Pneumococcal antibodies in a child with type 14 pneumococcal conjugate vaccine failure

We measured the concentration, opsonic activity, and avidity of serotype-specific serum antibodies in a pneumococcal conjugate vaccine (PnCRM7) efficacy trial participant who contracted serotype 14 pneumococcal bacteremia following dose 3 of PnCRM7. Controls included 18 PnCRM7- and 10 MnCC-vaccinated children without invasive pneumococcal disease (IPD). The child with vaccine failure had 4.98 mcg/mL of serotype 14 antibodies 10 days before disease onset; these antibodies had greater opsonic activity and lower avidity than those of control PnCRM7 recipients. The child had no booster response to a fourth dose of PnCRM7 for most vaccine serotypes. We conclude that antibody concentration, functional activity and avidity do not predict individual protection against IPD, and immunological correlates of protection are only useful at the population level.