Clinical and immunological risk factors associated with Haemophilus influenzae type b conjugate vaccine failure in childhood

Haemophilus influenzae Type b Vaccine Failure in Portugal: A Nationwide Multicenter Pediatric Survey

BACKGROUND

Despite the high effectiveness of the Haemophilus influenzae type b (Hib) vaccine in preventing invasive disease (ID) in children, Hib vaccine failures (VFs) cases may still occur. This study aimed to characterize the Hib-VF cases in Portugal in a 12-year period and trying to identify the possible associated risk factors.

METHODS

Prospective descriptive nationwide surveillance study. Bacteriologic and molecular studies were performed at the same Reference Laboratory. Clinical data were collected by the referring pediatrician.

RESULTS

Hib was identified in 41 children with ID and 26 (63%) were considered VF. Nineteen (73%) cases occurred in children less than 5 years old; 12 (46%) occurred before the Hib vaccine booster dose at 18 months of age. Comparing the first and the last 6-year periods of the study, the incidence rate of Hib, VF and total H. influenzae (Hi) ID significantly raised ( P < 0.05). VF cases corresponded, respectively, to 13.5% (7/52) and 22% (19/88) of total Hi-ID cases ( P = 0.232). Two children died due to epiglottitis and 1 acquired sensorineural hearing loss. Only 1 child had an inborn error of immunity. The immunologic workup performed in 9 children revealed no significant abnormalities. All 25 Hib-VF strains analyzed belonged to the same clonal complex 6.

CONCLUSIONS

In Portugal, more than 95% of children are vaccinated against Hib, but severe Hib-ID cases still occur. No predisposing factors were clearly identified to justify the increased number of VF in recent years. Along with continued Hi-ID surveillance, Hib colonization and serologic studies should be implemented.

The effect of human vaccination behaviour on strain competition in an infectious disease: An imitation dynamic approach

Strain competition plays an important role in shaping the dynamics of multiple pathogen outbreaks in a population. Competition may lead to exclusion of some pathogens, while it may influence the invasion of an emerging mutant in the population. However, little emphasis has been given to understand the influence of human vaccination choice on pathogen competition or strain invasion for vaccine-preventable infectious diseases. Coupling game dynamic framework of vaccination choice and compartmental disease transmission model of two strains, we explore invasion and persistence of a mutant in the population despite having a lower reproduction rate than the resident one. We illustrate that higher perceived strain severity and lower perceived vaccine efficacy are necessary conditions for the persistence of a mutant strain. The numerical simulation also extends these invasion and persistence analyses under asymmetric cross-protective immunity of these strains. We show that the dynamics of this cross-immunity model under human vaccination choices is determined by the interplay of parameters defining the cross-immune response function, perceived risk of infection, and vaccine efficacy, and it can exhibit invasion and persistence of mutant strain, even complete exclusion of resident strain in the regime of sufficiently high perceived risk. We conclude by discussing public health implications of the results, that proper risk communication in public about the severity of the disease is an important task to reduce the chance of mutant invasion. Thus, understanding pathogen competitions under social interactions and choices may be an important component for policymakers for strategic decision-making.

Invasive Haemophilus influenzae type b infection in a patient with transient hypogammaglobulinemia of infancy

We describe a patient with invasive Haemophilus influenzae type b (Hib) infection despite being completely immunized by a conjugate Hib vaccine. Although Hib vaccination has contributed to significant reduction in invasive Hib infection, there are some case reports of invasive Hib infections despite immunization. Immunoglobulin (Ig) deficiency is the main cause of primary vaccine failure, and IgG2 subclass deficiency is known to be the leading cause. A previously healthy 13-month-old boy visited the outpatient clinic with a 5-day history of fever (40.0 °C), cough, and vomiting, and was diagnosed with bacterial meningitis, purulent pericarditis, and arthritis. Hib was recovered from blood, cerebrospinal fluid, and pericardial fluid. Immunological examination revealed subnormal IgG and IgA titers at 13 and 17 months of age. Serum IgG2 titer was recovered at 17 months of age despite being low at 13 months. Comprehensive gene analysis for primary immunodeficiency syndromes (primary antibody deficiency, common variable immunodeficiency, and toll-like receptor abnormalities) were negative. The antibody titer against Hib [anti-polyribosylribitol phosphate (PRP) antibody] was lower than the long-term protective titer (1.0 μg/ml) at 13 months of age, but was reactively increased to 2.38 μg/mL two months after booster immunization. Transient hypogammaglobulinemia of infancy (THI) is described as an accentuation and prolongation of the physiologic Ig nadir that is normally observed during infancy and defined as low IgG and IgA levels in the first three years of life. We speculate that he developed an invasive Hib infection as a result of primary Hib vaccine failure caused by THI.

