Boosting Teenagers With Acellular Pertussis Vaccines Containing Recombinant or Chemically Inactivated Pertussis Toxin: A Randomized Clinical Trial

A reduced-dose recombinant pertussis vaccine booster in Thai adolescents: a phase 2/3, observer-blinded, randomised controlled, non-inferiority trial

BACKGROUND

A resurgence of pertussis has increased the demand for low-cost vaccines. The aim of this study was to test the immunogenicity of a booster acellular monovalent pertussis vaccine containing reduced-dose (2 μg) recombinant pertussis toxin (PT) and 5 μg filamentous haemagglutinin (FHA; apgen) against a version of apgen containing tetanus and reduced-dose diphtheria toxoids (Tdapgen) and a licensed vaccine containing chemically detoxified PT and FHA combined with tetanus toxoid and reduced-dose diphtheria toxoid (Tdapchem).

METHODS

This phase 2/3, observer-blinded, randomised, controlled, non-inferiority trial was done in adolescents aged 9-17 years at two clinical research centres in Bangkok and Pathum Thani, Thailand. Eligible participants were screened and randomly assigned (1:1:1) to receive one booster dose of apgen, Tdapgen, or Tdapchem vaccine. Participants were followed up until day 336 post-immunisation. The primary endpoint was non-inferior seroconversion rates in Tdapgen and Tdapchem vaccine groups, with seroconversion rate defined as the proportion of participants with at least a four-fold increase on day 28 post-immunisation relative to baseline of anti-PT and anti-FHA IgG. The non-inferiority for seroconversion rates of anti-PT and anti-FHA IgG was defined as the lower bound of the two-sided 95% CI of the seroconversion rate for Tdapgen compared with Tdapchem exceeding -10%. Immunogenicity was analysed in the per-protocol population. All safety data were collected, and the prevalence of adverse events was analysed in the intention-to-treat population. This trial was registered on the Thai Clinical Trial Registry (TCTR20181031001).

FINDINGS

Between June 18, and Aug 3, 2019, 450 adolescents (mean age 12·1 years, SD 2·5) were enrolled and randomly assigned (150 participants in each group). Day 28 anti-PT IgG seroconversion rates were 141 (94%) of 150 participants who received Tdapgen (95% CI 88·8-97·0) and 105 (71%) of 149 participants who received Tdapchem (62·7-77·2; p<0·0001). Day 28 anti-FHA IgG seroconversion rates were 144 (96%) of 150 participants who received Tdapgen (91·4-98·3) and 124 (83%) of 149 participants who received Tdapchem (76·4-88·4; p<0·0001). The difference in seroconversion rates was 23·5% (95% CI 15·3-31·8) for anti-PT IgG and 12·8% (6·0-19·6) for anti-FHA IgG, when comparing the Tdapgen versus the Tdapchem vaccine group. No vaccine-related serious adverse events were reported.

INTERPRETATION

Recombinant Tdapgen vaccine showed non-inferior immunogenicity compared with Tdapchem at day 28 in terms of seroconversion rate of anti-PT IgG and anti-FHA IgG relative to baseline. The reduced-dose approach for Tdapgen vaccines thus presents as a potentially cost-saving booster strategy to protect adolescents against pertussis.

FUNDING

Office of National Higher Education Science Research and Innovation Policy Council (Programme Management Unit Competitiveness), Thailand, and BioNet-Asia.

Antibody and B-cell Immune Responses Against Bordetella Pertussis Following Infection and Immunization

