Difference

Pneumococcal Plain Polysaccharide Vaccine and Conjugate Vaccine

Case-control and observational studies provide the majority of information pertaining to the protection afforded by PPSV23. Lower efficacy was reported in a widely referenced case control study in the United States of 983 IPD cases in which PPSV23 demonstrated 61% efficacy (95% CI, 47-72) in immunocompetent adults.¹ In immunocompromised persons, the vaccine-type efficacy was much lower at 21% (95% CI, −55 to 60) and not statistically significant.²

Polysaccharide vaccines generally induce only short-term immunity, and do not elicit memory-boosting responses, and are not effective in the elicitation of immune responses in children aged <2 years. These characteristics are associated with an immune response elicited primarily by B-cells in secreting IgM.³

In this type of a response, polysaccharide(s) interact directly with B-cells and activate them expressing surface IgM antibodies specific to pneumococcal serotype-specific polysaccharide(s). The response to pneumococcal polysaccharides is independent of the dedicated antigen
presenting cells or T lymphocyte help. The absence of their involvement prevents the induction of an IgM to IgG antibody switch and the formation of memory B-cells (see figure below).³​​

Differences Between Plain Polysaccharide and Protein-polysaccharide Conjugate Vaccines^4-6,7-9

CI, confidence interval; IPD, invasive pneumococcal disease; IgG, immunoglobulin G; IgM, immunoglobulin M; PPSV23, 23-valent pneumococcal plain polysaccharide vaccine.

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