Antibody responses to Bordetella pertussis Fim2 or Fim3 following immunization with a whole-cell, two-component, or five-component acellular pertussis vaccine and following pertussis disease in children in Sweden in 1997 and 2007

Biological differences between FIM2 and FIM3 fimbriae of Bordetella pertussis: not just the serotype

INTRODUCTION

Bordetella pertussis still circulates worldwide despite vaccination. Fimbriae are components of some acellular pertussis vaccines. Population fluctuations of B. pertussis fimbrial serotypes (FIM2 and FIM3) are observed, and fim3 alleles (fim3-1 [clade 1] and fim3-2 [clade 2]) mark a major phylogenetic subdivision of B. pertussis.

OBJECTIVES

To compare microbiological characteristics and expressed protein profiles between fimbrial serotypes FIM2 and FIM3 and genomic clades.

METHODS

A total of 19 isolates were selected. Absolute protein abundance of the main virulence factors, autoagglutination and biofilm formation, bacterial survival in whole blood, induced blood cell cytokine secretion, and global proteome profiles were assessed.

RESULTS

Compared to FIM3, FIM2 isolates produced more fimbriae, less cellular pertussis toxin subunit 1 and more biofilm, but auto-agglutinated less. FIM2 isolates had a lower survival rate in cord blood, but induced higher levels of IL-4, IL-8 and IL-1β secretion. Global proteome comparisons uncovered 15 differentially produced proteins between FIM2 and FIM3 isolates, involved in adhesion and metabolism of metals. FIM3 isolates of clade 2 produced more FIM3 and more biofilm compared to clade 1.

CONCLUSION

FIM serotype and fim3 clades are associated with proteomic and other biological differences, which may have implications on pathogenesis and epidemiological emergence.

Global spatial dynamics and vaccine-induced fitness changes of Bordetella pertussis

As with other pathogens, competitive interactions between Bordetella pertussis strains drive infection risk. Vaccines are thought to perturb strain diversity through shifts in immune pressures; however, this has rarely been measured because of inadequate data and analytical tools. We used 3344 sequences from 23 countries to show that, on average, there are 28.1 transmission chains circulating within a subnational region, with the number of chains strongly associated with host population size. It took 5 to 10 years for B. pertussis to be homogeneously distributed throughout Europe, with the same time frame required for the United States. Increased fitness of pertactin-deficient strains after implementation of acellular vaccines, but reduced fitness otherwise, can explain long-term genotype dynamics. These findings highlight the role of vaccine policy in shifting local diversity of a pathogen that is responsible for 160,000 deaths annually.

Whole-cell pertussis vaccine in early infancy for the prevention of allergy in children

BACKGROUND

Atopic diseases are the most common chronic conditions of childhood. The apparent rise in food anaphylaxis in young children over the past three decades is of particular concern, owing to the lack of proven prevention strategies other than the timely introduction of peanut and egg. Due to reported in vitro differences in the immune response of young infants primed with whole-cell pertussis (wP) versus acellular pertussis (aP) vaccine, we systematically appraised and synthesised evidence on the safety and the potential allergy preventive benefits of wP, to inform recommendation for future practice and research.

OBJECTIVES

To assess the efficacy and safety of wP vaccinations in comparison to aP vaccinations in early infancy for the prevention of atopic diseases in children.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials, Ovid MEDLINE, Embase, and grey literature. The date of the search was 7 September 2020.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and non-randomised studies of interventions (NRSIs) that reported the occurrence of atopic diseases, and RCTs only to assess safety outcomes. To be included studies had to have at least six months follow-up, and involve children under 18 years old, who received a first dose of either wP (experimental intervention) or aP (comparator) before six months of age.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened studies for eligibility, extracted the data, and assessed risk of bias using standard Cochrane methods. We assessed the certainty of the evidence using GRADE. Our primary outcomes were diagnosis of IgE-mediated food allergy and all-cause serious adverse events (SAEs). Secondary outcomes included: diagnosis of not vaccine-associated anaphylaxis or urticaria, diagnosis of asthma, diagnosis of allergic rhinitis, diagnosis of atopic dermatitis and diagnosis of encephalopathy. Due to paucity of RCTs reporting on the atopic outcomes of interest, we assessed a broader outcome domain (cumulative incidence of atopic disease) as specified in our protocol. We summarised effect estimates as risk ratios (RR) and 95% confidence intervals (CI). Where appropriate, we pooled safety data in meta-analyses using fixed-effect Mantel-Haenszel methods, without zero-cell corrections for dichotomous outcomes.