Invasive Haemophilus influenzae type b (Hib) disease in children in Italy, after 20 years of routine use of conjugate Hib vaccines

Haemophilus influenzae serotype b (Hib) was the leading cause of bacterial meningitis in children before the implementation of infant immunization with conjugate Hib vaccines. Despite the effectiveness of the vaccine, invasive Hib disease cases (i.e. isolation of Hib from a normally sterile site) are still reported in children. All invasive Hib disease cases in children ≤ 15 years reported through the National Surveillance System of Invasive Bacterial Disease, during 2012-2018 in Italy, were analyzed. Hib PCR-confirmed isolates were subjected to MLST and PFGE analysis. The number of copies of the capb locus, a virulence factor potentially contributing to true vaccine failures (TVFs), was determined by Southern blot analysis. Vaccine effectiveness (VE) was determined using a multiple Poisson regression model. 31 cases of invasive Hib disease in children were reported. Fourteen children were vaccinated (TVFs), 14 were unvaccinated and 2 partially vaccinated (vaccination status was unknown for 1 case). The median age of children was 12 months (range 3 months-15 years). A decrease in vaccination coverage was observed in 2014-2016 (source Ministry of Health), and a rise in incidence was documented from 2016 until 2018, especially in children < 5 years. Vaccine effectiveness was estimated to be 83% (95% CI:45-95). 24 isolates were available. The predominant ST was ST6 (70.8%). Cluster analysis of ST6 isolates by PFGE identified five variants. Six isolates (25%) contained multiple copies of the capb locus distributed among TVFs (30%) and unvaccinated children (16.7%). Our data show that both failures to vaccinate and TVFs are associated with invasive Hib disease in children in Italy, during the vaccination era. Most cases in children ≤ 2 years were vaccine-preventable, since they occurred in unvaccinated subjects (13/21 cases, 62%). No host predisposing factors for TVF were recognized. TVFs were not significantly associated with either specific genotypes or amplification status of the capb locus.

Invasive Haemophilus influenzae Type b Disease in the Post Hexavalent Era: Ten Years of Molecular Surveillance in Tuscany

BACKGROUND

The epidemiologic characteristics of invasive Haemophilus influenzae type b disease (HIBD) have markedly changed since the introduction of the Haemophilus influenzae type b (Hib) conjugate vaccine worldwide. The immunization schedule against Haemophilus influenzae type b differs in Europe.

METHODS

This is a retrospective observational study which evaluates all the data included in the molecular surveillance register for invasive infectious diseases at the Laboratory of Molecular Diagnosis at Meyer Children's University Hospital from December 2008 to December 2018 with a diagnosis of invasive HIBD in children <5 years of age.

RESULTS

We identified 4 cases of HIBD: all the cases presented signs or symptoms of invasive infection and the H. influenzae type b was identified in cerebrospinal fluid, or blood or bronchoalveolar lavage by molecular test. The crude incidence for Hib invasive disease in Tuscany is 0.26/100,000 p-y in children younger than 5 years, significantly different from the incidence rate before the introduction of the Hib vaccination. Vaccination effectiveness can be estimated at 97.9% and the impact of hexavalent (2p+1) vaccine at 99.6%.

CONCLUSIONS

This work confirms the high impact of the hexavalent vaccine 2p+1 schedule for HIBD in children <5 years, emphasizing the role of molecular test for HIBD diagnosis and surveillance.

Haemophilus influenzae type b invasive infections in children hospitalized between 2000 and 2017 in a Pediatric Reference Hospital (PRH)

BACKGROUND

Uruguay incorporated the conjugate vaccine against Haemophilus influenzae b (Hib) in 1994. In 2008, the vaccine was changed from one with natural conjugated capsular polysaccharide to one with a synthetic polysaccharide component. We describe the frequency and characteristics of invasive Hib infections in children hospitalized in a Pediatric Reference Hospital (PRH) between January 1st, 2000 and December 31st, 2017.

METHODS

Sterile site Hib isolations from hospitalized children were included. Clinical and microbiological characteristics were analyzed. Favorable conditions for the infection were considered: incomplete immunization, immunodeficiencies and associated pathologies. Two periods are described: 1, prior to vaccine change (1/1 st/2000- 12/31/08) and 2, post-change (1/1 st/09- 12/31st/17).

RESULTS

45 children were hospitalized: 5 in the first period and 40 in the second. The hospitalization rate per 10,000 discharges was 0.41 (95% CI 0.05-0.77) and 4.2/10,000 (95% CI 2.89-5.48), respectively (p < 0.01). The diagnoses at discharge were: meningitis/ventriculitis (20), pneumonia (16), bacteremia (3), epiglottitis (1), arthritis (1), cellulitis (3) and obstruction of the upper airway (1). Four children presented comorbidities. Twenty seven received less than 3 doses of anti-Hib vaccination and 18 were properly vaccinated (2 were immunodeficient). The median hospitalization was 14 days, 18 children required intensive therapy.

CONCLUSIONS

Observed change may be due to: incomplete primary series, inhomogeneous vaccine coverage and immunogenicity of the synthetic polysaccharide. To reduce this public health problem, epidemiological surveillance.

Characteristics and Serotype Distribution of Childhood Cases of Invasive Pneumococcal Disease Following Pneumococcal Conjugate Vaccination in England and Wales, 2006-2014

Background

The 7-valent and 13-valent pneumococcal conjugate vaccines (PCV7 and PCV13, respectively) are highly effective in preventing invasive pneumococcal disease (IPD) caused by vaccine serotypes. Vaccine failure (vaccine-type IPD after age-appropriate immunization) is rare. Little is known about the risk, clinical characteristics, or outcomes of PCV13 compared to PCV7 vaccine failure.

Methods

Public Health England conducts IPD surveillance and provides a national reference service for serotyping pneumococcal isolates in England and Wales. We compared the epidemiology, rates, risk factors, serotype distribution, clinical characteristics, and outcomes of IPD in children with PCV13 and PCV7 vaccine failure.

