Immune impacts of infant whole-cell and acellular pertussis vaccination on co-administered vaccines

Objectives: We compared the effect of a heterologous wP/aP/aP primary series (hereafter mixed wP/aP) versus a homologous aP/aP/aP primary schedule (hereafter aP-only) on antibody responses to co-administered vaccine antigens in infants and toddlers. Methods: We randomised Australian infants in a 1:1 ratio to receive either a mixed wP/aP schedule (pentavalent diphtheria-tetanus-wP-hepatitis B-Haemophilus influenzae type b; DTwP-HepB-Hib vaccine at 6 weeks old, followed by hexavalent DTaP-inactivated poliovirus vaccine (IPV)-HepB-Hib vaccine at 4 and 6 months old) or aP-only priming doses of hexavalent DTaP-IPV-HepB-Hib vaccine at the same ages. All infants received 13-valent pneumococcal conjugate vaccine (13vPCV) at 6 weeks, 4 and 12 months of age and DTaP-IPV and Hib vaccine boosters at 18 months. We assessed whether the wP/aP schedule is non-inferior to the aP-only schedule for co-administered vaccine antigens (geometric mean ratio [GMR] >2/3). Registration: ACTRN12617000065392p. Results: Between March 2018 and January 2020, 150 infants were randomised (75 per arm). Responses to all 13vPCV serotypes and Hib-PRP at 6, 7, 18, and 19 months old, as well as HBsAg at 6 and 7 months old, were non-inferior (>90% probability). Conclusion: A mixed wP/aP schedule resulted in non-inferior IgG responses to co-administered vaccine antigens compared to the standard aP-only schedule for pertussis primary immunisation.