Neither immunization nor recovery from natural infection provides life-long protection against Bordetella pertussis. Replacement of a whole-cell pertussis (wP) vaccine with an acellular pertussis (aP) vaccine, mutations in B. pertussis strains, and better diagnostic techniques, contribute to resurgence of number of cases especially in young infants. Development of new immunization strategies relies on a comprehensive understanding of immune system responses to infection and immunization and how triggering these immune components would ensure protective immunity. In this review, we assess how B cells, and their secretory products, antibodies, respond to B. pertussis infection, current and novel vaccines and highlight similarities and differences in these responses. We first focus on antibody-mediated immunity. We discuss antibody (sub)classes, elaborate on antibody avidity, ability to neutralize pertussis toxin, and summarize different effector functions, i.e. ability to activate complement, promote phagocytosis and activate NK cells. We then discuss challenges and opportunities in studying B-cell immunity. We highlight shared and unique aspects of B-cell and plasma cell responses to infection and immunization, and discuss how responses to novel immunization strategies better resemble those triggered by a natural infection (i.e., by triggering responses in mucosa and production of IgA). With this comprehensive review, we aim to shed some new light on the role of B cells and antibodies in the pertussis immunity to guide new vaccine development.

Novel approaches to reactivate pertussis immunity

INTRODUCTION

Whole cell and acellular pertussis vaccines have been very effective in decreasing the deaths of neonates and infants from Bordetella pertussis. Despite high vaccine coverage worldwide, pertussis remains one of the most common vaccine-preventable diseases, thus suggesting that new pertussis vaccination strategies are needed. Several candidates are currently under development, such as acellular pertussis vaccines that use genetically detoxified pertussis toxin, acellular pertussis vaccines delivered with new adjuvants or new delivery systems, or an intranasally delivered, live attenuated vaccine.

AREAS COVERED

This review discusses the different possibilities for improving current pertussis vaccines and the present state of knowledge on the pertussis vaccine candidates under development.

EXPERT OPINION

Until there is a safe, effective, and affordable alternative to the two types of existing vaccines, we should maintain sufficient childhood coverage and increase the vaccination of pregnant women, adolescents, and young adults.

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

BACKGROUND

A phase 2 randomized-controlled safety and immunogenicity trial evaluating different doses of recombinant acellular pertussis vaccine containing genetically-inactivated pertussis toxin (PTgen) was conducted in women of childbearing age in Thailand to identify formulations to advance to a trial in pregnant women.

METHODS

A total of 250 women were randomized 1:1:1:1:1 to receive one dose of one of three investigational vaccines including low-dose recombinant pertussis-only vaccine containing 1 μg PTgen and 1 μg FHA (ap1gen), tetanus, reduced-dose diphtheria (Td) combined to ap1gen (Tdap1gen) or combined to recombinant pertussis containing 2 μg PTgen and 5 μg FHA (Tdap2gen), or one dose of licensed recombinant TdaP vaccine containing 5 μg PTgen and 5 μg FHA (Boostagen®, TdaP5gen) or licensed Tdap vaccine containing 8 μg of chemically inactivated pertussis toxoid (PTchem), 8 μg FHA, and 2.5 μg pertactin (PRN) (BoostrixTM, Tdap8chem). Serum Immunoglobulin G (IgG) antibodies against vaccine antigens were measured before and 28 days after vaccination by ELISA. To advance to a trial in pregnant women, formulations had to induce a PT-IgG seroresponse rate with a 95% confidence interval (95% CI) lower limit of ≥ 50%.

RESULTS

Between 5 and 22 July 2018, a total of 250 women with median age of 31 years were enrolled. Post-vaccination PT-IgG seroresponse rates were 92% (95% CI 81-98) for ap1gen, 88% (95% CI 76-95) for Tdap1gen, 80% (95% CI 66-90) for Tdap2gen, 94% (95% CI 83-99) for TdaP5gen, and 78% (95% CI 64-88) for Tdap8chem. Frequencies of injection site and systemic reactions were comparable between the groups. No serious adverse events were reported during the 28-day post-vaccination period.

CONCLUSIONS

All recombinant acellular pertussis vaccines were safe and immunogenic in women of childbearing age, and all met pre-defined immunogenicity criteria to advance to a trial in pregnant women.

CLINICAL TRIAL REGISTRATION

Thai Clinical Trial Registry, TCTR20180321004.

