Do we need a booster of Hib vaccine after primary vaccination? A study on anti-Hib seroprevalence in Sweden 5 and 15 years after the introduction of universal Hib vaccination related to notifications of invasive disease

Haemophilus influenzae type b disease in the era of conjugate vaccines: critical factors for successful eradication

INTRODUCTION

Prior to implementation of Haemophilus influenzae type b (Hib)-conjugate vaccination programs in the 1990s, Hib was the commonest cause of bacterial meningitis in children aged <5 years. While the burden of all Hib disease has significantly decreased in the post-vaccination era, Hib still accounted for >29,000 deaths worldwide in children aged <5 years in 2015.

AREAS COVERED

We reviewed literature data on the most widely used Hib vaccines and vaccination strategies which led to the global prevention and control of Hib disease and aim to highlight important factors for continued disease control and elimination in the future.

EXPERT COMMENTARY

More than 90% of countries worldwide have implemented Hib-conjugate vaccination in their national immunization programs. Vaccines containing Hib polyribosylribitol phosphate (PRP) conjugated with tetanus toxoid (Hib-TT) are the most commonly used. Neisseria meningitidis outer membrane protein complex of PRP (Hib-OMP) is also used. Although the kinetics of the immune response varies with Hib vaccine and schedule used, high control of Hib disease was observed in all settings/scenarios. Further improving global Hib vaccination coverage may result in disease elimination. Plain language summary What is the context? Haemophilus influenzae is causing a variety of diseases, from otitis media and sinusitis to invasive disease (e.g. meningitis and pneumonia). H. influenzae type b (Hib) was the most common cause of bacterial meningitis in children <5 years of age, and especially among <2-year-olds. Even with appropriate treatment, up to 40% of children with bacterial meningitis can suffer permanent disabilities and up to 5% will die. The development of vaccines to protect against Hib disease has started in the late 1970s and has culminated with the licensure of 4 Hib conjugate vaccines, of which 2 are currently widely used. What is new? In this review, we gathered evidence on the different Hib vaccines and vaccination strategies that have contributed to the global prevention and control of Hib disease. The review indicates: the incidence of Hib disease has decreased considerably due to the introduction of Hib vaccines in national immunization programs worldwide. However, Hib disease is not yet completely eradicated. the vaccines currently used offer protection against Hib over long periods of time. carriage of the pathogen by healthy individuals seem to be less frequent, but data are still needed to fully evaluate the impact of vaccination. other H. influenzae types are now more frequent. Why is this important? Despite the huge success of Hib vaccination, continuous surveillance is needed to anticipate potential re-emergences and devise the best strategies for prevention and control of disease. Hib vaccination should be considered in the few countries who have not yet implemented it, to decrease associated morbidity and mortality.

A review of Haemophilus influenzae disease in Europe from 2000-2014: challenges, successes and the contribution of hexavalent combination vaccines

INTRODUCTION

The development of diphtheria-tetanus-acellular pertussis-Haemophilus influenzae type b (Hib) conjugate vaccine combinations culminated with hexavalent vaccines, the largest, most complex vaccine combinations in the immunization calendar. Hexavalent vaccines are used widely in Europe and are co-administered with multiple other recommended vaccines. Hib immunogenicity may reduce when combined with acellular pertussis antigens, or in some co-administrations. We reviewed the epidemiology of H. influenzae disease in Europe aiming to evaluate the current level of Hib control and indirectly assess the effectiveness against Hib of GSK's hexavalent vaccine in 10 countries where it is/has been used almost exclusively. Areas covered: We reviewed surveillance data from the European Union Invasive Bacterial Infections Surveillance Network and the European Surveillance System database from 1999-2014 and extracted case and incidence/notification rates (per 100,000 population) of invasive H. influenzae disease. We included age and serotype/strains distribution among countries in the European Union/European Economic Area region that reported to the European Centre for Disease Prevention and Control surveillance system. Expert commentary: The impact of Hib vaccination in Europe is sustained, testifying to continued effectiveness against invasive Hib disease after the implementation of hexavalent vaccines into immunization programs, which, since 2006, has been almost exclusively GSK´s hexavalent DTPa-HBV-IPV/Hib vaccine.

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.