Results

A total of 163 episodes of PCV failure were confirmed in 161 children over 8 years (4 September 2006 to 3 September 2014) in 10 birth cohorts. After 3 vaccine doses, PCV7 and PCV13 failure rates were 0.19/100000 (95% confidence interval [CI], .10-.33 [57 cases]) and 0.66/100000 (95% CI, .44-.95 [104 cases]) vaccinated person-years, respectively. Children with PCV13 failure were more likely to be healthy (87/105 [82.9%] vs 37/56 [66.1%]; P = .02), present with bacteremic lower respiratory tract infection (LRTI) (61/105 [58.1%] vs 11/56 [19.6%]; P < .001), and develop empyema (41/61 [67.2%] vs 1/11 [9.1%]; P < .001) compared to PCV7 failures. Serotypes 3 (n = 38 [36.2%]) and 19A (n = 30 [28.6%]) were responsible for most PCV13 failures. Six children died (4% [95% CI, 1%-8%]), including 5 with comorbidities.

Conclusions

PCV failure is rare and, compared to PCV7 serotypes, the additional PCV13 serotypes are more likely to cause bacteremic LRTI and empyema in healthy vaccinated children.

Clinical Characterization of Invasive Disease Caused by Haemophilus influenzae Serotype b in a High Vaccination Coverage Setting

This national study characterized invasive Haemophilus influenzae serotype b infections. Vaccinated (n = 41) and nonvaccinated (n = 10) cases were similar regarding presentation as meningitis (68.8% vs 90.0%; P = .25), predisposing factors (29.3% vs 20.0%; P = .76), admission to intensive care unit or death (22.0% vs 10.0%; P = 1.00), or sequelae (21.6% vs 10.0%; P = .81). Haemophilus influenzae serotype b occurred in vaccinated, healthy children with comparable disease course.

Acute Infections That Produce Upper Airway Obstruction

This chapter discusses the common and potentially serious infective causes of acute upper airway obstruction in children. The laryngeal anatomy of young children makes them particularly susceptible to upper airway obstruction, and during acute infections this is exacerbated by inflammation and edema of the airway mucosa. The most common cause of infective upper airway obstruction in children is viral laryngotracheobronchitis, or croup, which is usually a mild and self-limiting illness, but management with corticosteroids may still be necessary. Bacterial causes of upper airway obstruction have fortunately become rare since the introduction of the Haemophilus influenzae B (HiB) immunization, but a few cases of epiglottitis do still occur due to nonimmunization, vaccine failure, and infection with non-HiB organisms. These cases constitute a medical emergency due to the risk of rapid progression to complete airway obstruction. Other rare conditions are discussed including bacterial tracheitis, diphtheria, retropharyngeal, and peritonsillar abscesses. Key learning points in this chapter include the main discriminating factors of the various causes of infective upper airway obstruction, the importance of a calm and minimally distressing approach to the child presenting with stridor, and the need for early anesthetic team involvement in cases with a suspected bacterial etiology or signs of impending airway obstruction.

Increasing trend in invasive non-typeable Haemophilus influenzae disease and molecular characterization of the isolates, Italy, 2012-2016

Routine immunization of infants with conjugate vaccines against Haemophilus influenzae type b (Hib) has greatly reduced the incidence of invasive Hib disease; however changes in the epidemiology of H. influenzae disease have occurred. We describe the epidemiology of invasive H. influenzae disease and the characterization of isolates collected in Italy between 2012 and 2016. Trends in the overall incidence of invasive H. influenzae disease were calculated. Isolates were characterized by PCR capsular genotyping, antimicrobial susceptibility testing, ampicillin resistance-associated gene sequencing and MLST. Trends in incidence by serotype and serotype-specific distribution were estimated using multiple imputation of missing data. The overall incidence of invasive H. influenzae disease increased 22.5% yearly (from 0.11/100,000 in 2012 to 0.24/100,000 in 2016). Most cases (82.0%) were due to non-typeable H. influenzae (NTHi). An increasing trend in NTHi disease burden was estimated; the highest rise was among infants <12 months (40.8% annual increase). Invasive Hib disease showed a fluctuating trend with a clear increase in 2016, while we found an increasing trend for disease due to non-Hib capsulated serotypes in the elderly (32.9% annual increase). Ampicillin resistance mediated by either β-lactamase or altered penicillin-binding proteins 3 (PBP3) increased. In spite of genetic diversity of NTHi, sequence types (STs) associated with ampicillin resistance status were identified (ST103/ST106 linked to β-lactamase production and ST14 linked to a specific PBP3 substitution pattern). The increasing trend in invasive NTHi disease in infants is of concern underlying the need for the development of a future vaccine against NTHi.

Conjugate Haemophilus influenzae type b vaccines for sickle cell disease

BACKGROUND

People affected with sickle cell disease (SCD) are at high risk of infection from Haemophilus influenzae type b (Hib). Before the implementation of Haemophilus influenzae type b conjugate vaccination in high-income countries, this was responsible for a high mortality rate in children under five years of age. In African countries, where coverage of this vaccination is still extremely low, Hib remains one of the most common causes of bacteraemias in children with SCD. The increased uptake of this conjugate vaccination may substantially improve the survival of children with SCD. This is an update of a previously published Cochrane Review.

OBJECTIVES

The primary objective was to determine whether Hib conjugate vaccines reduce mortality and morbidity in children and adults with SCD.The secondary objectives were to assess the following in children and adults with SCD: the immunogenicity of Hib conjugate vaccines; the safety of these vaccines; and any variation in effect according to type of vaccine, mode of administration (separately or in combination with other vaccines), number of doses, and age at first dose.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched trial registries (04 July 2018) and contacted relevant pharmaceutical companies to identify unpublished trials.Date of last search of the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinoapthies Trials Register: 18 December 2017.