The History of Pertussis Toxin

Besides the typical whooping cough syndrome, infection with Bordetella pertussis or immunization with whole-cell vaccines can result in a wide variety of physiological manifestations, including leukocytosis, hyper-insulinemia, and histamine sensitization, as well as protection against disease. Initially believed to be associated with different molecular entities, decades of research have provided the demonstration that these activities are all due to a single molecule today referred to as pertussis toxin. The three-dimensional structure and molecular mechanisms of pertussis toxin action, as well as its role in protective immunity have been uncovered in the last 50 years. In this article, we review the history of pertussis toxin, including the paradigm shift that occurred in the 1980s which established the pertussis toxin as a single molecule. We describe the role molecular biology played in the understanding of pertussis toxin action, its role as a molecular tool in cell biology and as a protective antigen in acellular pertussis vaccines and possibly new-generation vaccines, as well as potential therapeutical applications.

Evaluation of Anti-PT Antibody Response after Pertussis Vaccination and Infection: The Importance of Both Quantity and Quality

Pertussis toxin (PT) is considered the main virulence factor causing whooping cough or pertussis. The protein is widely studied and its composition was revealed and sequenced already during the 1980s. The human immune system creates a good response against PT when measured in quantity. However, the serum anti-PT antibodies wane rapidly, and only a small amount of these antibodies are found a few years after vaccination/infection. Therefore, multiple approaches to study the functionality (quality) of these antibodies, e.g., avidity, neutralizing capacity, and epitope specificity, have been investigated. In addition, the long-term B cell memory (Bmem) to PT is crucial for good protection throughout life. In this review, we summarize the findings from functional PT antibody and Bmem studies. These results are discussed in line with the quantity of serum anti-PT antibodies. PT neutralizing antibodies and anti-PT antibodies with proper avidity are crucial for good protection against the disease, and certain epitopes have been identified to have multiple functions in the protection. Although PT-specific Bmem responses are detectable at least five years after vaccination, long-term surveillance is lacking. Variation of the natural boosting of circulating Bordetella pertussis in communities is an important confounding factor in these memory studies.

Antibody persistence 2 and 3 years after booster vaccination of adolescents with recombinant acellular pertussis monovalent aPgen or combined TdaPgen vaccines

BACKGROUND

Recombinant pertussis vaccines inducing long-lasting immune responses could help to control the rise in pertussis. We here report on persisting antibody responses 2 and 3 years after booster vaccination with a new generation recombinant acellular pertussis vaccine.

METHODS

Participants of a phase 2/3 randomised-controlled clinical trial with a monovalent pertussis vaccine containing genetically inactivated pertussis toxin (aPgen) or its tetanus and diphtheria toxoids combination (TdaPgen), or a chemically detoxified comparator vaccine (Tdapchem), (originally conducted between July and August 2015) were invited to participate in observational studies of persisting antibody responses 2 and 3 years after vaccination. Serum IgG against pertussis toxin (PT-IgG) and filamentous hemagglutinin (FHA-IgG) were assessed by ELISA, and PT-neutralising antibodies (PT-Nab) by Chinese Hamster Ovary cell assay.

FINDINGS

Waning of antibodies stabilised in aPgen and TdaPgen vaccinees 2 and 3 years after vaccination. Three years post-vaccination PT-neutralising antibodies remained 4·6-fold (95% Confidence Interval (CI) 2·6-8·1) and 3·7-fold (95% CI 2·2-6·1) higher, PT-IgG antibodies 3·0-fold (95% CI 2·2-4·1) and 2·5-fold (95% CI 1·9-3·3) higher, and FHA-IgG antibodies 1·8-fold (95% CI 1·3-2·5) and 1·6-fold (95% CI 1·2-2·1) higher than baseline in aPgen and TdaPgen recipients, respectively. In the Tdapchem group, PT-neutralising and PT-IgG and FHA-IgG antibodies were back at baseline levels 2 years post-vaccination. Three years post-vaccination seroconversion rates for PT-neutralising antibodies were 65·0% (95% CI 44·1-85·9) and 55·0% (95% CI 33·2-76·8) in aPgen and TdaPgen recipients, respectively.

INTERPRETATION

Considering the persistence of elevated antibody responses 3 years post-booster vaccination, genetically detoxified monovalent aPgen and TdaPgen vaccines can be expected to induce longer-lasting protection than chemically inactivated Tdap vaccines.

