Maternal Immunization With an Investigational Trivalent Group B Streptococcal Vaccine: A Randomized Controlled Trial

Re-framing the importance of Group B Streptococcus as a gut-resident pathobiont

Streptococcus agalactiae (Group B Streptococcus, GBS) is a Gram-positive bacterial species that causes disease in humans across the lifespan. While antibiotics are used to mitigate GBS infections, it is evident that antibiotics disrupt human microbiomes (which can predispose people to other diseases later in life), and antibiotic resistance in GBS is on the rise. Taken together, these unintended negative impacts of antibiotics highlight the need for precision approaches for minimizing GBS disease. One possible approach involves selectively depleting GBS in its commensal niches before it can cause disease at other body sites or be transmitted to at-risk individuals. One understudied commensal niche of GBS is the adult gastrointestinal (GI) tract, which may predispose colonization at other body sites in individuals at risk for GBS disease. However, a better understanding of the host-, microbiome-, and GBS-determined variables that dictate GBS GI carriage is needed before precise GI decolonization approaches can be developed. In this review, we synthesize current knowledge of the diverse body sites occupied by GBS as a pathogen and as a commensal. We summarize key molecular factors GBS utilizes to colonize different host-associated niches to inform future efforts to study GBS in the GI tract. We also discuss other GI commensals that are pathogenic in other body sites to emphasize the broader utility of precise de-colonization approaches for mitigating infections by GBS and other bacterial pathogens. Finally, we highlight how GBS treatments could be improved with a more holistic understanding of GBS enabled by continued GI-focused study.

Maternal GBS vaccination for preventing group B streptococcus disease in newborns: A mini review of current evidence

Group B streptococcus (GBS) poses a significant threat to neonates, leading to morbidity and mortality. Intrapartum antibiotics, although effective, have limitations, prompting the exploration of maternal vaccination. This study reviews the current evidence for maternal GBS vaccination in the prevention of early-onset GBS disease in newborns. A search on Google Scholar, PubMed, and Scopus identified studies assessing the impact of maternal GBS vaccination on early-onset GBS disease. Inclusion criteria comprised English-language clinical trials or observational studies. Data extraction included study details, immunogenicity profiles, effectiveness, safety outcomes, and relevant findings. Qualitative synthesis was employed for data analysis. Five studies meeting the inclusion criteria were reviewed. Maternal GBS vaccines demonstrated efficacy with sustained immunogenicity. Adverse events, although documented, were predominantly non-severe. Variability in immune responses and maternal-to-infant antibody ratios show the need for tailored vaccination approaches. Long-term follow up and surveillance are essential to assess persistence and identify unintended effects. Positive outcomes in vaccine efficacy support GBS vaccination integration into maternal health programs. Implementation challenges in diverse healthcare infrastructures require tailored approaches, especially in resource-limited settings. Overcoming cultural barriers and ensuring healthcare provider awareness are crucial for successful vaccination.

Defining and reporting adverse events of special interest in comparative maternal vaccine studies: a systematic review

Introduction

The GAIA (Global Alignment on Immunisation Safety Assessment in Pregnancy) consortium was established in 2014 with the aim of creating a standardised, globally coordinated approach to monitoring the safety of vaccines administered in pregnancy. The consortium developed twenty-six standardised definitions for classifying obstetric and infant adverse events. This systematic review sought to evaluate the current state of adverse event reporting in maternal vaccine trials following the publication of the case definitions by GAIA, and the extent to which these case definitions have been adopted in maternal vaccine safety research.

Methods

A comprehensive search of published literature was undertaken to identify maternal vaccine research studies. PubMed, EMBASE, Web of Science, and Cochrane were searched using a combination of MeSH terms and keyword searches to identify observational or interventional studies that examined vaccine safety in pregnant women with a comparator group. A two-reviewer screening process was undertaken, and a narrative synthesis of the results presented.

Results

14,737 titles were identified from database searches, 435 titles were selected as potentially relevant, 256 were excluded, the remaining 116 papers were included. Influenza vaccine was the most studied (25.0%), followed by TDaP (20.7%) and SARS-CoV-2 (12.9%).Ninety-one studies (78.4%) were conducted in high-income settings. Forty-eight (41.4%) utilised electronic health-records. The majority focused on reporting adverse events of special interest (AESI) in pregnancy (65.0%) alone or in addition to reactogenicity (27.6%). The most frequently reported AESI were preterm birth, small for gestational age and hypertensive disorders. Fewer than 10 studies reported use of GAIA definitions. Gestational age assessment was poorly described; of 39 studies reporting stillbirths 30.8% provided no description of the gestational age threshold.

