Background: Maternal immunization with a tetanus, diphtheria and acellular pertussis (Tdap) vaccine may blunt infant pneumococcal immune responses after a primary series of vaccines.
Methods: As part of a prospective controlled cohort trial of Tdap (Boostrix; GSK Biologicals, Rixensart, Belgium) vaccination in pregnancy, infants born to vaccinated mothers and controls were immunized at 8 and 16 weeks and 12 months of age with 13-valent pneumococcal conjugate vaccine (Prevenar13; Pfizer, Wyeth, United States). Sera were tested for pneumococcal antibody concentrations against vaccine serotypes following primary and booster immunization.
Results: Geometric mean concentration of antibodies to serotypes 1, 3, 4, 5, 6A, 7F, 9V, 14 and 19A was significantly lower after 2 doses of Prevenar13 vaccine in the offspring of the mothers vaccinated in pregnancy. This blunting effect disappeared after a booster dose at 12 months of age, except for serotypes 1 and 4. Despite this blunting, the percentage of children achieving the threshold of protection of 0.35 µg/mL was comparable in the vaccine and the control group both after primary and booster vaccination with only a significant lower rate of seroprotection in the vaccine group for serotype 3 after primary vaccination. After booster vaccination, seroprotection rates increased further for serotypes 3, 5, 6B, 9V and 23F.
Conclusions: The present results indicate a blunting effect after primary vaccination for some serotypes resolving after booster vaccination. Seroprotection rates were comparable both after primary and booster vaccination, except for serotype 3 with a significant lower seroprotection rate in the vaccine group after primary vaccination.