FUNDING

BioNet-Asia.

Immunological Distinctions between Acellular and Whole-Cell Pertussis Immunizations of Baboons Persist for at Least One Year after Acellular Vaccine Boosting

While both whole-cell (wP) and acellular pertussis (aP) vaccines have been highly effective at reducing the global pertussis disease burden, there are concerns that compared to wP vaccination, the immune responses to aP vaccination may wane more rapidly. To gain insights into the vaccine elicited immune responses, pre-adult baboons were immunized with either aP or wP vaccines, boosted with an aP vaccine, and observed over a nearly two-year period. Priming with a wP vaccine elicited a more Th17-biased response than priming with aP, whereas priming with an aP vaccine led to a more Th2-biased response than priming with wP. These differences were maintained after aP vaccine boost immunizations. Compared to aP, animals primed with a wP vaccine exhibited greater numbers of pertussis specific memory B cells. While aP and wP vaccine priming initially elicited similar levels of anti-pertussis toxin antibody, titers declined more rapidly in aP vaccine primed animals leading to a 4-fold difference. Both wP and aP vaccine immunization could induce serum bactericidal activity (SBA); however, only one wP vaccine immunization was required to elicit SBA while multiple aP vaccine immunizations were required to elicit lower, less durable SBA titers. In conclusion, when compared to aP vaccine, priming with wP vaccine elicits distinct cellular and humoral immune responses that persist after aP vaccine boosting.

Acellular Pertussis Vaccine Inhibits Bordetella pertussis Clearance from the Nasal Mucosa of Mice

Bordetella pertussis whole-cell vaccines (wP) caused a spectacular drop of global pertussis incidence, but since the replacement of wP with acellular pertussis vaccines (aP), pertussis has resurged in developed countries within 7 to 12 years of the change from wP to aP. In the mouse infection model, we examined whether addition of further protective antigens into the aP vaccine, such as type 2 and type 3 fimbriae (FIM2/3) with outer membrane lipooligosaccharide (LOS) and/or of the adenylate cyclase toxoid (dACT), which elicits antibodies neutralizing the CyaA toxin, could enhance the capacity of the aP vaccine to prevent colonization of the nasal mucosa by B. pertussis. The addition of the toxoid and of the opsonizing antibody-inducing agglutinogens modestly enhanced the already high capacity of intraperitoneally-administered aP vaccine to elicit sterilizing immunity, protecting mouse lungs from B. pertussis infection. At the same time, irrespective of FIM2/3 with LOS and dACT addition, the aP vaccination ablated the natural capacity of BALB/c mice to clear B. pertussis infection from the nasal cavity. While wP or sham-vaccinated animals cleared the nasal infection with similar kinetics within 7 weeks, administration of the aP vaccine promoted persistent colonization of mouse nasal mucosa by B. pertussis.

Enhanced post-licensure safety surveillance of a new recombinant acellular pertussis vaccine licensed as a monovalent (aP, Pertagen®) and tetanus, reduced-dose diphtheria combination (TdaP, Boostagen®) vaccine for immunization of adolescents and adults in Thailand

A new generation of recombinant acellular pertussis vaccine containing genetically inactivated pertussis toxin (PTgen) was licensed as a monovalent pertussis vaccine (aP_gen; Pertagen®) and in combination with tetanus and reduced-dose diphtheria (TdaP_gen; Boostagen®) for active immunization in individuals aged 11 years and older in Thailand in 2016. We here report post-marketing safety data on the use of the vaccines in individuals in the community obtained through active pharmacovigilance surveillance including pregnant women participating in a prospective observational study. Between May 2017 and February 2020 for TdaP_gen and between June 2018 and February 2020 for aP_gen, participating health care providers vaccinated and collected safety data for 11,429 exposed adolescents and adults. This included 1778 pregnant women. The incidence rate of adverse events following immunization (AEFIs) was 11.5 per 1000 of vaccinated individuals (95% confidence interval (95% CI) 9.7-13.6). AEFIs mostly concerned local pain at the injection site and muscle pain, and symptoms were mild and mostly resolved within a few days with no complications. The incidence rate of AEFIs in women vaccinated during pregnancy was 1.1 per 1000 (95% CI 0.3-4.1). Of 833 pregnant women vaccinated with recombinant aP_gen or TdaP_gen, 91.4% (95% CI 89.3-93.3) had uncomplicated pregnancies and 98.7% (95% CI 97.7-99.4) of the 855 babies delivered by these women were born healthy, which exceeds rates generally reported in Thailand. There were no vaccine-related serious adverse events reported during the surveillance period. In conclusion, active pharmacovigilance confirms that the recombinant pertussis vaccines aP_gen (Pertagen) and TdaP_gen (Boostagen) are safe in adolescents and adults, including pregnant women vaccinated in the second or third trimester of pregnancy.

