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

How to improve pertussis vaccination in pregnancy: a European expert review

INTRODUCTION

Pertussis vaccination in pregnancy is a safe and highly effective strategy to protect young infants against severe pertussis, but cases continue to occur. In November 2023, the authors of this paper met to discuss difficulties faced by pertussis vaccination programs in pregnant women in Europe, and the need and potential for new vaccines.

AREAS COVERED

We summarize current pertussis epidemiology, the status of pertussis vaccination in pregnancy in Europe, followed by a summary of the meeting on benefits of pertussis-only vaccines and pertussis vaccines with improved immunogenicity, including a review of available vaccines.

EXPERT OPINION

Ongoing surveillance and registers documenting vaccine uptake in pregnant women are important to monitor changes in pertussis epidemiology and estimated effectiveness of maternal pertussis vaccination programs in individual countries. While current programs have been effective, Tdap or Tdap-IPV combined vaccines are not the ideal choice but are the only vaccines available for pertussis immunization in pregnancy in Europe. Pertussis-only vaccine would avoid exposing women to unnecessary tetanus and diphtheria boosters in every pregnancy. Recombinant pertussis vaccines with higher immunogenicity could prolong passive immune protection against pertussis in young infants.

Detoxification techniques for bacterial toxins: A pathway to effective toxoid vaccines

Bacterial toxins play a critical role in the virulence of many pathogens, leading to serious diseases such as tetanus, diphtheria, botulism, and entrotoxemia. As key virulence factors, these toxins cause significant tissue damage and disease manifestations in infected hosts. Vaccination against these toxins through toxoid vaccines, composed of inactivated forms of the toxins, represents a vital strategy for preventing toxin-mediated diseases. However, creating effective toxoid vaccines necessitates meticulous detoxification processes that ensure the loss of toxicity while retaining the immunogenic properties inherent in the native toxins. This review offers a comprehensive evaluation of the diverse methodologies employed for detoxifying bacterial toxins, highlighting their advantages, limitations, and implications for vaccine development. By detailing comparisons of efficacy, stability, residual toxicity, and clinical applicability, we demonstrate that while traditional methods utilizing chemical reagents (such as formaldehyde) remain widely used, emerging technologies like genetic inactivation and protein engineering present significant advantages. These innovations promise to advance the development of durable and irreversible toxoid vaccines that protect public health and contribute to future vaccine formulation improvements. Ultimately, this knowledge synthesis aims to guide future research efforts and facilitate the design of safer and more effective toxoid vaccines to combat the public health threats posed by toxin-producing bacteria.

Infant Responses to Primary Immunization Following Vaccination in Pregnancy With Varying Doses of Recombinant Acellular Pertussis Vaccine Alone or Combined With Tetanus-Diphtheria

BACKGROUND

Vaccination in pregnancy with recombinant pertussis vaccine results in similar or higher antibody levels in infants compared with chemically detoxified acellular pertussis vaccine (Tdapchem). We evaluated antibody responses to primary childhood vaccination in infants born to mothers vaccinated in pregnancy with recombinant pertussis vaccine containing 1, 2 or 5 µg genetically detoxified pertussis toxin (ap1gen, Tdap1gen, Tdap2gen or TdaP5gen) or Tdapchem.

METHODS

Infants (393) received diphtheria-tetanus-whole cell pertussis (DTwP) at 2, 4 and 6 months (3+0) and 13-valent pneumococcal conjugate vaccine (PCV13) at 2, 4 and 12 months of age (2+1). Serum IgG levels against pertussis toxoid (PT), filamentous hemagglutinin (FHA), diphtheria toxoid (DT), tetanus toxoid (TT), PCV13 serotypes and PT-neutralizing antibody (PT-Nab) titers were assessed. PT-IgG ≥10 IU was used as a cutoff for potential protection in infants.

