Pneumonia and Invasive Pneumococcal Diseases: The Role of Pneumococcal Conjugate Vaccine in the Era of Multi-Drug Resistance

Abstract

Streptococcus pneumoniae related diseases are a leading cause of morbidity and mortality, especially in children and in the elderly population. It is transmitted to other individuals through droplets and it can spread to other parts of the human host, causing a wide spectrum of clinical syndromes, affecting between 10 and 100 cases per 100,000 people in Europe and the USA. In order to reduce morbidity and mortality caused by this agent, pneumococcal vaccines have been developed over the years and have shown incredible effectiveness in reducing the spread of this bacterium and the development of related diseases, obtaining a significant reduction in mortality, especially in developing countries. However, considerable problems are emerging mainly due to the replacement phenomenon, multi-drug resistance, and the high production costs of conjugated vaccines. There is still a debate about the indications given by various countries to different age groups; this is one of the reasons for the diffusion of different serotypes. To cope with these problems, significant efforts have been made in the research field to further improve vaccination serotypes coverage. On the other hand, an equally important commitment by health care systems to all age group populations is needed to improve vaccination coverage.

Keywords: anticapsular antibodies; humoral immunity; pneumococcal colonization; pneumonia; serotypes; vaccines.

Figure 1

Schematic representation of the T-indipendent mechanism of the PPV 23 vaccine. Polysaccharide antigens, such as pneumococcal antigens contained in PPV23, stimulate pre-existing memory B cells (MBC) towards terminal differentiation into antibody-producing cells.

Figure 2

Schematic representation of the T-dependent mechanism of the PCV 13 vaccine. The polysaccharidic portion of PCV stimulates the production of plasma cells, while the carrier portion of PCV activates CD4+ T lymphocytes that induces memory B cell proliferation and long-lived plasma cells.