Maternal pneumococcal conjugate immunization protects infant chinchillas in the pneumococcal otitis media model

Abstract

Infant immunization with pneumococcal polysaccharide-protein conjugate vaccines (PCVs) is unlikely to elicit protective serum antibody concentrations during the first 4-6 months of life, when recurrent pneumococcal otitis media (POM) often begins. We therefore investigated a maternal pneumococcal immunization strategy to prevent early infant POM. Pregnant chinchillas (dams) received injections of heptavalent PCV or saline. Post-partum maternal and infant (kits) blood samples were obtained, and kits were subsequently challenged by intranasal inoculation of a vaccine-type pneumococcal strain (19F). Anti-pneumococcal capsular polysaccharide IgG antibody (Ab) concentration was measured using an ELISA in maternal and kit serum samples. Immunized dams and their kits had significantly higher Ab titers than control dams and their kits. Antibody titer in kits declined with a half-life of 12 days. Maternal immunization significantly reduced both the incidence (p = 0.05) and severity (p <0.01) of experimental POM in chinchilla kits, and was 82% effective at preventing mortality from invasive pneumococcal disease. Pre-challenge serum Ab concentration in kits was the single best predictor of POM severity (r = -0.66). This experiment strongly supports the hypothesis that maternal immunization with PCV will reduce the burden of early infant POM and invasive pneumococcal disease.