Pitisuttithum P, et al. - Considering that using genetically inactivated pertussis toxin (PTgen) may lead to improved immunogenicity of acellular pertussis vaccines and persistence of immunity following vaccination vs using chemically inactivated pertussis toxin (PTchem) because conformational epitopes are preserved, researchers investigated the safety and immunogenicity of two vaccines including PTgen 1 year following vaccination. Outcomes revealed induction of antibody responses that were larger and continued for longer using a monovalent and a combined recombinant acellular pertussis vaccine containing PTgen vs those achieved with the Tdap comparator vaccine. This suggests that the new recombinant pertussis vaccines containing PTgen might have efficacy in limiting pertussis resurgence and can be broadly used, including in pregnant women.

Methods

• In this phase 2/3 non-inferiority, randomized, controlled trial, researchers included 450 adolescents (age 12–17 years) from July 6, 2015 to August 20, 2015.
• Researchers randomized participants 1:1:1 to receive one dose of vaccine containing PTgen and filamentous haemagglutinin (FHA) either in a monovalent formulation (aP_[PTgen/FHA]) or in a combined formulation with tetanus and reduced-dose diphtheria toxoids (TdaP_[PTgen/FHA]) or to receive a commercial vaccine containing reduced-dose PTchem (Tdap) as a comparator.
• Antibody persistence 1 year after vaccination, assessed per protocol in 150 randomly preselected participants (50 per group) was reported as a secondary trial outcome.
• Antibody titres at least four times greater than at baseline defined seroconversion.
• All trial participants were assessed for safety.

Results

• A 1-year follow-up visit was attended by 442 (98%) of 450 enrolled participants between June 5, 2016 and August 9, 2016.
• After 1 year, 38 (76%, 95% CI 64–88) participants in the aP _[PTgen/FHA] group and 41 (81%, 70–92) in the TdaP _[PTgen/FHA] group, but only four (8%, 1–16) in the Tdap comparator group displayed persistent seroconversion for pertussis toxin neutralizing antibodies.
• In the aP _[PTgen/FHA] group (82%, 95% CI 71–93 and 64%, 51–77, respectively) and TdaP _[PTgen/FHA] group (75%, 63–87 and 56%, 42–70, respectively), seroconversion rates for IgG antibodies against pertussis toxin and FHA were also greater than in the Tdap group (4%, 0–9, p<0.0001, and 28%, 16–41, p=0.0007, respectively).
• Twelve participants experienced 13 serious adverse events; all of these were judged to be unrelated to the study vaccines.
• Five pregnancies, reported during follow-up, displayed no maternal or neonatal complications.