SELECTION CRITERIA

All randomised controlled trials (RCTs) and quasi-RCTs comparing Hib conjugate vaccines with placebo or no treatment, or comparing different types of Hib conjugate vaccines in people with SCD.

DATA COLLECTION AND ANALYSIS

No trials of Hib conjugate vaccines in people with SCD were found.

MAIN RESULTS

There is an absence of evidence from RCTs relating to the subject of this review.

AUTHORS' CONCLUSIONS

There has been a dramatic decrease in the incidence of invasive Hib infections observed in the post-vaccination era in people with SCD living in high-income countries. Therefore, despite the absence of evidence from RCTs, it is expected that Hib conjugate vaccines may be useful in children affected with SCD, especially in African countries where there is a high prevalence of the disease. The implementation of childhood immunisation schedules, including universal Hib conjugate vaccination, may substantially improve the survival of children with SCD living in low-income countries. We currently lack data to evaluate the potential effect of Hib vaccination among unvaccinated adults with SCD. Further research should assess the optimal Hib immunisation schedule in children and adults with SCD.

Common Queries About Immunizations in Preterm Infants

Preterm infants are at an increased risk of morbidity and mortality from vaccine-preventable diseases. Despite this, delays in routine immunization of preterm infants are common. Available guidelines clearly state that they should be immunized according to chronological age, irrespective of gestational age and birth weight or current weight. In this article, we try to assuage parental and provider doubts by reviewing data about immunogenicity, safety, and responses to routine immunizations in preterm infants with and without comorbidities. We also look at evidence for other strategies to help protect this fragile population. [Pediatr Ann. 2018;47(4):e147-e153.].

Risk factors for community-acquired bacterial meningitis

BACKGROUND

Bacterial meningitis is a significant burden of disease and mortality in all age groups worldwide despite the development of effective conjugated vaccines. The pathogenesis of bacterial meningitis is based on complex and incompletely understood host-pathogen interactions. Some of these are pathogen-specific, while some are shared between different bacteria.

METHODS

We searched the database PubMed to identify host risk factors for bacterial meningitis caused by the pathogens Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae type b, because they are three most common causative bacteria beyond the neonatal period.

RESULTS

We describe a number of risk factors; including socioeconomic factors, age, genetic variation of the host and underlying medical conditions associated with increased susceptibility to invasive bacterial infections in both children and adults.

CONCLUSIONS

As conjugated vaccines are available for these infections, it is of utmost importance to identify high risk patients to be able to prevent invasive disease.

Pneumococcal conjugate vaccine failure in children: A systematic review of the literature

BACKGROUND

Pneumococcal conjugate vaccines (PCVs) are highly effective in preventing pneumococcal invasive disease (IPD) due to serotypes included in the vaccines. The risk of vaccine-type IPD in immunised children (i.e. vaccine failure) has not been systematically assessed in countries with established PCV programmes.

METHODS

We undertook a systematic review of the English literature published from January 2000 to April 2016 to evaluate the vaccine schedule, risk factors, serotype distribution, clinical presentation and outcomes of vaccine failure in children vaccinated with the 7-valent (PCV7), 10-valent (PCV10), and 13-valent (PCV13) vaccines. Data sources included MEDLINE, EMBASE, Cochrane library, and references within identified articles.

RESULTS

We identified 1742 potential studies and included 20 publications involving 7584 participants in children aged ⩽5year-olds: 5202 received 2 doses followed by a booster in 10 studies, (68.6%), 64 (0.8%) received 3 doses without a booster in 2 studies, and 2318 received a 3+1 schedule (30.6%) in 8 studies. A total of 159 vaccine failure cases were identified, representing 2.1% [95% CI: 1.8-2.4%] of the reported IPD cases. Most studies did not report clinical characteristics or outcomes. Among eight studies reporting comorbidities, 33/77 patients (42.9%) had an underlying condition. The main serotypes associated with vaccine failure were 19F (51/128 cases with known serotype; 39.8%), 6B (33/128; 25.8%), and 4 (10/128; 7.8%). Only five studies reported patient outcomes, with a crude case fatality rate of 2.4% (2/85; 95%CI: 0.3-8.5%).

CONCLUSION

Pneumococcal conjugate vaccines have been implemented in national immunisation programmes for more than a decade, yet there are only a few studies reporting vaccine failure. PCV failure is rare, irrespective of vaccine or schedule. Co-morbidity prevalence was high amongst vaccine failure cases but case fatality rate was relatively low. There is a need for more systematic reporting vaccine failure cases in countries with established pneumococcal vaccination programmes.

Immunization of preterm infants

Vaccinations of premature infants are often delayed despite being at an increased risk of contracting vaccine preventable diseases. This article reviews the current knowledge on the immune response to widely used vaccines, on the protection derived from routine immunization and on vaccine safety and tolerability in a population of preterm infants. Available data evaluating the immune response of preterm infants support early immunization without correction for gestational age. For a number of antigens, the antibody response to initial doses of vaccines may be lower than that of term infants, but protective concentrations are often achieved and memory successfully induced. Vaccines are immunogenic, safe and well tolerated in preterm infants. Preterm infants should be vaccinated using the same schedules as those usually recommended for full-term infants, with the exception of the hepatitis B vaccine, where additional doses should be administered in infants receiving the first dose during the first days of life if they weighed less than 2000 g because of a documented reduced immune response.