Conclusions

Low-income settings remain under-represented in comparative maternal vaccine safety research. There has been poor uptake of GAIA case definitions. A lack of harmonisation and standardisation persists limiting comparability of the generated safety data.

Using Surface Immunogenic Protein as a Carrier Protein to Elicit Protective Antibody to Multiple Serotypes for Candidate Group B Streptococcal Glycan Conjugate Vaccines

Group B Streptococcus (GBS) is a life-threatening opportunistic pathogen, particularly in pregnant women, infants, and the elderly. Currently, maternal vaccination is considered the most viable long-term option for preventing GBS mother-to-infant infection, and two polysaccharide conjugate vaccines utilizing CRM197 as a carrier protein have undergone clinical phase II trials. Surface immunogenic protein (Sip), present in all identified serotypes of GBS strains so far, is a protective surface protein of GBS. In this study, the type Ia capsular polysaccharide (CPS) of GBS was utilized as a model to develop candidate antigens for a polysaccharide conjugate vaccine by coupling it with the Sip of GBS and the traditional carrier protein CRM197. Serum analysis from immunized New Zealand rabbits and CD1 mice revealed that there was no significant difference in antibody titers between the Ia-Sip group and Ia-CRM197 group; however, both were significantly higher than those observed in the Ia polysaccharide group. Opsonophagocytosis and passive immune protection results using rabbit serum indicated no significant difference between the Ia-Sip and Ia-CRM197 groups, both outperforming the Ia polysaccharide group. Furthermore, serum from the Ia-Sip group had a cross-protective effect on multiple types of GBS strains. The challenge test results in CD1 mice demonstrated that the Ia-Sip group provided complete protection against lethal doses of bacteria and also showed cross-protection against type III strain. Our study demonstrates for the first time that Ia-Sip is immunogenic and provides serotype-independent protection in glycan conjugate vaccines, which also indicates Sip may serve as an excellent carrier protein for GBS glycan conjugate vaccines and provide cross-protection against multiple GBS strains.

A Review of the Impact of Streptococcal Infections and Antimicrobial Resistance on Human Health

Streptococcus pneumoniae, Streptococcus pyogenes (GAS), and Streptococcus agalactiae (GBS) are bacteria that can cause a range of infections, some of them life-threatening. This review examines the spread of antibiotic resistance and its mechanisms against antibiotics for streptococcal infections. Data on high-level penicillin-resistant invasive pneumococci have been found in Brazil (42.8%) and Japan (77%). The resistance is caused by mutations in genes that encode penicillin-binding proteins. Similarly, GAS and GBS strains reported from Asia, the USA, and Africa have undergone similar transformations in PBPs. Resistance to major alternatives of penicillins, macrolides, and lincosamides has become widespread among pneumococci and streptococci, especially in Asia (70-95%). The combination of several emm types with erm(B) is associated with the development of high-level macrolide resistance in GAS. Major mechanisms are ribosomal target modifications encoded by erm genes, ribosomal alterations, and active efflux pumps that regulate antibiotic entry due to mefA/E and msrD genes. Tetracycline resistance for streptococci in different countries varied from 22.4% in the USA to 83.7/100% in China, due to tet genes. Combined tetracycline/macrolide resistance is usually linked with the insertion of ermB into the transposon carrying tetM. New quinolone resistance is increasing by between 11.5 and 47.9% in Asia and Europe. The mechanism of quinolone resistance is based on mutations in gyrA/B, determinants for DNA gyrase, or parC/E encoding topoisomerase IV. The results for antibiotic resistance are alarming, and urgently call for increased monitoring of this problem and precautionary measures for control to prevent the spread of resistant mutant strains.