MAIN RESULTS

We identified four eligible studies reporting on atopic outcomes, representing 7333 children. Based on a single trial, there was uncertain evidence on whether wP vaccines affected the risk of overall atopic disease (RR 0.85, 95% CI 0.62 to 1.17) or asthma only (RR 1.04, 95% CI 0.59 to 1.82; 497 children) by 2.5 years old.Three NRSIs were judged to be at serious or critical risk of bias due to confounding, missing data, or both, and were ineligible for inclusion in a narrative synthesis.  We identified 21 eligible studies (137,281 children) that reported the safety outcomes of interest. We judged seven studies to be at high risk of bias and those remaining, at unclear risk.  The pooled RR was 0.94 for all-cause SAEs (95% CI 0.78 to 1.15; I² = 0%; 15 studies, 38,072 children). For every 1000 children primed with a first dose of wP, 11 had an SAE. The corresponding risk with aP was 12 children (95% CI 9 to 13). The 95% CI around the risk difference ranged from three fewer to two more events per 1000 children, and the certainty of the evidence was judged as moderate (downgraded one level for imprecision). No diagnoses of encephalopathy following vaccination were reported (95% CI around the risk difference - 5 to 12 per 100,000 children; seven primary series studies; 115,271 children). The certainty of the evidence was judged as low, since this is a serious condition, and we could not exclude a clinically meaningful difference.

AUTHORS' CONCLUSIONS

There is very low-certainty evidence that a first dose of wP given early in infancy, compared to a first dose of aP, affects the risk of atopic diseases in children. The incidence of all-cause SAEs in wP and aP vaccinees was low, and no cases of encephalopathy were reported. The certainty of the evidence was judged as moderate for all-cause SAEs, and low for encephalopathy. Future studies should use sensitive and specific endpoints of clinical relevance, and should be conducted in settings with high prevalence of IgE-mediated food allergy. Safety endpoints should prioritise common vaccine reactions, parental acceptability, SAEs and their potential relatedness to the dose administered.

Acellular Pertussis Vaccine Components: Today and Tomorrow

Pertussis is a highly communicable acute respiratory infection caused by Bordetella pertussis. Immunity is not lifelong after natural infection or vaccination. Pertussis outbreaks occur cyclically worldwide and effective vaccination strategies are needed to control disease. Whole-cell pertussis (wP) vaccines became available in the 1940s but have been replaced in many countries with acellular pertussis (aP) vaccines. This review summarizes disease epidemiology before and after the introduction of wP and aP vaccines, discusses the rationale and clinical implications for antigen inclusion in aP vaccines, and provides an overview of novel vaccine strategies aimed at better combating pertussis in the future.

DTaP5-HBV-IPV-Hib pediatric hexavalent combination vaccine for use in children from 6 weeks through to 4 years of age

Introduction: Combination vaccines reduce the number of injections received by children, hence improving timeliness and coverage, and general acceptability among caregivers and health-care providers. The most recent hexavalent vaccine, DTaP5-HBV-IPV-Hib, has been also approved by the FDA.Areas covered: DTaP5-HBV-IPV-Hib has demonstrated good immunogenic and safety profiles, not inferior to other hexavalent vaccines already in use in the European market. Either (2p+1/3p+1) immunization schedules can be used with no significant differences. A low incidence of severe adverse events has been shown, similar to other combination vaccines. No issues have arisen when concomitantly administered with other vaccines.Expert opinion: The inclusion of two additional acellular pertussis components (FIM2 and FIM3) might yield better protection against the disease, but this remains to be clinically proven. The new vaccine uses Hib with unique protein carrier (PRP-OMPC) which elicits higher earlier immune response without compromising safety. Compliance with the immunization schedules is expected to increase by decreasing the number of injections needed in combined vaccines for a single visit. In addition, the improvements on the ease-of-use by its liquid-formulation, makes the vaccine preparation more acceptable for use in clinics and may reduce the odds of administration errors.

