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


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


RESULTS
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.


CONCLUSIONS
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.
Poolman
Jan
J
GlaxoSmithKline Biologicals, Rixensart, Belgium. jan.poolman@gskbio.com
Kriz
Pavla
P
Feron
Christiane
C
Di-Paolo
Emmanuel
E
Henckaerts
Isabelle
I
Miseur
Agnes
A
Wauters
Dominique
D
Prymula
Roman
R
Schuerman
Lode
L
D000328:Adult; D001402:B-Lymphocytes / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007114:Immunization; D007156:Immunologic Memory; D010033:Otitis Media / Q000382:microbiology / Q000517:prevention & control*; D010587:Phagocytosis; D022242:Pneumococcal Vaccines / Q000276:immunology*; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification*
D022242:Pneumococcal Vaccines