An Overview of Antibiotic Therapy for Early- and Late-Onset Neonatal Sepsis: Current Strategies and Future Prospects

Neonatal sepsis is a clinical syndrome mainly associated with a bacterial infection leading to severe clinical manifestations that could be associated with fatal sequalae. According to the time of onset, neonatal sepsis is categorized as early- (EOS) or late-onset sepsis (LOS). Despite blood culture being the gold standard for diagnosis, it has several limitations, and early diagnosis is not immediate. Consequently, most infants who start empirical antimicrobial therapy do not have an underlying infection. Despite stewardship programs partially reduced this negative trend, in neonatology, antibiotic overuse still persists, and it is associated with several relevant problems, the first of which is the increase in antimicrobial resistance (AMR). Starting with these considerations, we performed a narrative review to summarize the main findings and the future prospects regarding antibiotics use to treat neonatal sepsis. Because of the impact on morbidity and mortality that EOS and LOS entail, it is essential to start an effective and prompt treatment as soon as possible. The use of targeted antibiotics is peremptory as soon as the pathogen in the culture is detected. Although prompt therapy is essential, it should be better assessed whether, when and how to treat neonates with antibiotics, even those at higher risk. Considering that we are certainly in the worrying era defined as the "post-antibiotic era", it is still essential and urgent to define novel strategies for the development of antibacterial compounds with new targets or mechanisms of action. A future strategy could also be to perform well-designed studies to develop innovative algorithms for improving the etiological diagnosis of infection, allowing for more personalized use of the antibiotics to treat EOS and LOS.

Prenatal Maternal Immunization for Infant Protection: A Review of the Vaccines Recommended, Infant Immunity and Future Research Directions

Prenatal maternal immunization is an effective tool to protect mothers and infants from poor health outcomes due to infectious diseases. We provide an overview of the rationale for the use of prenatal vaccines, discuss the immunologic environment of the maternal-fetal interface including the impact of maternal vaccines prenatally and subsequently on the infant's immune response, and review vaccines currently recommended in pregnancy and landscape for the future of maternal vaccination. This review aims to provide an understanding of the recent history and progress made in the field and highlight the importance of continued research and development into new vaccines for pregnant populations.

The immunogenicity and safety of Group B Streptococcal maternal vaccines: A systematic review

PURPOSE

To systematically review immunogenicity and safety data of maternal group B streptococcal (GBS) vaccines in published clinical trials until July 2023.

METHODS

EMBASE, MEDLINE, Cochrane Library and clinicaltrial.gov. databases were searched for clinical studies that reported immunogenicity and/or safety of GBS vaccine in non-pregnant adults, pregnant women and infants between 1st of January 1996 to 31st of July 2023. Pairs of reviewers independently selected, data extracted, and assessed the risk of bias of the studies. Discrepancies were resolved by consensus. (PROSPERO CRD42020185213).

RESULTS

We retrieved 1472 records from the literature search; 20 studies and 6 sub-studies were included, involving 4440 non-pregnant participants and 1325 pregnant women with their newborns. There was a significantly higher IgG Geometric Mean Concentration (GMC) and IgG placental transfer ratios in vaccinated compared to placebo groups, with peak response 4-8 weeks after vaccination. Placental transfer ratio varied from 0.4 to 1.4 across five studies. The different clinical trials used different assays that limited direct comparison. There were no significant differences in the risk of serious adverse events (adjusted OR 0.73; 95 % CI 0.49-1.07), serious adverse events leading to withdrawal (adjusted OR 0.44; 95 % CI 0.13-1.51), and systemic illness or fever (adjusted OR 1.05; 95 % CI 0.26-4.19) between the vaccine and placebo groups.

CONCLUSIONS

The published clinical trials show significant IgG GMC response in subjects receiving the conjugated capsular polysaccharide and surface subunit protein vaccines compared to placebo. In current clinical trials of experimental GBS maternal vaccines, there have been no observed serious adverse events of special interest directly linked to vaccination.

Epidemiologic Changes of Neonatal Early-onset Sepsis After the Implementation of Universal Maternal Screening for Group B Streptococcus in Hong Kong

BACKGROUND

The epidemiology of neonatal early-onset sepsis (EOS) has changed with time and with changes in prevention strategy. Population-representative contemporary data provide insights on how to further improve EOS prevention and triage strategies.

METHODS

Neonates born in public hospitals in Hong Kong from January 1, 2006, to December 31, 2017 were included. The epidemiological characteristics of EOS and the use of intrapartum antibiotic prophylaxis (IAP) were compared between the 2 epochs before (January 1, 2006 to December 31, 2011) and after (January 1, 2012 to December 31, 2017) the territory-wide implementation of universal maternal group B Streptococcus (GBS) screening.