Safety and immunogenicity of the epicutaneous reactivation of pertussis toxin immunity in healthy adults: a phase I, randomized, double-blind, placebo-controlled trial

OBJECTIVES

Protection induced by acellular vaccines can be short, requiring novel immunization strategies. Objectives of this study were to evaluate safety and capacity of a recombinant pertussis toxin (PTgen) -coated Viaskin® epicutaneous patch to recall memory responses in healthy adults.

METHODS

This double-blind, placebo-controlled randomized trial (Phase I) assessed the safety and immunogenicity of PTgen administered on days 0 and 14 to healthy adults using Viaskin® patches applied directly or after epidermal laser-based skin preparation. Patch administration was followed by Boostrix®dTpa on day 42. Antibodies were assessed at days 0, 14, 28, 42 and 70.

RESULTS

Among 102 volunteers enrolled, 80 received Viaskin-PT (Viaskin-PT 25 μg (n = 25), Viaskin-PT 50 μg (n = 25), laser + Viaskin-PT 25 μg (n = 5), laser + Viaskin-PT 50 μg (n = 25)), Viaskin-placebo (n = 10) or laser + Viaskin-placebo (n = 2). Incidence of adverse events was similar across groups (any local event: 21/25 (84.0%), 24/25 (96.0%), 4/5 (80.0%), 24/25 (96.0%), 8/10 (80.0%), 10/12 (83.0%), respectively). Direct application induced no detectable response. On day 42, PT-IgG geometric mean concentrations were significantly higher following laser + Viaskin-PT 25 μg and 50 μg (139.87 (95% CI 87.30-224.10) and 121.76 (95% CI 95.04-156.00), respectively), than laser + Viaskin-placebo (59.49, 95% CI 39.37-89.90). Seroresponse rates were higher following laser + Viaskin-PT 25 μg (4/5 (80.0%), 95% CI 28.4-99.5) and 50 μg (22/25 (88.0%), 95% CI 68.8-97.5) than laser + Viaskin-placebo (0/12 (0.0%), 95% CI 0.0-26.5).

CONCLUSIONS

Viaskin-PT applied after laser-based epidermal skin preparation showed encouraging safety and immunogenicity results: anti-PT booster responses were not inferior to those elicited by Boostrix®dTpa. This study is registered at ClinicalTrials.gov (NCT03035370) and was funded by DBV Technologies.

Influenza and pertussis vaccination during pregnancy - attitudes, practices and barriers in gynaecological practices in Germany

Background

In Germany, antenatal influenza vaccination is recommended since 2010, but uptake remains low. Several countries recently introduced antenatal pertussis vaccination, which is currently under consideration in Germany. We conducted a survey among gynaecologists on attitudes, practices and barriers regarding influenza and pertussis vaccination during pregnancy.

Methods

Gynaecologists were invited to complete a pre-tested, 24-item questionnaire published in the German Professional Association of Gynaecologists’ journal in September 2017 within 2 months. Associations between variables were examined using Chi-Squared, Fischer’s Exact or t-tests. Variables associated with gynaecologists’ self-reported implementation of vaccination in pregnant women were identified using univariate and multivariate logistic regression analyses.

