Response to conjugate Haemophilus influenzae B vaccine among infants in Niamey, Niger

Pediatric Bacterial Meningitis Surveillance in Niger: Increased Importance of Neisseria meningitidis Serogroup C, and a Decrease in Streptococcus pneumoniae Following 13-Valent Pneumococcal Conjugate Vaccine Introduction

BACKGROUND

Meningitis is endemic in Niger. Haemophilus influenzae type b (Hib) vaccine and the 13-valent pneumococcal conjugate vaccine (PCV13) were introduced in 2008 and 2014, respectively. Vaccination campaign against Neisseria meningitidis serogroup A was carried out in 2010-2011. We evaluated changes in pathogen distribution using data from hospital-based surveillance in Niger from 2010 through 2016.

METHODS

Cerebrospinal fluid (CSF) specimens from children <5 years old with suspected meningitis were tested to detect vaccine-preventable bacterial pathogens. Confirmatory identification and serotyping/grouping of Streptococcus pneumoniae, N. meningitidis, and H. influenzae were done. Antimicrobial susceptibility testing and whole genome sequencing were performed on S. pneumoniae isolates.

RESULTS

The surveillance included 2580 patients with suspected meningitis, of whom 80.8% (2085/2580) had CSF collected. Bacterial meningitis was confirmed in 273 patients: 48% (131/273) was N. meningitidis, 45% (123/273) S. pneumoniae, and 7% (19/273) H. influenzae. Streptococcus pneumoniae meningitis decreased from 34 in 2014, to 16 in 2016. PCV13 serotypes made up 88% (7/8) of S. pneumoniae meningitis prevaccination and 20% (5/20) postvaccination. Neisseria meningitidis serogroup C (NmC) was responsible for 59% (10/17) of serogrouped N. meningitidis meningitis. Hib caused 67% (2/3) of the H. influenzae meningitis isolates serotyped. Penicillin resistance was found in 16% (4/25) of S. pneumoniae isolates. Sequence type 217 was the most common lineage among S. pneumoniae isolates.

CONCLUSIONS

Neisseria meningitidis and S. pneumoniae remain important causes of meningitis in children in Niger. The decline in the numbers of S. pneumoniae meningitis post-PCV13 is encouraging and should continue to be monitored. NmC is the predominant serogroup causing N. meningitidis meningitis.

Molecular detection of respiratory pathogens among children aged younger than 5 years hospitalized with febrile acute respiratory infections: A prospective hospital-based observational study in Niamey, Niger

BACKGROUND AND AIMS

In Niger, acute respiratory infections (ARIs) are the second most common cause of death in children aged younger than 5 years. However, the etiology of ARI is poorly understood in the country. This study aims to describe viral and bacterial infections among children aged younger than 5 years hospitalized with febrile ARI at two hospitals in Niamey, Niger's capital city, and the reported clinical procedures.

METHODS

We conducted a prospective study among children aged younger than 5 years hospitalized with febrile ARI at two national hospitals in Niamey between January and December 2015. Clinical presentation and procedures during admission were documented using a standardized case investigation form. Nasopharyngeal specimens collected from each patient were tested for a panel of respiratory viruses and bacteria using the Fast Track Diagnostic 21 Plus kit.

RESULTS

We enrolled and tested 638 children aged younger than 5 years, of whom 411 (64.4%) were aged younger than 1 year, and 15 (2.4%) died during the study period. Overall, 496/638 (77.7%) specimens tested positive for at least one respiratory virus or bacterium; of these, 195 (39.3%) tested positive for respiratory viruses, 126 (25.4%) tested positive for respiratory bacteria, and 175 (35.3%) tested positive for both respiratory viruses and bacteria. The predominant viruses detected were respiratory syncytial virus (RSV) (149/638; 23.3%), human parainfluenza virus (HPIV) types 1 to 4 (78/638; 12.2%), human rhinovirus (HRV) (62/638; 9.4%), human adenovirus (HAV) (60/638; 9.4%), and influenza virus (INF) (52/638; 8.1%). Streptococcus pneumoniae (249/638; 39.0%) was the most frequently detected bacterium, followed by Staphylococcus aureus (112/638; 12.2%) and Haemophilus influenzae type B (16/638; 2.5%). Chest X-rays were performed at the discretion of the attending physician on 301 (47.2%) case patients. Of these patients, 231 (76.7%) had abnormal radiological findings. A total of 135/638 (21.2%) and 572/638 (89.7%) children received antibiotic treatment prior to admission and during admission, respectively.