The evolving nature of Bordetella pertussis in Ontario, Canada, 2009-2017: strains with shifting genotypes and pertactin deficiency

This study examined the evolving nature of Bordetella pertussis in Ontario, Canada, by characterizing isolates for their genotypes and expression of pertactin (PRN). From 2009 to 2017, 413 B. pertussis were cultured from pertussis cases at the Public Health Ontario Laboratory. Their genotypes were determined by partial gene sequence analysis of their virulence and (or) vaccine antigens: filamentous haemagglutinin, PRN, fimbriae 3, and pertussis toxin, including the promoter region. Expression of PRN was measured by Western immunoblot. Two predominant genotypes, ST-1 and ST-2, were found throughout the study and were responsible for 47.5% and 46.3% of all case isolates, respectively. The prevalence of ST-1 appeared to fluctuate from 80.3% in 2009 to 20.0% in 2014 and 58.5% in 2017, while the prevalence of ST-2 changed from 18.4% in 2009 to 80.0% in 2014 and 26.2% in 2017. A PRN-deficient strain was first noted in 2011 (16.7%), and its prevalence increased to 70.8% in 2016 but decreased to 46.2% in 2017. More ST-2 (46.6%) than ST-1 (16.8%) strains were associated with PRN deficiency. Newer ST-21 and ST-22 found in 2015-2017 were uniformly PRN deficient. The impact of the evolving nature of B. pertussis on disease epidemiology requires further longitudinal studies.

Pertussis Prevention: Reasons for Resurgence, and Differences in the Current Acellular Pertussis Vaccines

Pertussis is an acute respiratory disease caused by Bordetella pertussis. Due to its frequency and severity, prevention of pertussis has been considered an important public health issue for many years. The development of the whole-cell pertussis vaccine (wPV) and its introduction into the pediatric immunization schedule was associated with a marked reduction in pertussis cases in the vaccinated cohort. However, due to the frequency of local and systemic adverse events after immunization with wPV, work on a less reactive vaccine was undertaken based on isolated B. pertussis components that induced protective immune responses with fewer local and systemic reactions. These component vaccines were termed acellular vaccines and contained one or more pertussis antigens, including pertussis toxin (PT), filamentous haemagglutinin (FHA), pertactin (PRN), and fimbrial proteins 2 (FIM2) and 3 (FIM3). Preparations containing up to five components were developed, and several efficacy trials clearly demonstrated that the aPVs were able to confer comparable short-term protection than the most effective wPVs with fewer local and systemic reactions. There has been a resurgence of pertussis observed in recent years. This paper reports the results of a Consensus Conference organized by the World Association for Infectious Disease and Immunological Disorders (WAidid) on June 22, 2018, in Perugia, Italy, with the goal of evaluating the most important reasons for the pertussis resurgence and the role of different aPVs in this resurgence.

Vaccine acquired pertussis immunity was weakened at 4 years of age and asymptomatic pertussis infection was suspected based on serological surveillance

Serological surveillance of pertussis antibodies was performed in 118 children aged 1-12 years. The positivity of pertussis toxin (PT) antibodies was low at 4-6 years and significantly higher at 8-9 years, compared with those at 6 years. Fimbriae 2 (Fim2) antibody showed similar response to the PT antibody. Higher antibody titers against Fim3 were observed among subjects ≥5 years and highest at 8 years. Data demonstrated that the vaccine-induced antibodies decayed by 4-5 years and subclinical pertussis infection was suspected thereafter, suggesting the need for additional dose at around 4-5 years.

Highly differentiated human airway epithelial cells: a model to study host cell-parasite interactions in pertussis

BACKGROUND

Bordetella pertussis colonizes the human respiratory mucosa. Most studies on B. pertussis adherence have relied on cultured mammalian cells that lack key features present in differentiated human airway cells or on animal models that are not natural hosts of B. pertussis. The objectives of this work were to evaluate B. pertussis infection in highly differentiated human airway cells in vitro and to show the role of B. pertussis fimbriae in cell adherence.

