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Pneumococcal disease: a summary

  • Invasive pneumococcal disease (e.g. bacteraemia, meningitis) has a high risk of mortality.

  • Pneumococcal disease presents a threat to public health. It can be difficult to diagnose a costly to manage.

  • There are a number of clearly defined risk groups who can be protected by pneumococcal vaccination.

Pneumococcua: diversity of serotypes

  • The system used for classifying serotypes is the Danish numbering system which groups serotypes according to antigenic similarities.

  • Most cases of pneumococcal disease are caused by a minority of the numerous pneumococcal serotypes.

  • The diversity of pneumococcal serotypes is the reason why a vaccine must contain antigens derived from many different serotypes.


Pneumococcal vaccines: antigen composition

  • Cross reactivity within serotypes increases vaccine serotypic coverage by about 80%.

  • A study in France showed that in 1990 at least 90% of the penicillin-resistant isolates (non-invasive and invasive) belonged to serotypes that are incorporated in the 23-valent vaccine.


Pneumococcal vaccines: immune response

  • There is a poor correlation between immunological response and protection, and consensus has been reached on the minimum effective level of antibody required for protection.

  • In common with all polysaccharide vaccines, 23-valent vaccine does not elicit a satisfactory immune response in children aged < 2 years.

  • In HIV-positive patients, the immune response is decreased in those with a CD4+ T cell count <500 cells /µ1 .



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