Haemophilus influenzae type b meningitis in a vaccinated and immunocompetent child

Invasive Haemophilus influenzae type b (Hib) disease decreased dramatically after the introduction of conjugate vaccine in routine immunization schedules. We report a case of a fifteen-months-old girl, previously healthy and vaccinated, admitted in the emergency room with fever and vomiting. She was irritable and the Brudzinski's sign was positive. The cerebrospinal fluid (CSF) analysis showed pleocytosis and high protein level. Empiric intravenous antibiotics (ceftriaxone and vancomycin) were administered for suspected bacterial meningitis during 10 days. Serotyping of the Haemophilus influenzae strain found in CSF revealed a serotype b. After one year of follow-up no Hib meningitis sequelae were noted. Despite vaccination compliance and absence of risk factors, invasive Hib disease can occur due to vaccine failure. Efforts to keep the low incidence of invasive Hib disease should be directed to the maintenance of high vaccination coverage rates, combined with the notification and surveillance strategies already implemented in each country.

Children with Haemophilus influenzae type b (Hib) vaccine failure have long-term bactericidal antibodies against virulent Hib strains with multiple capsular loci

Children who develop invasive Haemophilus influenzae serotype b (Hib) disease after immunisation with a highly-effective conjugate vaccine are more likely to have been infected with Hib strains possessing multiple copies of the capsulation locus. Using a recently-validated serum bactericidal antibody (SBA) assay, we tested convalescent sera from 127 Hib vaccine failure cases against clinical Hib strains expressing 1-5 copies of the capsulation locus. SBA titres correlated weakly with anti-capsular IgG antibody concentrations and there was no association between SBA geometric mean titres and number of capsulation locus copies. After infection, children with Hib vaccine failure were equally protected against Hib strains with 1-5 copies of the capsulation locus.

Conjugate Haemophilus influenzae type b vaccines for sickle cell disease

BACKGROUND

People affected with sickle cell disease are at high risk of infection from Haemophilus influenzae type b. Before the implementation of Haemophilus influenzae type b conjugate vaccination in high-income countries, this was responsible for a high mortality rate in children under five years of age. In African countries, where coverage of this vaccination is still extremely low, Haemophilus influenzae type b remains one of the most common cause of bacteraemias in children with sickle cell disease. The increased uptake of this conjugate vaccination may substantially improve the survival of children with sickle cell disease.

OBJECTIVES

The primary objective was to determine whether Haemophilus influenzae type b conjugate vaccines reduce mortality and morbidity in children and adults with sickle cell disease.The secondary objectives were to assess the following in children and adults with sickle cell disease: the immunogenicity of Haemophilus influenzae type b conjugate vaccines; the safety of these vaccines; and any variation in effect according to type of vaccine, mode of administration (separately or in combination with other vaccines), number of doses, and age at first dose.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also contacted relevant pharmaceutical companies to identify unpublished trials.Date of last search: 23 November 2015.

SELECTION CRITERIA

All randomised and quasi-randomised controlled trials comparing Haemophilus influenzae type b conjugate vaccines with placebo or no treatment, or comparing different types of Haemophilus influenzae type b conjugate vaccines in people with sickle cell disease.

DATA COLLECTION AND ANALYSIS

No trials of Haemophilus influenzae type b conjugate vaccines in people with sickle cell disease were found.

MAIN RESULTS

There is an absence of evidence from randomised controlled trials relating to the subject of this review.

AUTHORS' CONCLUSIONS

There has been a dramatic decrease in the incidence of invasive Haemophilus influenzae type b infections observed in the post-vaccination era in people with sickle cell disease living in high-income countries. Therefore, despite the absence of evidence from randomised controlled trials, it is expected that Haemophilus influenzae type b conjugate vaccines may be useful in children affected with sickle cell disease, especially in African countries where there is a high prevalence of the disease. The implementation of childhood immunisation schedules, including universal Haemophilus influenzae type b conjugate vaccination, may substantially improve the survival of children with sickle cell disease living in low-income countries. We currently lack data to evaluate the potential effect of Haemophilus influenzae type b vaccination among unvaccinated adults with sickle cell disease. Further research should assess the optimal Hib immunisation schedule in children and adults with sickle cell disease.

Hib Vaccines: Past, Present, and Future Perspectives

Haemophilus influenzae type b (Hib) causes many severe diseases, including epiglottitis, pneumonia, sepsis, and meningitis. In developed countries, the annual incidence of meningitis caused by bacteria is approximately 5–10 cases per population of 100,000. The Hib conjugate vaccine is considered protective and safe. Adjuvants, molecules that can enhance and/or regulate the fundamental immunogenicity of an antigen, comprise a wide range of diverse compounds. While earlier developments of adjuvants created effective products, there is still a need to create new generations, rationally designed based on recent discoveries in immunology, mainly in innate immunity. Many factors may play a role in the immunogenicity of Hib conjugate vaccines, such as the polysaccharides and proteins carrier used in vaccine construction, as well as the method of conjugation. A Hib conjugate vaccine has been constructed via chemical synthesis of a Hib saccharide antigen. Two models of carbohydrate-protein conjugate have been established, the single ended model (terminal amination-single method) and cross-linked lattice matrix (dual amination method). Increased knowledge in the fields of immunology, molecular biology, glycobiology, glycoimmunology, and the biology of infectious microorganisms has led to a dramatic increase in vaccine efficacy.

