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Immunogenicity of a 7-valent pneumococcal conjugate vaccine (PCV7) and impact on carriage in Venezuelan children at risk of invasive pneumococcal diseases

Abstract:

Background and aims: We evaluated the immunogenicity of the 7-valent pneumococcal conjugate vaccine (PCV7), and its impact on pneumococcal carriage in Venezuelan children at high risk for invasive pneumococcal disease (IPD). Methods: 82 children (age 2-59 months) with sickle cell anemia (n= 22), chronic heart disease (n= 19), HIV infection (n= 12), immune-suppressive therapy (n= 11) and other IPD-pbkp_redisposing conditions (n= 18) were vaccinated with PCV7 according to CDC-recommended age-related immunization schedules. Blood samples were taken to determine the concentration of IgG antibody, and nasopharyngeal swabs were obtained to isolate Streptococcus pneumoniae, before the first vaccine dose and 1 month after completion of the vaccination schedule. Results: Pneumococcal carriage prior to the first immunization was 27% (n= 22), with the most frequently carried serotypes being vaccine serotypes 6B (22%) and 14 (13%). One month after completion of the vaccination scheme pneumococcal carriage was 22% (n= 17), dominated by non-vaccine serotypes 19A (24%) and 7F (12%). Before immunization, 65% of the subjects had IgG antibody titers >0.35. μg/mL for five serotypes tested. Post-vaccination, 100% of the subjects showed titers >1.0. μg/mL for all PCV7 serotypes with geometric mean concentrations (GMC) ranging from 1.75. μg/mL (serotype 23F) to 17.16. μg/mL (serotype 14). Children previously colonized with serotype 6B had a significantly lower GMC to this serotype following immunization than children not carrying 6B prior to the first PCV dose (p<. 0.05). Conclusions: PCV7 is highly immunogenic in Venezuelan children at high-risk for IPD. Vaccination was associated with an immediate shift in nasopharyngeal carriage toward non-PCV7 serotypes. Finally, we observed serotype-specific hyporesponsiveness to immunization after natural carriage with the same serotype in high-risk children. © 2014 Elsevier Ltd.