Immunological persistence in 5 y olds previously vaccinated with hexavalent DTPa-HBV-IPV/Hib at 3, 5, and 11 months of age

The combined diphtheria-tetanus-acellular pertussis-hepatitis B-poliomyelitis/Haemophilus influenza vaccine (DTPa-HBV-IPV/Hib: Infanrix™ hexa, GlaxoSmithKline Vaccines) is used for primary vaccination of infants in a range of schedules world-wide. Antibody persistence after 4 DTPa-HBV-IPV/Hib doses in the first 2 y of life has been documented, but long-term persistence data following the 3, 5, 11–12 months (3–5–11) infant vaccination schedule, employed for example in Nordic countries, are limited. We assessed antibody persistence in 57 5-year-old children who had received either DTPa-HBV-IPV/Hib or DTPa-IPV/Hib (Infanrix™-IPV/Hib, GlaxoSmithKline Vaccines) in the 3–5–11 schedule. Among DTPa-HBV-IPV/Hib recipients, 7/12 retained seroprotective antibody concentrations for diphtheria, 10/12 for tetanus, 5/12 for hepatitis and 10/12 for Hib. Detectable antibodies were observed for 0/12 children for pertussis toxin (PT), 12/12 for filamentous haemagglutinin (FHA) and 8/12 for pertactin (PRN). Among DTPa-IPV/Hib recipients, 28/45 retained seroprotective anti-diphtheria concentrations, 34/44 for tetanus and 40/45 for Hib. Detectable antibodies were observed for 9/45 children for PT, 41/45 for FHA and 34/45 for PRN. Antibody persistence in DTPa-HBV-IPV/Hib and DTPa-IPV/Hib-vaccinees appeared similar in 5 y olds to that previously observed in children of a similar age who had received 4 prior doses of DTPa-HBV-IPV/Hib (or DTPa-IPV/Hib). As in subjects primed with 4 prior doses, we observed that antibodies markedly declined by 5 y of age, calling for the administration of a pre-school booster dose in order to ensure continued protection against pertussis.

Splenectomy and the risk of sepsis: a population-based cohort study

OBJECTIVE

We sought to estimate the long-term risk of sepsis in patients who underwent splenectomy before, during, and after implementation of vaccination.

BACKGROUND

Because patients who have undergone splenectomy are considered at increased risk of bacterial sepsis, they typically receive vaccination, education, and occasionally antibiotic prophylaxis. However, the extent to which these interventions have actually reduced the risk of sepsis remains unclear.

METHODS

Retrospective cohort study encompassing all patients in the Swedish national inpatient register, who underwent splenectomy in 1970-2009. Patients were followed for hospitalization for or death from sepsis, as identified using national inpatient and cause of death registers. Relative risks, comparing patients to the background population were expressed as standardized incidence ratios (SIRs) and standardized mortality ratios (SMRs).

RESULTS

Altogether, 20,132 splenectomized patients were included. The overall SIR for hospitalization for sepsis was 5.7 [95% confidence interval (CI), 5.6-6.0]. However, risks depended on the indication for splenectomy, with SIRs varying from 3.4 (95% CI, 3.0-3.8) for trauma patients to 18 (95% CI, 16-19) for patients with hematologic malignancies. SMRs ranged from 3.1 (95% CI, 2.1-4.3) for trauma to 8.7 (95% CI, 6.8-11) for hematologic disease. In regression analyses adjusting for age at splenectomy, follow-up time, sex, and calendar year of splenectomy, there were no significant risk decreases after implementation of routine vaccination, except for in patients with malignant and non-malignant hematologic disease.

CONCLUSIONS

The risk of hospitalization or death from sepsis is high in patients who previously underwent splenectomy and depends on the indication for splenectomy. The effectiveness of current vaccination practices warrants further evaluation.

Combined hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus-Haemophilus influenzae type B vaccine; Infanrix™ hexa: twelve years of experience in Italy

Infant vaccination using 2-dose priming at 3 and 5 mo of age with a booster at 11–12 mo of age was pioneered in Italy. The 3-5-11 schedule is now used in a growing number of European countries. Infanrix™ hexa (DTPa-HBV-IPV/Hib, GlaxoSmithKline Vaccines) was first licensed for use in 2000 and has been the only pediatric hexavalent vaccine available since 2005. We reviewed available clinical trial data describing the immunogenicity of DTPa-HBV-IPV/Hib when administered at 3, 5, and 11 mo of age, and conducted an analysis of safety using global and Italian post-marketing surveillance data. In Italy, DTPa-HBV-IPV/Hib has a demonstrated safety record extending over a decade of use, it has been associated with record levels of vaccine coverage, and with sustained disease control in vaccinated cohorts. Hexavalent vaccines will continue to contribute to high vaccine coverage in Italy and across Europe.