RESULTS

EOS developed in 1.07‰ of live births (522/490,034). After the implementation of universal GBS screening, the EOS rate decreased in neonates born ≥34 weeks (1.17‰-0.56‰, P < 0.001) and remained similar in those born <34 weeks (7.8‰-10.9‰, P = 0.15), whereas the proportions of IAP coverage increased in both groups [7.6%-23.3% ( P < 0.001) and 28.5%-52.0% ( P < 0.001), respectively]. The major pathogen for EOS shifted from GBS to Escherichia coli , and for early-onset meningitis from GBS to Streptococcus bovis . IAP was associated with subsequent isolation of pathogens resistant to ampicillin [adjusted odds ratio (aOR) 2.3; 95% confidence interval (CI): 1.3-4.2], and second-generation [aOR 2.0; 95% CI: 1.02-4.3] and third-generation [aOR 2.2; 95% CI: 1.1-5.0] cephalosporins.

CONCLUSIONS

Pathogen profile of EOS changed with the implementation of universal GBS screening. S. bovis has emerged as a more common pathogen associated with the risk of meningitis. IAP may not be as effective in reducing EOS rate among infants born <34 weeks as compared with those ≥34 weeks, and newer strategies may be needed.

Potential for Maternally Administered Vaccine for Infant Group B Streptococcus

BACKGROUND

Natural history studies have correlated serotype-specific anti-capsular polysaccharide (CPS) IgG in newborns with a reduced risk of group B streptococcal disease. A hexavalent CPS-cross-reactive material 197 glycoconjugate vaccine (GBS6) is being developed as a maternal vaccine to prevent invasive group B streptococcus in young infants.

METHODS

In an ongoing phase 2, placebo-controlled trial involving pregnant women, we assessed the safety and immunogenicity of a single dose of various GBS6 formulations and analyzed maternally transferred anti-CPS antibodies. In a parallel seroepidemiologic study that was conducted in the same population, we assessed serotype-specific anti-CPS IgG concentrations that were associated with a reduced risk of invasive disease among newborns through 89 days of age to define putative protective thresholds.

RESULTS

Naturally acquired anti-CPS IgG concentrations were associated with a reduced risk of disease among infants in the seroepidemiologic study. IgG thresholds that were determined to be associated with 75 to 95% reductions in the risk of disease were 0.184 to 0.827 μg per milliliter. No GBS6-associated safety signals were observed among the mothers or infants. The incidence of adverse events and of serious adverse events were similar across the trial groups for both mothers and infants; more local reactions were observed in the groups that received GBS6 containing aluminum phosphate. Among the infants, the most common serious adverse events were minor congenital anomalies (umbilical hernia and congenital dermal melanocytosis). GBS6 induced maternal antibody responses to all serotypes, with maternal-to-infant antibody ratios of approximately 0.4 to 1.3, depending on the dose. The percentage of infants with anti-CPS IgG concentrations above 0.184 μg per milliliter varied according to serotype and formulation, with 57 to 97% of the infants having a seroresponse to the most immunogenic formulation.

CONCLUSIONS

GBS6 elicited anti-CPS antibodies against group B streptococcus in pregnant women that were transferred to infants at levels associated with a reduced risk of invasive group B streptococcal disease. (Funded by Pfizer and the Bill and Melinda Gates Foundation; C1091002 ClinicalTrials.gov number, NCT03765073.).

Early-onset group B streptococcal disease in African countries and maternal vaccination strategies

Invasive group B streptococcal (GBS) disease is the commonest perinatally-acquired bacterial infection in newborns; the burden is higher in African countries where intrapartum antibiotic prophylaxis strategies are not feasible. In sub-Saharan Africa, almost one in four newborns with GBS early-onset disease will demise, and one in ten survivors have moderate or severe neurodevelopmental impairment. A maternal GBS vaccine to prevent invasive GBS disease in infancy is a pragmatic and cost-effective preventative strategy for Africa. Hexavalent polysaccharide protein conjugate and Alpha family surface protein vaccines are undergoing phase II clinical trials. Vaccine licensure may be facilitated by demonstrating safety and immunological correlates/thresholds suggestive of protection against invasive GBS disease. This will then be followed by phase IV effectiveness studies to assess the burden of GBS vaccine preventable disease, including the effect on all-cause neonatal infections, neonatal deaths and stillbirths.