Pediatric invasive Haemophilus influenzae infections in Israel in the era of Haemophilus influenzae type b vaccine: a nationwide prospective study

BACKGROUND

The conjugated Haemophilus influenzae (Hi) type b vaccine caused a marked decrease in invasive Hi disease rates. Nonencapsulated Hi infection now constitutes most invasive Hi morbidity and mortality. This study examines invasive Hi infection incidence in Israel in the postvaccine era years, 2003-2012, and characterizes the epidemiology, clinical diagnosis and case fatality rates of invasive Hi disease in children <15 years of age.

METHODS

An ongoing, nationwide prospective surveillance program for invasive Hi infections in Israel. Epidemiologic and clinical data were collected. Diagnoses were classified as meningitis, pneumonia, bacteremia/sepsis and other clinical foci.

RESULTS

Overall, 389 cases of invasive Hi infections were identified; 242 (62%) nontypable Hi (NTHi), 103 (26%) Hi type b (Hib) and 41 (11%) encapsulated non-b Hi (enbHi). Children <1 year of age accounted for 51% of the overall disease. Invasive Hi disease incidence in children <15 years of age was stable with a mean annual incidence (per 100,000) of 2.0 ± 0.4. The highest incidence of invasive Hi infections was among infants <1 year with rates of 6.2, 4.9, 1.6 and 12.7 for NTHi, Hib, enbHi and total Hi, respectively. The clinical diagnoses of NTHi and enbHi were similar, but differed from Hib with the former presenting mostly as isolated sepsis/bacteremia and the latter primarily as meningitis. Among children with invasive Hib infection, 40% were classified as vaccine failure.

CONCLUSIONS

In the post-Hib vaccination era, invasive Hi morbidity and mortality are largely attributed to NTHi sepsis. Still, with the changing epidemiology of invasive Hi, continued surveillance of all Hi strains is justified.

Developmental immunology and vaccines: Immune responses to vaccines in premature infants

A comparatively small number of studies have assessed the safety, immunogenicity, efficacy and duration of immune responses in preterm infants compared with term infants for routinely recommended childhood immunizations.

Invasive Haemophilus influenzae serotype e and f disease, England and Wales

Incidence of serotype e was 3-fold lower than serotype f, but it caused more severe clinical disease.

Epiglottitis in a Vaccinated Child: A Lifesaving Diagnosis

Epiglottitis is inflammation and cellulitis of the soft tissues above the glottis – the epiglottis, vallecula, arytenoid cartilage and aryepiglottic folds. It is a life-threatening emergency which is most commonly caused by the bacteria Haemophilus influenzae type b. The incidence of epiglottitis has declined dramatically since the introduction of the Haemophilus influenzae type b vaccine and can thus be easily overlooked in the emergency setting. Our case highlights the importance of epiglottitis as a differential diagnosis in the child with acute respiratory distress.

Two decades of experience with the Haemophilus influenzae serotype b conjugate vaccine in the United Kingdom

BACKGROUND

The Haemophilus influenzae serotype b (Hib) conjugate vaccine was introduced into the UK national childhood immunization program in 1992 after clinical trials reported the vaccine to be highly immunogenic in infants as young as two months of age.

OBJECTIVE

The goal of this study was to describe and comment on the impact of routine Hib immunization on the epidemiology of invasive Hib disease in the United Kingdom. In addition, the development of Hib polysaccharide and conjugate vaccines was reviewed.

METHODS

A literature search was conducted of PubMed for invasive Hib disease epidemiology in the United Kingdom. The UK Health Protection Agency Web site was also searched for relevant publications.

RESULTS

The incidence of invasive Hib incidence in children aged <5 years fell from 21/100,000 to 44/100,000 in the prevaccine era to 0.63/100,000 in 1998, with an estimated vaccine failure rate of 2.2/100,000 vaccinees. After 1999, however, invasive Hib disease increased, particularly in toddlers, and peaked in 2003. Potential reasons for the resurgence included a greater-than-expected decline in Hib antibodies after primary immunization, waning of herd immunity offered by the initial catch-up campaign, and use of a less immunogenic Hib combination vaccine containing acellular pertussis in 2000-2001. In response to the resurgence, a Hib combination vaccine containing whole-cell pertussis was reintroduced in 2002, followed by a childhood Hib booster campaign in 2003. In 2004, the recommended infant vaccine was changed to a different Hib/acellular pertussis combination vaccine containing inactivated polio, which had a satisfactory Hib response, was less reactogenic, and eliminated the risk of vaccine-associated paralytic poliomyelitis. This action was followed by introduction of a routine 12-month Hib booster in 2006. Together, these measures led to a decline in invasive Hib disease across all age groups. In 2010, there were only 30 invasive Hib cases, with 6 reported in children aged <5 years and no deaths in this age group since 2007.

CONCLUSIONS

Control of Hib disease is currently the best that has been achieved since the introduction of the routine Hib vaccination almost 20 years ago.

