduced carriage. This contributes not only to individual protection but also to herd immunity at the population level.
• The 23-valent pneumococcal polysaccharide vaccine (PPV23) provides broader serotype coverage than PCV options, but produces weaker, shorter-lived immunity.
• The UK childhood PCV programme has significantly reduced disease burden through both direct protection and herd immunity.
• Serotype replacement remains a key challenge, with non-vaccine serotypes emerging over time. This dynamic shift necessitates ongoing surveillance and periodic vaccine updates.
• Waning immunity and limited booster response have reduced the long-term effectiveness of PPV23 in adults.
• The 2026 UK policy introduces PCV20: a 20-valent PCV that expands serotype coverage while maintaining strong immunogenicity. This represents a shift towards conjugate-based strategies in adult vaccination.
• Adults aged 65 and over and at-risk individuals will receive a single dose of PCV20, replacing PPV23 in most cases.
• Ongoing surveillance is essential to monitor vaccine impact and guide future adaptations in pneumococcal vaccination strategy.

Key references

1. UK Health Security Agency. 2025. https://www.gov.uk/government/publications/pneumococcal-the-green-book-chapter-25.
2. Horn EK, et al. Expert Rev Vaccines. 2021;20(10):1291-1309. doi: 10.1080/14760584.2021.1971521.
3. Falkenhorst G, et al. PLoS One. 2017;12(1):e0169368. doi: 10.1371/journal.pone.0169368.
4. Moreira M, et al. Hum Vaccin Immunother. 2017;13(6):1-12. doi: 10.1080/21645515.2016.1263409.