It is increasingly understood that acellular pertussis vaccines are associated with rapid waning of vaccine-induced immune responses and a consequent rise in pertussis disease several years after vaccination [[1],[2]]. All acellular pertussis vaccines contain inactivated pertussis toxin (PT) and most include one up to four additional pertussis antigens (filamentous hemagglutinin, FHA; pertactin, PRN; and fimbriae type 2 and 3, FIM2/3). PT-specific antibodies with toxin-neutralising properties are essential and sufficient to prevent severe pertussis disease [[3],[4]]. To ensure vaccine safety, pertussis toxin must be inactivated for use in humans. In most acellular pertussis vaccines this is accomplished using chemical processes that not only inactivate the toxin but also affect conformational epitopes inducing neutralising antibodies [[5],[6]]. In adolescents vaccinated in childhood with acellular pertussis vaccines containing chemically inactivated PT (PTchem), booster vaccination with a PTchem containing vaccine has been demonstrated to provide moderate protection against pertussis during the first year but then to wane rapidly so that little protection remained 2–3 years after booster vaccination [[7]]. In contrast to chemical inactivation, genetic inactivation preserves the native epitope structures and immunogenic properties of PT that are important to induce a neutralising antibody response [[4],[5]], and hence may induce longer lasting protection.
A new generation acellular pertussis vaccine containing genetically detoxified PT (PTgen) was developed and licensed as a monovalent recombinant acellular pertussis vaccine (aPgen) or combined with tetanus and reduced-dose diphtheria toxoids (TdaPgen), for immunisation of individuals aged 11 years and older in Thailand [[8],[9]]. Both formulations are used in Thailand to vaccinate adolescents and adults, including pregnant women and the elderly, against pertussis [[10]]. Pivotal booster vaccination studies in adolescents in Thailand and Switzerland have demonstrated that compared to chemically detoxified pertussis booster vaccine (Tdapchem), aPgen and TdaPgen are more immunogenic and induce PT-specific IgG and PT neutralising antibody responses that persist to be significantly higher 1 year after vaccination [[11],[12]]. To demonstrate that the superior immune responses induced by these new generation recombinant acellular pertussis vaccines last longer, we compared the persistence of vaccine antibody responses in adolescents 2 and 3 years after booster vaccination with one dose of the new generation recombinant PTgen containing pertussis vaccines (aPgen or TdaPgen) or a booster dose of a Tdapchem vaccine.
Source : EClinicalMedicine