The continuing role of Haemophilus influenzae type b carriage surveillance as a mechanism for early detection of invasive disease activity

Prior to the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, Hib was the leading cause of bacterial meningitis in children under five years of age worldwide. In countries that have adopted Hib vaccination schedules, invasive disease has reduced markedly. Oro-naso pharyngeal carriage is recognized as the most significant source of infection. Hib carriage is significantly associated with poverty, such as overcrowding, poor ventilation in houses, lack of running water, and high smoking rates. Additionally, many Indigenous minority groups report high rates of Hib carriage. A resurgence of Hib disease among Alaskan children in the 1990s, lead to a change in approach to eliminate Hib disease and carriage in high-risk populations. This new approach identifies strategies for eliminating Hib disease focusing on the reservoirs of colonization within families and communities. Monitoring Hib carriage continues to offer an early warning system, whereby intervention could prevent invasive disease resurgence.

Combined Haemophilus Influenzae type B-Neisseria meningitidis serogroup C vaccine is immunogenic and well tolerated in preterm infants when coadministered with other routinely recommended vaccines

BACKGROUND

Preterm infants are at greater risk of morbidity from vaccine-preventable diseases. Therefore, their responses to vaccination are of particular interest.

METHODS

In this open, controlled, Spanish multicenter study, we assessed immunogenicity and safety following primary vaccination of 163 preterm infants (n = 56, <31 weeks' gestation; n = 107, 31-36 weeks' gestation) and 150 full-term infants (>36 weeks' gestation), with Haemophilus Influenzae type B (Hib)-MenC-TT, DTaP(diphtheria-tetanus-acellular pertussis vaccine)-HepB-IPV, and PCV7 at 2 to 4-6 months of age followed by booster vaccination at 16 to 18 months of age. Serum bactericidal activity (rabbit complement) against MenC, and antibodies to Hib and hepatitis b (anti-HBs) were determined. Local/general symptoms were assessed after each vaccination via diary cards. Serious adverse events were recorded throughout the study.

RESULTS

There were no statistically significant differences between preterm and full-term infants in either Hib or MenC seroprotection rates or geometric mean concentrations at 1 month postdose 3, before or 1 month postbooster. Postdose 3, >99% of participants had seroprotective anti-HBs antibody concentrations. Anti-HBs geometric mean concentrations was significantly lower in the <31-week group compared with other groups and this difference persisted until 16 to 18 months of age. Hib-MenC-TT vaccine was well tolerated at all ages. There was one death caused by meningococcal serogroup-B sepsis (full term). No serious adverse events were assessed by the investigator as being vaccine related.

CONCLUSIONS

Hib-MenC-TT vaccine had a similar immunogenicity and safety profile in preterm and full-term infants. These results demonstrate that preterm infants can be safely vaccinated with Hib-MenC-TT at the recommended chronologic age without impacting the responses to the Hib and MenC antigens.

The impact of Haemophilus influenzae serotype B resurgence on the epidemiology of childhood invasive Haemophilus influenzae disease in England and Wales

This study describes the epidemiology of childhood invasive Haemophilus influenzae disease in England and Wales between 1994 and 2008. H. influenzae serotype b incidence was lowest in 1998 (0.26/100,000), rising to 1.8/100,000 in 2002 before falling to 0.27/100,000 in 2008. During this period, nontype b H. influenzae disease remained stable, but there was a small year-on-year increase (3.4%/y; 95% CI: 1.4-5.5%) in incidence.

Immunoglobulin G deficiency in United kingdom children with invasive pneumococcal disease

BACKGROUND

This study aimed to determine whether nonprotective, convalescent pneumococcal serotype-specific immunoglobulin G (IgG) concentrations in children with invasive pneumococcal disease (IPD) might be associated with an underlying IgG deficiency.

METHODS

The first 200 convalescent blood samples from children with IPD that were submitted for pneumococcal antibody testing also had total serum IgG concentrations measured. Pneumococcal IgG testing was performed for 12 serotypes (1, 3, 5, 7, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F); serotype-specific pneumococcal IgG concentrations <0.35 μg/mL were considered nonprotective. IgG deficiency was defined as total serum IgG ≥2 standard deviations below the mean for age.

RESULTS

Nineteen of 172 children (11.0%) with sufficient serum had IgG deficiency although serum IgG concentrations were only marginally below the lower limit for age and all 19 had IgG concentrations >2.0 g/L. IgG deficiency was associated with younger age at disease (median, 5.2 [interquartile range, 2.3-13.5] vs. 12.5 [7.4-17.0] months; P = 0.005) and nonprotective convalescent antibody concentrations against the infecting serotype (10/13 [77%] vs. 51/105 [49%]; P = 0.05). There was a correlation between IgG deficiency and the number of serotypes against which children had nonprotective pneumococcal antibody concentrations, particularly among vaccinated cases (P < 0.05). Vaccine failure was also twice as common among those with IgG deficiency (3/19 [16%] vs. 11/53 [7%], P = 0.20), although this association was not statistically significant. Three children with IgG deficiency who were retested 3 to 5 months later had normal serum IgG concentrations.

CONCLUSIONS

Although 11% of children with IPD had IgG deficiency, total serum IgG concentrations were reassuringly only marginally below the reference range and were within the normal range in those who were retested, suggesting a transient deficiency rather than a serious underlying primary immunodeficiency.

Parents' attitudes to neonatal research involving venepuncture

The objective of the study was to explore parental experiences of being offered participation in a previous neonatal research study involving venepuncture. The method employed was a questionnaire-based exploration of parents' attitudes in those approached to participate in a study of term and preterm immunization responses (Preterm Immunisation Study [PREMIS]). We explored experience of the initial approach, knowledge of study, venepuncture and views on research ‘in general’. In all, 59% of families responded. Highest response rates were for those participating in PREMIS (87% term/69% preterm) and lowest in decliners (34% and 35%). Responding parents participating in PREMIS were well informed, positive about research and did not find the venepuncture problematic. Sixty percent of responding parents who declined PREMIS attributed their declining to the need for venepuncture. In conclusion, parents participating or declining a neonatal study involving venepuncture are different, but participating parents were well informed and seemed able to judge that participation was right for them such that in consenting families venepuncture itself is not problematic.

