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Vaccine. 2009 May 21;27(24):3213-22. doi: 10.1016/j.vaccine.2009.03.017. Epub 2009 Mar 26.

Pneumococcal serotype 3 otitis media, limited effect of polysaccharide conjugate immunisation and strain characteristics.

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GlaxoSmithKline Biologicals, Rixensart, Belgium.



In contrast to the other vaccine serotypes, no protection could be demonstrated in the POET study against serotype 3 acute otitis media (AOM) following primary and booster vaccination with a multi-valent pneumococcal conjugate vaccine.


AOM efficacy and immunogenicity data were reviewed. Pheno- and genotypic characteristics of different serotype 3 strains including efficacy study AOM isolates were evaluated.


Evaluation of vaccine efficacy before and after booster vaccination indicated that lack of efficacy against serotype 3 pneumococci might have been due to declined protection following the booster dose. However, although atypical immunogenicity was observed for serotype 3 in the second year of life, the capacity to respond to serotype 3 plain polysaccharide was not impaired. All but one of the serotype 3 strains examined had abundant polysaccharide capsules. Comparison of serotype 3 capsular polysaccharide biosynthesis gene sequences found no relevant differences between any of the serotype 3 strains, but mRNA transcript levels were lower for the less densely encapsulated strain.


Lack of clinical efficacy against serotype 3 AOM following pneumococcal conjugate vaccination may be due to an impaired induction of immune memory. A possible alternative explanation may lie with the atypically abundant expression of capsular polysaccharide which could make serotype 3 strains less susceptible to anti-polysaccharide antibody defence mechanisms in the middle ear. The occurrence of acapsular forms during biofilm growth may also play a role. Clinical impact against otitis media, of vaccines containing pneumococcal serotype 3 components, remains unclear until further investigations have demonstrated the value.

[Indexed for MEDLINE]

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