Following acellular pertussis vaccination during pregnancy, antibody concentrations in cord blood to vaccine antigens, including pertussis toxin (PTx), filamentous haemagglutinin (FHA) and pertactin (Prn), are increased in the infant, and to concentrations greater than or equal to those in the mother 11, due presumably to active transport of antibodies across the placenta 12. Here, CIAO3 is linked to pertussis.