RESULTS

PT-IgG geometric mean concentrations (GMC) were ≥10 IU/mL at 5 and 7 months of age but waned below 10 IU/mL at 13 months in all groups. FHA-IgG GMCs and PT-Nab geometric mean titers were also below 10 IU/mL in all groups at 13 months of age. TT-IgG and DT-IgG seroprotection rates (≥0.1 IU/mL) ranged from 97.1% to 100% at 7 and 13 months. Postbooster PCV13-serotype-specific seroprotection rates (IgG ≥ 0.35 µg/mL) ranged between 87% and 100%. Antibody responses were comparable between groups after DTwP priming (7 months) and PCV13 priming (5 months) and booster vaccination (13 months).

CONCLUSIONS

Childhood vaccine responses are comparable after mothers receive genetically or chemically detoxified acellular pertussis vaccines in pregnancy.

Transplacental transfer of maternal antibodies following immunization with recombinant pertussis vaccines during pregnancy: Real-world evidence

AIM/OBJECTIVE

This study investigates placental antibody transfer following recombinant pertussis vaccination in pregnancy in a real-world setting.

METHODS

This postmarketing observational study recruited pregnant women vaccinated with monovalent recombinant acellular pertussis (aP) vaccine (aPgen; n = 199) or combined to tetanus-diphtheria (TdaPgen; n = 200), or Td-vaccine only (n = 54). Pregnancy, delivery, and neonatal outcomes were assessed. Cord blood was collected postdelivery and pertussis toxin (PT)-IgG, filamentous hemagglutinin (FHA)-IgG, and PT-neutralizing antibodies (PT-Nab) were assessed.

RESULTS

No adverse pregnancy, delivery, or neonatal outcomes attributed to aPgen, TdaPgen, or Td vaccination were reported. High anti-PT antibody levels were detected in cord samples from women vaccinated with aPgen (geometric mean concentration [GMC] PT-IgG 206.1 IU/ml, 95% confidence intervals [CI]: 164.3-258.6; geometric mean titer [GMT] PT-Nab 105.3 IU/ml, 95% CI: 81.7-135.8) or TdaPgen (GMC PT-IgG 153.1 IU/ml, 95% CI: 129.1-181.5; GMT PT-Nab 81.5 IU/ml, 95% CI: 66.4-100.0). In the Td-only group, anti-PT antibodies were low (GMC PT-IgG 6.5 IU/ml, 95% CI: 4.9-8.8; GMT PT-Nab 3.8 IU/ml, 95% CI: 2.8-5.1). The same was found for FHA-IgG. Recombinant pertussis vaccination at <27 or 27-36 weeks gestation induced similar cord pertussis antibody levels.

CONCLUSION

This first real-world study confirms that recombinant pertussis vaccination in the second or third trimester of pregnancy results in high levels of passive immunity in infants. Thai Clinical Trial Registry: TCTR20200528006.

Recent development of oral vaccines (Review)

Oral immunization can elicit an effective immune response and immune tolerance to specific antigens. When compared with the traditional injection route, delivering antigens via the gastrointestinal mucosa offers superior immune effects and compliance, as well as simplicity and convenience, making it a more optimal route for immunization. At present, various oral vaccine delivery systems exist. Certain modified bacteria, such as Salmonella, Escherichia coli and particularly Lactobacillus, are considered promising carriers for oral vaccines. These carriers can significantly enhance immunization efficiency by actively replicating in the intestinal tract following oral administration. The present review provided a discussion of the main mechanisms of oral immunity and the research progress made in the field of oral vaccines. Additionally, it introduced the advantages and disadvantages of the currently more commonly administered injectable COVID-19 vaccines, alongside the latest advancements in this area. Furthermore, recent developments in oral vaccines are summarized, and their potential benefits and side effects are discussed.

Effective and safe transfer of maternal antibodies persisting two months postpartum following maternal immunization with different doses of recombinant pertussis-containing vaccines

INTRODUCTION

Recombinant acellular pertussis (ap) vaccines containing genetically inactivated pertussis toxin (PTgen) and filamentous hemagglutinin (FHA) with or without tetanus (TT) and diphtheria (DT) vaccines (Td) were found safe and immunogenic in non-pregnant and pregnant women. We report here maternal antibody transfer and safety data in mothers and neonates.