CONCLUSION

A high proportion of respiratory viruses was detected among children aged younger than 5 years with febrile ARI, raising concerns about excessive use of antibiotics in Niger.

Immunization Coverage Surveys and Linked Biomarker Serosurveys in Three Regions in Ethiopia

Objective

Demographic and health surveys, immunization coverage surveys and administrative data often divergently estimate vaccination coverage, which hinders pinpointing districts where immunization services require strengthening. We assayed vaccination coverage in three regions in Ethiopia by coverage surveys and linked serosurveys.

Methods

Households with children aged 12–23 (N = 300) or 6–8 months (N = 100) in each of three districts (woredas) were randomly selected for immunization coverage surveys (inspection of vaccination cards and immunization clinic records and maternal recall) and linked serosurveys. IgG-ELISA serologic biomarkers included tetanus antitoxin ≥ 0.15 IU/ml in toddlers (receipt of tetanus toxoid) and Haemophilus influenzae type b (Hib) anti-capsular titers ≥ 1.0 mcg/ml in infants (timely receipt of Hib vaccine).

Findings

Coverage surveys enrolled 1,181 children across three woredas; 1,023 (87%) also enrolled in linked serosurveys. Administrative data over-estimated coverage compared to surveys, while maternal recall was unreliable. Serologic biomarkers documented a hierarchy among the districts. Biomarker measurement in infants provided insight on timeliness of vaccination not deducible from toddler results.

Conclusion

Neither administrative projections, vaccination card or EPI register inspections, nor parental recall, substitute for objective serological biomarker measurement. Including infants in serosurveys informs on vaccination timeliness.

Effect of Haemophilus influenzae type b vaccination without a booster dose on invasive H influenzae type b disease, nasopharyngeal carriage, and population immunity in Kilifi, Kenya: a 15-year regional surveillance study

BACKGROUND

Haemophilus influenzae type b (Hib) conjugate vaccine, delivered as a three-dose series without a booster, was introduced into the childhood vaccination programme in Kenya in 2001. The duration of protection and need for a booster dose are unknown. We aimed to assess vaccine effectiveness, the impact of the vaccine on nasopharyngeal carriage, and population immunity after introduction of conjugate Hib vaccine in infancy without a booster dose in Kenya.

METHODS

This study took place in the Kilifi Health and Demographic Surveillance System (KHDSS), an area of Kenya that has been monitored for vital events and migration every 4 months since 2000. We analysed sterile site cultures for H influenzae type b from children (aged ≤12 years) admitted to the Kilifi County Hospital (KCH) from Jan 1, 2000, through to Dec 31, 2014. We determined the prevalence of nasopharyngeal carriage by undertaking cross-sectional surveys in random samples of KHDSS residents (of all ages) once every year from 2009 to 2012, and measured Hib antibody concentrations in five cross-sectional samples of children (aged ≤12 years) within the KHDSS (in 1998, 2000, 2004-05, 2007, and 2009). We calculated incidence rate ratios between the prevaccine era (2000-01) and the routine-use era (2004-14) and defined vaccine effectiveness as 1 minus the incidence rate ratio, expressed as a percentage.

FINDINGS

40,482 children younger than 13 years resident in KHDSS were admitted to KCH between 2000 and 2014, 38,206 (94%) of whom had their blood cultured. The incidence of invasive H influenzae type b disease in children younger than 5 years declined from 62·6 (95% CI 46·0-83·3) per 100,000 in 2000-01 to 4·5 (2·5-7·5) per 100,000 in 2004-14, giving a vaccine effectiveness of 93% (95% CI 87-96). In the final 5 years of observation (2010-14), only one case of invasive H influenzae type b disease was detected in a child younger than 5 years. Nasopharyngeal H influenzae type b carriage was detected in one (0·2%) of 623 children younger than 5 years between 2009 and 2012. In the 2009 serosurvey, 92 (79%; 95% CI 70-86) of 117 children aged 4-35 months had long-term protective antibody concentrations.

