Conference Coverage

New acellular pertussis vaccine may solve waning immunogenicity problem



– A novel, monovalent, acellular pertussis vaccine containing a recombinant, genetically inactivated pertussis toxin displayed markedly greater sustained immunogenicity than the widely used Sanofi Pasteur Tdap, known as Adacel, which is used as a booster vaccination of adolescents and young adults, in a pivotal phase 3, randomized trial, Simonetta Viviani, MD, reported at the annual meeting of the European Society for Paediatric Infectious Diseases.

Jacopo Werther/Wikimedia Commons/Creative Commons Attribution 2.0
A Tdap containing the same proprietary genetically detoxified pertussis toxin (PT) also outperformed the conventional, acellular pertussis–containing Adacel in the pivotal three-arm study. Both novel vaccines were similar to Adacel in terms of safety. Based on these results, the novel monovalent vaccine, known as Pertagen, and the novel Tdap, known as Boostagen, are now licensed and marketed in Thailand.

“Our interpretation of these results is that they open up a new way to approach pertussis vaccination,” declared Dr. Viviani, director of clinical development at BioNet-Asia, a Bangkok-based biotech vaccine company.

The impetus for developing new acellular pertussis vaccines is the documented resurgence of pertussis.

“One suggested approach has been to replace chemically inactivated PT with a genetically inactivated PT. The rationale for that is the epitopes of the PT are conserved in the genetically modified PT toxin, as opposed to being destroyed in the chemical inactivation process,” Dr. Viviani explained.

The significant phase 3 trial included 450 Thai 12- to 17-year-olds who were randomized to a single 0.5-mL dose of Pertagen, Boostagen, or Adacel. Both Pertagen and Boostagen contain 5 mcg of the genetically inactivated PT and 5 mcg of filamentous hemagglutinin.

The seroconversion rate, defined as the proportion of subjects who reached at least a fourfold increase in titers of PT and filamentous-hemagglutinin antibodies over baseline, was far superior at both 28 days and 1 year in subjects who got Pertagen or Boostagen, compared with those who received Adacel.

Dr. Simonetta Viviani Bruce Jancin/Frontline Medical News

Dr. Simonetta Viviani

The fast-waning immunity that is a major limitation of conventional acellular pertussis vaccines was amply illustrated by the difference in falloff of PT-neutralizing antibody over time. The PT-neutralizing antibody titer was 278 IU/mL at 1 month and 77 IU/mL at 1 year in the Pertagen group, 216 IU/mL at 1 month and 67 IU/mL at 1 year with Boostagen, and a mere 36 IU/mL at 1 month and 12 IU/mL at 1 year with Adacel.

Session chair Ulrich Heininger, MD, declared, “This is really, really exciting.”

It now will be very important that the monovalent Pertagen vaccine be formally studied in pregnant women, he observed.

“Since we’d like to immunize women in every pregnancy and they don’t necessarily need the Td component of Tdap every time, a monovalent vaccine might open a new path for acceptance,” commented Dr. Heininger, professor of pediatric infectious diseases at University Children’s Hospital in Basel, Switz.

Dr. Viviani said that a study in pregnant women is now in the early planning stages.

The study was sponsored by BioNet-Asia and Mahidol University. Dr. Viviani is a BioNet employee.

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