METHODS

Primary human airway epithelial (PHAE) cells from human bronchi and a human bronchial epithelial (HBE) cell line were grown in vitro under air-liquid interface conditions.

RESULTS

PHAE and HBE cells infected with B. pertussis wild-type strain revealed bacterial adherence to the apical surface of cells, bacteria-induced cytoskeleton changes, and cell detachment. Mutations in the major fimbrial subunits Fim2/3 or in the minor fimbrial adhesin subunit FimD affected B. pertussis adherence to predominantly HBE cells. This cell model recapitulates the morphologic features of the human airway infected by B. pertussis and confirms the role of fimbriae in B. pertussis adherence. Furthermore, HBE cells show that fimbrial subunits, and specifically FimD adhesin, are critical in B. pertussis adherence to airway cells.

CONCLUSIONS

The relevance of this model to study host-parasite interaction in pertussis lies in the striking physiologic and morphologic similarity between the PHAE and HBE cells and the human airway ciliated and goblet cells in vivo. These cells can proliferate in vitro, differentiate, and express the same genetic profile as human respiratory cells in vivo.

Plasticity of fimbrial genotype and serotype within populations of Bordetella pertussis: analysis by paired flow cytometry and genome sequencing

The fimbriae of Bordetella pertussis are required for colonization of the human respiratory tract. Two serologically distinct fimbrial subunits, Fim2 and Fim3, considered important vaccine components for many years, are included in the Sanofi Pasteur 5-component acellular pertussis vaccine, and the World Health Organization recommends the inclusion of strains expressing both fimbrial serotypes in whole-cell pertussis vaccines. Each of the fimbrial major subunit genes, fim2, fim3, and fimX, has a promoter poly(C) tract upstream of its −10 box. Such monotonic DNA elements are susceptible to changes in length via slipped-strand mispairing in vitro and in vivo, which potentially causes on/off switching of genes at every cell division. Here, we have described intra-culture variability in poly(C) tract lengths and the resulting fimbrial phenotypes in 22 recent UK B. pertussis isolates. Owing to the highly plastic nature of fimbrial promoters, we used the same cultures for both genome sequencing and flow cytometry. Individual cultures of B. pertussis contained multiple fimbrial serotypes and multiple different fimbrial promoter poly(C) tract lengths, which supports earlier serological evidence that B. pertussis expresses both serotypes during infection.

Bordetella pertussis fimbriae (Fim): relevance for vaccines

Bordetella pertussis produces two serologically distinct fimbriae, Fim2 and Fim3. Expression of these antigens is governed by the BvgA/S system and by the length of a poly(C) tract in the promoter of each gene. Fim2 and Fim3 are important antigens for whole cell pertussis vaccines as clinical trials have shown an association of anti-fimbriae antibody-mediated agglutination and protection. The current five component acellular pertussis vaccine contains co-purified Fim2/3 and provided good efficacy in clinical trials with the anti-Fim antibody response correlating with protection when pre and post exposure antibody levels were analysed. The predominant serotype of B. pertussis isolates has changed over time in most countries but it is not understood whether this is vaccine-driven or whether serotype is linked to the prevailing predominant genotype. Recent studies have shown that both Fim2 and Fim3 are expressed during infection and that Fim2 is more immunogenic than Fim3 in the acellular vaccine.

Improved pertussis vaccines based on adjuvants that induce cell-mediated immunity

Bordetella pertussis is a Gram-negative bacterium that causes the severe and sometimes lethal respiratory disease whooping cough in infants and children. There has been a recent resurgence in the number of cases of pertussis in several countries with high vaccine coverage. This has been linked with waning or ineffective immunity induced by current acellular pertussis vaccines. These acellular pertussis vaccines are formulated with alum as the adjuvant, which promotes strong antibody responses but is less effective at inducing Th1-type responses crucial for effective bacterial clearance. Studies in animal models have demonstrated that replacing alum with alternative adjuvants, such as toll-like receptor agonists, can promote more robust cell-mediated immunity and confer a high level of protection against infection following respiratory challenge.