INTERPRETATION

In this region of Kenya, use of a three-dose primary series of Hib vaccine without a booster dose has resulted in a significant and sustained reduction in invasive H influenzae type b disease. The prevalence of nasopharyngeal carriage is low and the profile of Hib antibodies suggests that protection wanes only after the age at greatest risk of disease. Although continued surveillance is important to determine whether effective control persists, these findings suggest that a booster dose is not currently required in Kenya.

FUNDING

Gavi, the Vaccine Alliance, Wellcome Trust, European Society for Paediatric Infectious Diseases, and National Institute for Health Research.

Two or three primary dose regime for Haemophilus influenzae type b conjugate vaccine: meta-analysis of randomized controlled trials

Haemophilus influenzae type b (Hib) is an important cause of meningitis and pneumonia in children. Despite the availability of Hib conjugate vaccine, many countries are still to implement it in their immunization schedule. Before introducing the vaccine in routine immunization programs, it is important to know not only the cumulative efficacy but also the efficacy of each vaccine dose. The primary objective of this review is to find whether two primary dose schedule of Hib vaccine is equally efficacious as the standard three primary dose schedule. A highly sensitive online search was run using the terms 'Haemophilus Vaccines' or 'Haemophilus influenzae type b' and 'conjugate vaccine', and Medline (Ovid), PubMed, Embase, CENTRAL and Scopus were explored for prospective randomized controlled studies. Data were extracted in a predesigned proforma and analyzed using RevMan software. Nine randomized studies were included in the analysis. Pooled vaccine efficacy using a fixed effects model against confirmed invasive Hib disease following the 3, 2 and 1 primary dose schedule were 82% [95% confidence interval (CI) 73-87], 79% (95% CI 54-90) and 65% (95% CI 23-84), respectively, and the overall efficacy was 80% (95% CI 72-85). To conclude, we found that Hib conjugate vaccine is highly efficacious and that the two dose regime is as good as the three dose regime. [The protocol was registered with PROSPERO (CRD42013004490)].

Carrier priming or suppression: understanding carrier priming enhancement of anti-polysaccharide antibody response to conjugate vaccines

INTRODUCTION

With the availability of newer conjugate vaccines, immunization schedules have become increasingly complex due to the potential for unpredictable immunologic interference such as 'carrier priming' and 'carrier induced epitopic suppression'. Carrier priming refers to an augmented antibody response to a carbohydrate portion of a glycoconjugate vaccine in an individual previously primed with the carrier protein. This review aims to provide a critical evaluation of the available data on carrier priming (and suppression) and conceptualize ways by which this phenomenon can be utilized to strengthen vaccination schedules.

METHODS

We conducted this literature review by searching well-known databases to date to identify relevant studies, then extracted and synthesized the data on carrier priming of widely used conjugate polysaccharide vaccines, such as, pneumococcal conjugate vaccine (PCV), meningococcal conjugate vaccine (MenCV) and Haemophilus influenzae type b conjugate vaccines (HibV).

RESULTS

We found evidence of carrier priming with some conjugate vaccines, particularly HibV and PCV, in both animal and human models but controversy surrounds MenCV. This has implications for the immunogenicity of conjugate polysaccharide vaccines following the administration of tetanus-toxoid or diphtheria-toxoid containing vaccine (such as DTP).

CONCLUSION

Available evidence supports a promising role for carrier priming in terms of maximizing the immunogenicity of conjugate vaccines and enhancing immunization schedule by making it more efficient and cost effective.