Low serum serotype-specific pneumococcal antibody concentrations in young children with Haemophilus influenzae serotype b (Hib) vaccine failure

Serotype-specific pneumococcal antibody concentrations were measured in 164 children with Hib vaccine failure prior to routine pneumococcal immunisation. Compared with age-matched controls, a higher proportion of cases had non-protective antibody concentrations (< 0.35 microg/ml) for 7/9 (78%) serotypes tested among 2-4 year-olds, 4/9 (44%) among 5-7 year-olds, 1/9 (11%) among 8-11 year-olds and 0/9 (0%) among 12-15 year-olds (chi(2) for trend=14.0, p=0.0002). Cases aged 2-4 years were also more likely to have non-protective antibody concentrations against more serotypes than controls, suggesting that children with Hib vaccine failure may have an intact but physiologically delayed ability to develop protective antibody concentrations against encapsulated organisms.

Long-term complications and risk of other serious infections following invasive Haemophilus influenzae serotype b disease in vaccinated children

This study describes the long-term complications in children with Haemophilus influenzae serotype b (Hib) vaccine failure and to determine their risk of other serious infections. The families of 323 children with invasive Hib disease after appropriate vaccination (i.e. vaccine failure) were contacted to complete a questionnaire relating to their health and 260 (80.5%) completed the questionnaire. Of the 124 children with meningitis, 18.5% reported serious long-term sequelae and a further 12.1% of parents attributed other problems to Hib meningitis. Overall, 14% (32/231 cases) of otherwise healthy children and 59% (17/29 cases) of children with an underlying condition developed at least one other serious infection requiring hospital admission. In a Poisson regression model, the risk of another serious infection was independently associated with the presence of an underlying medical condition (incidence risk ratio (IRR) 7.6, 95% CI 4.8-12.1; p<0.0001), both parents having had a serious infection (IRR 4.1, 95% CI 1.6-10.3; p=0.003), requirement of more than two antibiotic courses per year (IRR 2.3, 95% CI 1.4-3.6; p=0.001) and the presence of a long-term complication after Hib infection (IRR 1.8, 95% CI 1.1-3.1; p=0.03). Thus, rates of long-term sequelae in children with vaccine failure who developed Hib meningitis are similar to those in unvaccinated children in the pre-vaccine era. One in seven otherwise healthy children (14%) with Hib vaccine failure will go on to suffer another serious infection requiring hospital admission in childhood, which is higher than would be expected for the UK paediatric population.

Haemophilus influenzae serotype b conjugate vaccine failure in twelve countries with established national childhood immunization programmes

The present study describes the clinical and immunological features of children with Hib vaccine failure, who were identified through national surveillance between 1996 and 2001 in Europe, Israel and Australia. True vaccine failure was defined as invasive Hib disease occurring ≥2 weeks after one dose, given after the first birthday, or ≥1 week after ≥2 doses, given at <1 year of age. Of the 423 cases (representing 0.2 cases per 100,000 child-years at risk) reported, 330 (78%) had received three doses in the first year of life and developed disease at a median age of 28 months. Of the remaining 93, 48 had received two doses in infancy, 34 had received four doses including a booster, and 11 had received a single dose after 12 months of age. These children developed disease at a median age of 12, 33 and 71 months, respectively. In total, 47 out of 258 children (18%) with available information had an underlying medical problem (including prematurity) and 53 out of 161 (33%) had immunoglobulin deficiency. Convalescent Hib antibody concentrations were above the putative protective concentration of 1.0 mg/L in 147/194 (76%) children; low concentrations were associated with both the presence of an underlying medical problem and young age at the time of Hib disease. Almost all children who received an additional vaccine dose developed antibodies at protective concentrations. Thus, Hib vaccine failure is rare, but can occur with any immunization schedule. Children with Hib vaccine failure should have immunoglobulin and convalescent Hib antibody concentrations measured after infection and receive additional vaccination, if required.

Hib epiglottitis despite fully vaccinated status

The introduction of an effective vaccine has markedly reduced the incidence of invasive Haemophilus influenzae type b (Hib) disease. However, vaccination failure can occur, and this report describes one such case in a previously healthy 4-year-old girl, who became severely unwell with Hib epiglottitis. She had received a full course of Hib vaccine administered via the buttocks. This site has been associated with reduced immunogenicity compared to vaccination by injection into the thigh or deltoid muscles. Current recommendations are to avoid gluteal injection for all vaccinations.

Update in understanding common variable immunodeficiency disorders (CVIDs) and the management of patients with these conditions

The common variable immunodeficiency disorders are a mixed group of heterogeneous conditions linked by lack of immunoglobulin production and primary antibody failure. This variability results in difficulty in making coherent sense of either immunopathogenesis or the role of various genetic abnormalities reported in the literature. The recent attempt to collate the varied complications in these conditions and to define particular clinical phenotypes has improved our understanding of these diseases. Once refined and confirmed by other studies, these definitions will facilitate improved accuracy of prognosis and better management of clinical complication. They may also provide a method of analysing outcomes as related to new immunopathological and genetic findings.