Adverse infant outcomes following low-risk pregnancies in England: a retrospective cohort study

BACKGROUND

There are limited data describing adverse infant outcomes in infants born to women with a low risk of complications during pregnancy, such as those who may be enrolled in maternal immunization trials. This retrospective study estimated incidence proportions of infant outcomes in different cohorts of liveborn infants in England between 2005 and 2017.

METHODS

The incidence proportions of 10 infant outcomes were calculated for liveborn infants from pregnancies represented in the Clinical Practice Research Datalink (CPRD) Mother-Baby Link (MBL) and linkage to Hospital Episode Statistics (HES). Three infant cohorts were designed: (1) the all pregnancies infants cohort (N = 185,119), (2) the all pregnancies with a gestational age (GA) ≥ 24 weeks infants cohort (N = 183,869), and (3) the low-risk pregnancies infants cohort (LR infants cohort, N = 121,871), which included pregnancies with a GA ≥ 24 weeks and no diagnosis of predefined high-risk medical conditions until 24 weeks GA.

RESULTS

The most common adverse infant outcome in the three infant cohorts was macrosomia (e.g., 1,085.9/10,000 live births in the LR infants cohort), followed by minor congenital anomalies (e.g., 800.6/10,000 in the LR infants cohort), very low/low birth weight (e.g., 400.6/10,000 in the LR infants cohort), and major congenital anomalies (e.g., 270.4/10,000 in the LR infants cohort). The incidence proportions for early-onset sepsis, very low/low birth weight, and minor and major congenital anomalies were lower in the LR infants than in the other cohorts (non-overlapping confidence intervals [CIs]). The incidence proportions of neonatal death, infant death, late-onset sepsis, macrosomia, small for GA, and large for GA were similar between cohorts (overlapping CIs).

CONCLUSIONS

This study generated background rates of adverse infant outcomes from liveborn infants of all and low-risk pregnancies represented in the CPRD Pregnancy Register MBL and linkage to HES. The results indicate lower incidence proportions of several adverse infant outcomes in infants from low-risk pregnancies compared to all pregnancies, illustrating the importance of considering maternal risk factors. These background rates may facilitate the interpretation of safety data from maternal immunization trials and of pharmacovigilance data from maternal vaccines. They may also be of interest for other interventions studied in pregnant women.

Safety and immunogenicity of the group B streptococcus vaccine AlpN in a placebo-controlled double-blind phase 1 trial

Group B streptococcus (GBS) is a leading cause of life-threatening neonatal infections and subsets of adverse pregnancy outcomes. Essentially all GBS strains possess one allele of the alpha-like protein (Alp) family. A maternal GBS vaccine, consisting of the fused N-terminal domains of the Alps αC and Rib (GBS-NN), was recently demonstrated to be safe and immunogenic in healthy adult women. To enhance antibody responses to all clinically relevant Alps, a second-generation vaccine has been developed (AlpN), also containing the N-terminal domain of Alp1 and the one shared by Alp2 and Alp3. In this study, the safety and immunogenicity of AlpN is assessed in a randomized, double-blind, placebo-controlled, and parallel-group phase I study, involving 60 healthy non-pregnant women. AlpN is well tolerated and elicits similarly robust and persistent antibody responses against all four Alp-N-terminal domains, resulting in enhanced opsonophagocytic killing of all Alp serotypes covered by the vaccine.

Strategies to Prevent Early and Late-Onset Group B Streptococcal Infection via Interventions in Pregnancy

Group B Streptococcus is a Gram-positive bacterium that typically colonizes 10-30% of pregnant women, causing chorioamnionitis, preterm birth, and stillbirth, as well as neonatal sepsis and meningitis with early-onset disease (EOD) or late-onset disease (LOD) due to ascending infection or transmission during delivery. While there are some differences between EOD and LOD in terms of route of transmission, risk factors, and serotypes, the only preventive approach currently is maternal intrapartum antibiotic prophylaxis (IAP) which will not be able to fully address the burden of the disease since this has no impact on LOD. Probiotics and immunization in pregnancy may be more effective than IAP for both EOD and LOD. There is mixed evidence of probiotic effects on the prevention of GBS colonization, and the data from completed and ongoing clinical trials investigating different GBS vaccines are promising. Current vaccine candidates target bacterial proteins or the polysaccharide capsule and include trivalent, tetravalent, and hexavalent protein-polysaccharide conjugate vaccines. Some challenges in developing novel GBS vaccines include the lack of a correlate of protection, the potential for serotype switching, a need to understand interactions with other vaccines, and optimal timing of administration in pregnancy to maximize protection for both term and preterm infants.

