Abstract:
Background: In developing countries, introduction of pneumococcal conjugate vaccine
has not eliminated circulation of vaccine serotypes. Vaccinating pregnant mothers to
increase antibody concentrations in their newborn infants may reduce the acquisition of
pneumococcal carriage and subsequent risk of disease. We explored the efficacy of
passive immunity, attributable to anti-protein and anticapsular pneumococcal antibodies,
against acquisition of carriage.
Methods: We examined the rate of nasopharyngeal acquisition of pneumococci in the
first 90 days of life associated with varying anticapsular and anti-protein antibody
concentrations in infant cord/maternal venous blood in Kilifi, Kenya. We used
multivariable Cox proportional hazard models to estimate continuous functions relating
acquisition of nasopharyngeal carriage to the concentration of maternally derived
antibody.
Results: Cord blood or maternal venous samples were collected from 976 mother-infant
pairs. Pneumococci were acquired 561 times during 33,905 person-days of follow-up.
Increasing concentrations of anti-protein antibodies were associated with either a
reduction (PhtD1, PspAFam2, Spr0096, StkP) or, paradoxically, an increase (CbpA,
LytC, PcpA, PiaA, PspAFam1, RrgBT4) in acquisition rate. We observed a
nonsignificant reduction in the incidence of homologous carriage acquisition with high
concentrations of maternally derived anticapsular antibodies to 5 serotypes (6A, 6B, 14,
19F, and 23F).
Conclusion: The protective efficacy of several anti-protein antibodies supports the
strategy of maternal vaccination to protect young infants from carriage and invasive
disease. We were not able to demonstrate that passive anticapsular antibodies were
protective against carriage acquisition at naturally occurring concentrations though it
remains possible they may do so at the higher concentrations elicited by vaccination.