METHODS

This is the follow up of a phase 2 trial in 2019 among 400 pregnant women who randomly received one dose of recombinant pertussis-only vaccine containing 1 µg PTgen and 1 µg FHA (ap1gen), or Td combined with ap1gen (Tdap1gen), or with 2 µg PTgen and 5 µg FHA (Tdap2gen), or with 5 µg PTgen and 5 µg FHA (TdaP5gen, Boostagen®, BioNet, Thailand) or chemically-inactivated acellular pertussis comparator (Tdap8chem, Boostrix™, GSK, Belgium), either in the second or third trimester of gestation. IgG against PT, FHA, TT and DT were assessed by ELISA, PT-neutralizing antibodies (PTNA) by Chinese Hamster Ovary cell assay and safety outcomes at delivery in mothers and at birth.

RESULTS

Anti-PT and anti-FHA geometric mean concentration (GMC) ratio between infants at birth and mothers at delivery was above 1 in all groups. PT GMC in infants at birth were ≥30 IU/mL in all groups with the highest titers in infants found in TdaP5gen group at birth (118.8 [95% CI 93.9-150.4]). At 2 months, PT GMC ratio to Tdap8chem (98.75% CI) was significantly higher for TdaP5gen (2.6 [1.7-4.0]) and comparable for other recombinant vaccines. No difference in PTNA titers at birth was observed between all groups nor between time of vaccination. Adverse events were comparable in all vaccine groups.

CONCLUSIONS

BioNet licensed (TdaP5gen and Tdap2gen) and candidate vaccines (Tdap1gen and ap1gen) when given to pregnant women in the second or third trimester of gestation are safe and have induced passive pertussis immunity to infants.

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

INTRODUCTION

Despite a decrease in infections caused by Bordetella pertussis due to COVID-19 pandemic, booster vaccination of pregnant women is still recommended to protect newborns. Highly immunogenic vaccines containing genetically inactivated pertussis toxin (PTgen) and filamentous hemagglutinin (FHA) may generate comparable anti-PT antibody concentrations, even at lower doses, to chemically inactivated acellular pertussis vaccines (Tdapchem) shown effective for maternal immunization.

METHODS

This phase 2 randomized, observer-blind, active-controlled non-inferiority trial was conducted in healthy Thai pregnant women randomly assigned to receive one dose of low-dose recombinant pertussis-only vaccine containing 1 µg PTgen and 1 µg FHA (ap1gen), or tetanus, reduced-dose diphtheria combined with ap1gen (Tdap1gen), or combined with 2 µg PTgen and 5 µg FHA (Tdap2gen), or with 5 µg PTgen and 5 µg FHA (TdaP5gen, Boostagen®) or comparator containing 8 µg of chemically inactivated pertussis toxoid, 8 µg FHA, and 2.5 µg pertactin (Boostrix™, Tdap8chem). Blood was collected at Day 0 and Day 28 post-vaccination. The non-inferiority of the study vaccines was assessed based on anti-PT IgG antibody levels on Day 28 pooled with results from a similarly structured previous trial in non-pregnant women.

RESULTS

400 healthy pregnant women received one dose of vaccine. Combined with data from 250 non-pregnant women, all study vaccines containing PTgen were non-inferior to comparator vaccine (Tdap8chem). Both ap1gen and TdaP5gen vaccines could be considered to have superior immunogenicity to Tdap8chem. Local and systemic solicited reactions were similar among all vaccine groups.

CONCLUSIONS

Vaccine formulations containing PTgen were safe and immunogenic in pregnant women. The ap1gen vaccine, with the lowest cost and reactogenicity, may be suitable for use in pregnant women when diphtheria and tetanus toxoids are not needed. This study is registered in the Thai Clinical Trial Registry (www.

CLINICALTRIALS

in.th), number TCTR20180725004.