Prevention ofHaemophilus influenzaetype b disease: past success and future challenges

Haemophilus influenzae type b (Hib) is responsible for significant morbidity and mortality worldwide, particularly in children under 5 years of age. In countries where the Hib conjugate vaccine is not routinely used, Hib is a leading cause of childhood pneumonia and meningitis. Routine use of the Hib conjugate vaccines has resulted in a remarkable decline in Hib disease in developed and developing countries. However, Hib conjugate vaccines are not routinely available in most developing countries, many of which have high burdens of Hib disease. This review outlines the pathogenesis and epidemiology of Hib disease, and the various options for prevention.

Comparing Haemophilus influenzae type b conjugate vaccine schedules: a systematic review and meta-analysis of vaccine trials

BACKGROUND

The optimal schedule and the need for a booster dose are unclear for Haemophilus influenzae type b (Hib) conjugate vaccines. We systematically reviewed relative effects of Hib vaccine schedules.

METHODS

We searched 21 databases to May 2010 or June 2012 and selected randomized controlled trials or quasi-randomized controlled trials that compared different Hib schedules (3 primary doses with no booster dose [3p+0], 3p+1 and 2p+1) or different intervals in primary schedules and between primary and booster schedules. Outcomes were clinical efficacy, nasopharyngeal carriage and immunological response. Results were combined in random-effects meta-analysis.

RESULTS

Twenty trials from 15 countries were included; 16 used vaccines conjugated to tetanus toxoid (polyribosylribitol phosphate conjugated to tetanus toxoid). No trials assessed clinical or carriage outcomes. Twenty trials examined immunological outcomes and found few relevant differences. Comparing polyribosylribitol phosphate conjugated to tetanus toxoid 3p+0 with 2p+0, there was no difference in seropositivity at the 1.0 μg/mL threshold by 6 months after the last primary dose (combined risk difference -0.02; 95% confidence interval: -0.10, 0.06). Only small differences were seen between schedules starting at different ages, with different intervals between primary doses, or with different intervals between primary and booster doses. Individuals receiving a booster were more likely to be seropositive than those at the same age who did not.

CONCLUSIONS

There is no clear evidence from trials that any 2p+1, 3p+0 or 3p+1 schedule of Hib conjugate vaccine is likely to provide better protection against Hib disease than other schedules. Until more data become available, scheduling is likely to be determined by epidemiological and programmatic considerations in individual settings.

Naturally acquired and conjugate vaccine-induced antibody to Haemophilus influenzae type b (Hib) polysaccharide in Malian children: serological assessment of the Hib immunization program in Mali

Haemophilus influenzae type b (Hib) conjugate vaccine for infants (6, 10, and 14 weeks of age) was introduced into the Malian Expanded Program on Immunization in July 2005, to diminish invasive Hib disease in young children. Antibodies to Hib capsular polysaccharide (PRP) were measured in infants and toddlers from an area already served by the Hib immunization program (Bamako) and in unimmunized children of the same age in a district (Kangaba) where Hib immunization had not yet begun. Among vaccinated Bamako children 6-23 months of age, 77-93% exhibited PRP titers ≥ 1.0 μg/mL, indicating long-term protection, versus only 10-23% of Kangaba children of that age. High PRP antibody titers in immunized children persisted through 2 years of age. Moreover, ∼50% of Bamako children exhibited anti-PRP titers ≥ 5.0 μg/mL; a level that impedes Hib upper respiratory carriage, and may thereby diminish the Hib transmission to the unimmunized susceptible population (i.e., providing indirect protection).

Effectiveness of Haemophilus influenzae type b Conjugate vaccine introduction into routine childhood immunization in Kenya

CONTEXT

Haemophilus influenzae type b (Hib) conjugate vaccine is not perceived as a public health priority in Africa because data on Hib disease burden and vaccine effectiveness are scarce. Hib immunization was introduced in Kenyan infants in 2001.

OBJECTIVE

To define invasive Hib disease incidence and Hib vaccine program effectiveness in Kenya.

DESIGN, SETTING, AND PATIENTS

Culture-based surveillance for invasive Hib disease at Kilifi District Hospital from 2000 through 2005 was linked to demographic surveillance of 38,000 children younger than 5 years in Kilifi District, Kenya. Human immunodeficiency virus (HIV) infection and Hib vaccination status were determined for children with Hib disease admitted 2002-2005.