Risk of invasive Haemophilus influenzae type b (Hib) disease in adults with secondary immunodeficiency in the post-Hib vaccine era

Prior to the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, invasive Hib disease affected almost exclusively children. According to some recent studies, in the postvaccine era, adults, the elderly, and immunocompromised persons can be affected more often than children. As the production of type-specific anti-capsular polysaccharide antibodies is the major defense mechanism against Hib, individuals with defects in humoral immune responses have high susceptibility to infections caused by Hib. We hypothesized that nonvaccinated adults with chronic conditions causing immunosuppression may lack protective antibody to Hib. We assessed serum anti-Hib IgG levels and bactericidal activity in 59 patients with chronic renal failure, 30 patients with type 2 diabetes mellitus, 28 patients with chronic obstructive pulmonary disease (COPD), and 20 patients with multiple myeloma compared to 32 healthy controls of similar age. Considering antibody at >0.15 μg/ml as the protective correlate in unvaccinated individuals, we detected subprotective Hib antibody levels in 29% of chronic renal failure, 20% of diabetes, 14% of COPD, and 55% of myeloma patients compared to 3% of healthy controls. Additionally, 70% of myeloma and 58% of chronic renal failure patients did not have detectable serum bactericidal activity against Hib. Among individuals with severe diseases causing secondary immunodeficiency, patients with multiple myeloma and chronic renal failure are at an increased risk of invasive Hib disease. Considering that Hib continues to circulate in the population, this study provides a rationale for the immunization of some adult patients with secondary immunodeficiency with the pediatric Hib vaccine to achieve protective immunity.

Glycoconjugate vaccines and immune interactions, and implications for vaccination schedules

Conjugate vaccines using diphtheria toxoid variant (CRM(197)), diphtheria toxoid and tetanus toxoid (TT) as carrier protein may induce immune interactions (interference or impairment as measured by lower antibody levels, or enhancement [higher antibody levels]) when coadministered with other vaccines. Immune enhancement occurs when two TT conjugates are coadministered. CRM(197) conjugate vaccines induce immune bystander interference when given with diphtheria-tetanus-acellular pertussis vaccines, which reduces responses to coadministered Haemophilus influenzae type b vaccine conjugated to TT. These bystander effects are greater as the amount of CRM(197) administered increases. When large amounts of either TT or CRM(197) are coadministered, dose-related carrier-induced epitopic suppression may occur, affecting immune responses to meningococcal or pneumococcal polysaccharides. These observations have implications for vaccine scheduling. The range of available alternative vaccines means that specific vaccine coadministrations can avoid or reduce CRM(197)-induced interference. Potential interactions arising from new CRM(197) or TT conjugates will need to be thoroughly examined.

Immunogenicity of Infanrix™ hexa administered at 3, 5 and 11 months of age

A pooled analysis of data from four vaccination studies conducted in Europe was undertaken to assess the immunogenicity of Infanrix™ hexa (DTPa-HBV-IPV/Hib, GlaxoSmithKline Biologicals) when administered in a total of 702 healthy infants at 3, 5 and 11-12 months of age. One month after dose 2, between 96.3% and 100% of subjects had seroprotective antibodies against diphtheria, tetanus, hepatitis B and poliovirus types 1, 2 and 3; 91.7% against Hib and ≥99.0% were seropositive for each pertussis antigen. One month after the third dose, 98.9-100% of subjects were seroprotected/seropositive for all vaccine antigens. Geometric mean antibody concentrations/titres for each vaccine antigen increased by 6.7-52.9 fold after the third vaccine dose. No serious adverse events in DTPa-HBV-IPV/Hib recipients were vaccine related. Infanrix™ hexa induces an adequate immune response after 2-dose primary plus booster doses when administered according to a 3, 5 and 11 months schedule.

Update on childhood and adolescent immunizations: selected review of US recommendations and literature: part 1

PURPOSE OF REVIEW

To provide a clinically relevant synopsis of research findings regarding childhood and adolescent vaccines.

RECENT FINDINGS

Much research confirms the safety, immunogenicity, and efficacy of specific vaccines as well as the positive impact on overall morbidity and mortality. Prevention and control strategies involve the expansion of vaccine recommendations to include more individuals and/or more vaccine doses. In addition, the role of universal infant vaccination, the advantages of even partial immunization, and the documented benefits of recently introduced vaccines are explored. The material in this review includes important areas of clinical practice improvement, such as awareness of interim recommendations or monitoring of vaccine failures. Literature on hepatitis B, rotavirus, Haemophilus influenzae type b conjugate, and pneumococcal vaccines is included in this first of two articles.

SUMMARY

New research on childhood and adolescent vaccines is anticipated to shape the practice of pediatric providers. Research will continue to provide the science to optimize protection and to promote the health and well being of all children and adolescents.