Conjugate Haemophilus influenzae type b vaccines for sickle cell disease

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 We also searched trial registries (04 July 2018) and contacted relevant pharmaceutical companies to identify unpublished trials.Date of last search of the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinoapthies Trials Register: 18 December 2017.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.

Effects of vaccines in patients with sickle cell disease: a systematic review protocol

INTRODUCTION

Sickle cell disease (SCD) is an inherited haematological disorder caused by a single point mutation (Glub6Val) that promotes polymerisation of haemoglobin S and sickling of erythrocytes. Inflammation, haemolysis, microvascular obstruction and organ damage characterise the highly variable clinical expression of SCD. People with SCD are at increased risk of severe infections, hence the need for vaccination against common disease-causing organisms in this population. We aim to review the evidence on the efficacy and safety of vaccines in people with SCD.

METHODS AND ANALYSIS

The present systematic review will examine the current data as indexed in PubMed, CENTRAL, EMBASE and EBSCOHost. We will consult Strategic Advisory Group of Experts practice statements, conference abstracts, reference lists of relevant articles, WHO ICTRP trial registry and experts in the field. Two authors will independently screen search outputs, select studies, extract data and assess risk of bias; resolving discrepancies by discussion and consensus between the two authors or arbitration by a third author when necessary. We will perform a meta-analysis for clinically homogenous studies. Evidence from clinically diverse studies will be aggregated using narrative synthesis of the findings. In either case, we will use the GRADE approach to assess the strength of the available evidence.

ETHICS AND DISSEMINATION

The study draws on data that are readily available in the public domain, hence no formal ethical review and approval is required. The findings of this review will be disseminated through conference presentations and a publication in a peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

CRD42018084051.

Alteration of lymphocyte phenotype and function in sickle cell anemia: Implications for vaccine responses

Individuals with sickle cell anemia (SCA) have increased susceptibility to infections, secondary to impairment of immune function. Besides the described dysfunction in innate immunity, including impaired opsonization and phagocytosis of bacteria, evidence of dysfunction of T and B lymphocytes in SCA has also been reported. This includes reduction in the proportion of circulating CD4+ and CD8+ T cells, reduction of CD4+ helper: CD8+ suppressor T cell ratio, aberrant activation and dysfunction of regulatory T cells (Treg ), skewing of CD4+ T cells towards Th2 response and loss of IgM-secreting CD27 + IgM(high) IgD(low) memory B cells. These changes occur on the background of immune activation characterized by predominance of memory CD4+ T cell phenotypes, increased Th17 signaling and elevated levels of C-reactive protein and pro-inflammatory cytokines IL-6 and TNF-α, which may affect the immunogenicity and protective efficacy of vaccines available to prevent infections in SCA. Thus, in order to optimize the use of vaccines in SCA, a thorough understanding of T and B lymphocyte functions and vaccine reactivity among individuals with SCA is needed. Studies should be encouraged of different SCA populations, including sub-Saharan Africa where the burden of SCA is highest. This article summarizes our current understanding of lymphocyte biology in SCA, and highlights areas that warrant future research. Am. J. Hematol. 91:938-946, 2016. © 2016 Wiley Periodicals, Inc.