The serotype-specific efficacy and immunogenicity of a 9-valent pneumococcal conjugate vaccine determined during an efficacy trial in The Gambia, West Africa

Abstract number: P1334

Okoko J., Saaka M., Kohberger R.C., Biney E., Enwere G., Zaman A., Goldblatt D., Cutts F., Greenwood B.M., Adegbola R.A.

Background: A large randomised, double-blind, placebo-controlled vaccine trial in The Gambia showed that a 9-valent pneumococcal conjugate vaccine (PCV-9) had high efficacy against radiological pneumonia and invasive pneumococcal disease of vaccine serotype and reduced substantially hospital admissions and child mortality. Here, we report post vaccination pneumococcal antibody concentration in a nested subsample of infants who participated in this trial.

Methods: A single 2–4 ml venous blood specimen was collected from 213 4–6 weeks Gambian children after the third dose of vaccine or placebo and tested by ELISA for type-specific IgG antibodies to pneumococcal serotype 1, 4, 5, 6B 9V 14 18C, 19F and 23F polysaccharides. And from the main trial, we performed per-protocol and intention-to-treat analyses to assess the serotype specific vaccine efficacy.

Results: Geometric Mean Concentrations (GMCs) were significantly higher for each serotype in children receiving three doses of PCV-9 than those in placebo group. Among PCV-9 recipients, GMCs ranged between 2.61 and 11.09 mg/ml with the highest being against serotype 14 and the lowest against 9V. Point estimates of the proportion of infants with post vaccination antibody concentrations geqslant R: gt-or-equal, slanted0.15 mg/ml, geqslant R: gt-or-equal, slanted0.35 or geqslant R: gt-or-equal, slanted1.0 mg/ml ranged from 97.9% – 100%, 92.9% – 100% and 83.9% – 95.8%, respectively, for individual polysaccharides. In contrast, only 9.6% – 39.0%, 7.2% – 20.9% and 1.1% – 10.1% of infants in the placebo group attained these antibody concentrations. The estimated overall protective level for all the 9 serotypes, based on the vaccine efficacy against vaccine type specific invasive pneumococcal disease of 77% (95% CI: 51, 90) observed in the whole trial, was 2.3 mg/ml(95% CI: 1.0, 5.0).

Conclusion: The 9-valent pneumococcal conjugate vaccine studied was immunogenic in a Gambian population where it was also found to be efficacious

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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