A genetically inactivated two-component acellular pertussis vaccine, alone or combined with tetanus and reduced-dose diphtheria vaccines, in adolescents: a phase 2/3, randomised controlled non-inferiority trial

Increasing evidence shows that protection induced by acellular pertussis vaccines is short-lived, requiring repeated booster vaccination to control pertussis disease. We aimed to assess the safety and immunogenicity of a recombinant acellular pertussis vaccine containing genetically inactivated pertussis toxin and filamentous haemagglutinin, as either a monovalent vaccine (aP[PTgen/FHA]) or in combination with tetanus and reduced-dose diphtheria vaccines (TdaP[PTgen/FHA]), versus a licensed tetanus and reduced-dose diphtheria and acellular pertussis combination vaccine (Tdap). We did this phase 2/3, randomised controlled non-inferiority trial at two sites in Bangkok, Thailand. Healthy adolescents (aged 12–17 years) were randomly assigned (1:1:1), via a computer-generated randomisation list with block sizes of three, to receive one dose (0·5 mL) of aP(PTgen/FHA), TdaP(PTgen/FHA), or Tdap (comparator). Clinical research staff responsible for participant randomisation, vaccine preparation and administration, and accountability were aware of group allocation. However, allocation was concealed from all other site study staff, data management personnel, statisticians, laboratory staff, and study participants. The primary outcome was non-inferior immunogenicity of TdaP(PTgen/FHA) to Tdap based on seroconversion rates (a four-fold increase or more) for pertussis toxin and filamentous haemagglutinin IgG antibodies 28 days after vaccination, with a predefined 10% margin of equivalence. We did analysis by per protocol. This study is registered with the Thai Clinical Trial Registry, number TCTR20150703002. Between July 6 and Aug 20, 2015, we allocated 450 participants to receive one dose of TdaP(PTgen/FHA) (n=150), aP(PTgen/FHA) (n=150), or comparator Tdap (n=150). 28 days after vaccination, seroconversion rates for anti-pertussis toxin IgG were 96·6% (95% CI 93·8–99·5; n=144) in the TdaP(PTgen/FHA) group and 55·0% (47·1–63·0; n=82) in the comparator Tdap group (difference 41·6%, 95% CI 33·1–50·1; p