Results

Of 867 participants (response 11%), 91.4 and 59.4% reported currently vaccinating pregnant women against influenza and pertussis, respectively. Gynaecologists who reported obtaining annual influenza vaccination and actively informing their patients about these vaccinations were significantly more likely to vaccinate pregnant women against influenza (96.5% vs. 65.7 and 95.1% vs. 62.2%) and pertussis (63.1% vs. 44.3 and 82.4% vs. 12.9%). Performing influenza vaccination was least likely among gynaecologists who perceived logistical difficulties as a vaccination barrier (35.9%), while pertussis vaccination was least likely if the lacking official recommendation (32.0%), logistical difficulties (27.1%), safety concerns (17.5%) and limited vaccine effectiveness (11.1%) were perceived as barriers. Of participants not yet vaccinating pregnant women against pertussis, 86.5% reported they would follow an official recommendation. Including vaccination recommendations in the maternity record (95.2%) and informing the public (88.7%) and health care professionals (86.6%) were considered the most suitable measures to achieve high pertussis vaccination coverage.

Conclusions

The large proportion reporting performance of influenza vaccination during pregnancy and high acceptance of a potential recommendation for pertussis vaccination reflected positive attitudes towards vaccination among participants. However, factors associated with failure to vaccinate may be more prevalent among non-participants. Results suggest that gynaecologists’ confidence in vaccination is crucial for implementing vaccination in pregnancy. Thus, doubts on vaccine effectiveness and safety should be allayed among gynaecologists and pregnant women via various communication channels, and solutions for logistical barriers sought. Including antenatal vaccination recommendations in the maternity record would serve as an important reminder for both groups.

Electronic supplementary material

The online version of this article (10.1186/s12913-019-4437-y) contains supplementary material, which is available to authorized users.

Assays for Determining Pertussis Toxin Activity in Acellular Pertussis Vaccines

Whooping cough is caused by the bacterium Bordetella pertussis. There are currently two types of vaccines that can prevent the disease; whole cell vaccines (WCV) and acellular vaccines (ACV). The main virulence factor produced by the organism is pertussis toxin (PTx). This toxin is responsible for many physiological effects on the host, but it is also immunogenic and in its detoxified form is the main component of all ACVs. In producing toxoid for vaccines, it is vital to achieve a balance between sufficiently detoxifying PTx to render it safe while maintaining enough molecular structure that it retains its protective immunogenicity. To ensure that the first part of this balancing act has been successfully achieved, assays are required to accurately measure residual PTx activity in ACV products accurately. Quality control assays are also required to ensure that the detoxification procedures are robust and stable. This manuscript reviews the methods that have been used to achieve this aim, or may have the potential to replace them, and highlights their continuing requirement as vaccines that induce a longer lasting immunity are developed to prevent the re-occurrence of outbreaks that have been observed recently.

New Pertussis Vaccines: A Need and a Challenge

Effective diphtheria, tetanus toxoids, whole-cell pertussis (wP) vaccines were used for massive immunization in the 1950s. The broad use of these vaccines significantly reduced the morbidity and mortality associated with pertussis. Because of reports on the induction of adverse reactions, less-reactogenic acellular vaccines (aP) were later developed and in many countries, especially the industrialized ones, the use of wP was changed to aP. For many years, the situation of pertussis seemed to be controlled with the use of these vaccines, however in the last decades the number of pertussis cases increased in several countries. The loss of the immunity conferred by the vaccines, which is faster in the individuals vaccinated with the acellular vaccines, and the evolution of the pathogen towards geno/phenotypes that escape more easily the immunity conferred by the vaccines were proposed as the main causes of the disease resurgence. According to their composition of few immunogens, the aP vaccines seem to be exerting a greater selection pressure on the circulating bacterial population causing the prevalence of bacterial isolates defective in the expression of vaccine antigens. Under this context, it is clear that new vaccines against pertussis should be developed. Several vaccine candidates are in preclinical development and few others have recently completed phaseI/phaseII trials. Vaccine candidate based on OMVs is a promising candidate since appeared overcoming the major weaknesses of current aP-vaccines. The most advanced development is the live attenuated-vaccine BPZE1 which has successfully completed a first-in-man clinical trial.