INTERVENTIONS

Introduction of conjugate Hib vaccine within the routine childhood immunization program at ages 6, 10, and 14 weeks beginning November 2001.

MAIN OUTCOME MEASURES

Incidence of culture-proven Hib invasive disease before and after vaccine introduction and vaccine program effectiveness.

RESULTS

Prior to vaccine introduction, the median age of children with Hib was 8 months; case fatality was 23%. Among children younger than 5 years, the annual incidence of invasive Hib disease 1 year before and 1 and 3 years after vaccine introduction was 66, 47, and 7.6 per 100,000, respectively. For children younger than 2 years, incidence was 119, 82, and 16 per 100,000, respectively. In 2004-2005, vaccine effectiveness was 88% (95% confidence interval, 73%-96%) among children younger than 5 years and 87% (95% confidence interval, 66%-96%) among children younger than 2 years. Of 53 children with Hib admitted during 2002-2005, 29 (55%) were age-ineligible to have received vaccine, 12 (23%) had not been vaccinated despite being eligible, and 12 (23%) had received 2 or more doses of vaccine (2 were HIV positive).

CONCLUSIONS

In Kenya, introduction of Hib vaccine into the routine childhood immunization program reduced Hib disease incidence among children younger than 5 years to 12% of its baseline level. This impact was not observed until the third year after vaccine introduction.

Burden of invasive disease caused by Haemophilus influenzae type b in Bamako, Mali: impetus for routine infant immunization with conjugate vaccine

BACKGROUND

Population-based, bacteriologically confirmed disease burden data aid decision makers in African countries pondering whether to introduce Haemophilus influenzae type b (Hib) immunization for infants.

METHODS

A bacteriology laboratory was established in Hopital Gabriel Toure, serving Bamako, Mali. Children age 0-15 years with fever > or =39 degrees C or syndromes compatible with invasive bacterial disease (meningitis, etc.) were eligible. From 2 to 5 mL of blood or relevant body fluid were inoculated into Bactec Ped Plus/F medium for automated culture; body fluids were also inoculated directly onto solid media. Hib was confirmed by standard microbiologic techniques and antibiograms generated by disk diffusion.

RESULTS

From June 1, 2002 to May 31, 2004, 3592 (87.8%) of 4092 children admitted to Hopital Gabriel Toure with high fever or suspected invasive bacterial disease were cultured, including 1745 who were 0-11 months old, 1132 who were 1-4 years old and 715 who were 5-15 years old. Hib was isolated from 207 Bamako children, 81 from blood alone and 124 from cerebrospinal fluid (with or without positive blood culture). Of 207 cases 204 (98.5%) occurred in children younger than age 5 years (annual incidence, 45.2/10) and 159 (77%) in infants age 0-11 months (annual incidence, 158.4/10). Peak incidence (370.0 cases/10) and 12 of 21 Hib deaths occurred in 6- to 7-month-olds. Of the Hib isolates, 11.1% were resistant to ampicillin, 32% to chloramphenicol and 0.5% to ceftriaxone.

CONCLUSIONS

The substantial burden of invasive Hib disease documented in Bamako has prompted the Malian government to introduce routine infant immunization with Hib conjugate.

The WHO Vaccine Trial Registry

The WHO Vaccine Trial Registry prospectively registers clinical vaccine studies supported by WHO. Through December 1999, the registry includes 103 studies from 43 countries, with nearly 80% in developing countries. The registry documents an expanding research capacity, with an average of 3.9 new studies per year during 1987-1993, rising to 10.7 per year during 1994-2000. The studies concern a broad spectrum of infectious organisms, including: Clostridium tetani (tetanus), dengue virus, enterotoxigenic Escherichia coli (ETEC), Haemophilus influenzae type b (Hib), hepatitis B virus, measles virus, Mycobacterium tuberculosis, Neisseria meningitidis (meningococcus), poliovirus, respiratory syncytial virus (RSV), rotavirus, Salmonella typhi, Shigella, Streptococcus pneumoniae (pneumococcus), and Vibrio cholerae.