Immunization with the heptavalent pneumococcal conjugate vaccine in Bangladeshi infants and effects of zinc supplementation

Background: Zinc deficiency is known to impair immunologic functions. However, the effect of zinc supplementation on immune response to polysaccharide vaccines is not known. Objective: To determine the immunogenicity of the heptavalent Pneumococcal protein conjugate (PNC) vaccine in poor Bangladeshi infants and to assess the effect of zinc supplementation on immune response to the PNC vaccine. Design: We immunized a sub-cohort of 241 infants who had previously received three doses of a Hib conjugate vaccine with three doses of the heptavalent PNC vaccine at 4 weeks intervals beginning at 18 ± 1 weeks of age. The infants were supplemented with daily 5 mg zinc or placebo from 4 to 33 weeks of age. Response to each of the seven PNC serotypes were assessed at 4, 24 and 33 weeks of age. Results: After three doses of PNC, at 29 weeks of age, geometric mean titres for the pneumococcal serotypes ranged from 3.68 to 13.34 μg/ml. Titres were significantly higher for infants who had received PNC compared to infants who had only received DTP-Hib. Zinc supplementation resulted in higher titres for serotype 9V (4.09 μg/ml; [95% CI: 3.27; 5.10] and 3.33 μg/ml; [95% CI: 2.79; 3.96] for zinc and placebo group, respectively; p < 0.05) after three doses but had no effect on other serotypes. Conclusions: A heptavalent PNC vaccine proved to be safe and immunogenic in Bangladeshi infants. Zinc supplementation enhanced the immune response to only one of the serotypes (9V). However, there was no effect on other serotypes.