A phase 2 randomized controlled dose-ranging trial of recombinant pertussis booster vaccines containing genetically inactivated pertussis toxin in women of childbearing age

•Recombinant inactivated pertussis vaccines are safe in non-pregnant women.•Lower-dose genetically-inactivated pertussis toxin has comparable immunogenicity.•Monovalent recombinant pertussis vaccine shows favorable immunogenicity and safety. A phase 2 randomized-controlled safety and immunogenicity trial evaluating different doses of recombinant acellular pertussis vaccine containing genetically-inactivated pertussis toxin (PTgen) was conducted in women of childbearing age in Thailand to identify formulations to advance to a trial in pregnant women. A total of 250 women were randomized 1:1:1:1:1 to receive one dose of one of three investigational vaccines including low-dose recombinant pertussis-only vaccine containing 1 μg PTgen and 1 μg FHA (ap1gen), tetanus, reduced-dose diphtheria (Td) combined to ap1gen (Tdap1gen) or combined to recombinant pertussis containing 2 μg PTgen and 5 μg FHA (Tdap2gen), or one dose of licensed recombinant TdaP vaccine containing 5 μg PTgen and 5 μg FHA (Boostagen®, TdaP5gen) or licensed Tdap vaccine containing 8 μg of chemically inactivated pertussis toxoid (PTchem), 8 μg FHA, and 2.5 μg pertactin (PRN) (BoostrixTM, Tdap8chem). Serum Immunoglobulin G (IgG) antibodies against vaccine antigens were measured before and 28 days after vaccination by ELISA. To advance to a trial in pregnant women, formulations had to induce a PT-IgG seroresponse rate with a 95% confidence interval (95% CI) lower limit of ≥ 50%. Between 5 and 22 July 2018, a total of 250 women with median age of 31 years were enrolled. Post-vaccination PT-IgG seroresponse rates were 92% (95% CI 81–98) for ap1gen, 88% (95% CI 76–95) for Tdap1gen, 80% (95% CI 66–90) for Tdap2gen, 94% (95% CI 83–99) for TdaP5gen, and 78% (95% CI 64–88) for Tdap8chem. Frequencies of injection site and systemic reactions were comparable between the groups. No serious adverse events were reported during the 28-day post-vaccination period. All recombinant acellular pertussis vaccines were safe and immunogenic in women of childbearing age, and all met pre-defined immunogenicity criteria to advance to a trial in pregnant women. Clinical Trial Registration: Thai Clinical Trial Registry, TCTR20180321004.