Advances towards licensure of a maternal vaccine for the prevention of invasive group B streptococcus disease in infants: a discussion of different approaches

Group B streptococcus (Streptococcus agalactiae, GBS) is an important cause of life-threatening disease in newborns. Pregnant women colonized with GBS can transmit the bacteria to the developing fetus, as well as to their neonates during or after delivery where infection can lead to sepsis, meningitis, pneumonia, or/and death. While intrapartum antibiotic prophylaxis (IAP) is the standard of care for prevention of invasive GBS disease in some countries, even in such settings a substantial residual burden of disease remains. A GBS vaccine administered during pregnancy could potentially address this important unmet medical need and provide an adjunct or alternative to IAP for the prevention of invasive GBS disease in neonates. A hurdle for vaccine development has been relatively low disease rates making efficacy studies difficult. Given the well-accepted inverse relationship between anti-GBS capsular polysaccharide antibody titers at birth and risk of disease, licensure using serological criteria as a surrogate biomarker represents a promising approach to accelerate the availability of a GBS vaccine.

Transmission of Group B Streptococcus in late-onset neonatal disease: a narrative review of current evidence

Group B streptococcus (GBS) late-onset disease (LOD, occurring from 7 through 89 days of life) is an important cause of sepsis and meningitis in infants. The pathogenesis and modes of transmission of LOD to neonates are yet to be elucidated. Established risk factors for the incidence of LOD include maternal GBS colonisation, young maternal age, preterm birth, HIV exposure and African ethnicity. The mucosal colonisation by GBS may be acquired perinatally or in the postpartum period from maternal or other sources. Growing evidence has demonstrated the predominant role of maternal sources in the transmission of LOD. Intrapartum antibiotic prophylaxis (IAP) to prevent early-onset disease reduces neonatal GBS colonisation during delivery; however, a significant proportion of IAP-exposed neonates born to GBS-carrier mothers acquire the pathogen at mucosal sites in the first weeks of life. GBS-infected breast milk, with or without presence of mastitis, is considered a potential vehicle for transmitting GBS. Furthermore, horizontal transmission is possible from nosocomial and other community sources. Although unfrequently reported, nosocomial transmission of GBS in the neonatal intensive care unit is probably less rare than is usually believed. GBS disease can sometime recur and is usually caused by the same GBS serotype that caused the primary infection. This review aims to discuss the dynamics of transmission of GBS in the neonatal LOD.

Group B Streptococcus and Pregnancy: Critical Concepts and Management Nuances

Importance

Group B Streptococcus (GBS) is a common pathogen with an effective treatment. However, it remains a significant cause of neonatal sepsis, morbidity, and mortality. The screening and management of this infection are some of the first concepts learned during medical training in obstetrics. However, effective screening and evidence-based management of GBS are nuanced with many critical caveats.

Objective

The objectives of this review are to discuss the essential aspects of GBS screening and management and to highlight recent changes to recommendations and guidelines.

Evidence Acquisition

Original research articles, review articles, and guidelines on GBS were reviewed.

Results

The following recommendations are based on review of the evidence and professional society guidelines. Screening for GBS should occur between 36 weeks and the end of the 37th week. The culture swab should go 2 cm into the vagina and 1 cm into the anus. Patients can perform their own swabs as well. Penicillin allergy testing has been shown to be safe in pregnancy. Patients with GBS in the urine should be treated at term with antibiotic prophylaxis, independent of the colony count of the culture. Patients who are GBS-positive with preterm and prelabor rupture of membranes after 34 weeks are not candidates for expectant management, as this population has higher rates of neonatal infectious complications. Patients with a history of GBS colonization in prior pregnancy who are GBS-unknown in this current pregnancy and present with labor should receive intrapartum prophylaxis. Work on the GBS vaccine continues.

Conclusions

Although all of the efforts and focus on neonatal early-onset GBS infection have led to lower rates of disease, GBS still remains a major cause of neonatal morbidity and mortality requiring continued vigilance from obstetric providers.

Facilitating safety evaluation in maternal immunization trials: a retrospective cohort study to assess pregnancy outcomes and events of interest in low-risk pregnancies in England

BACKGROUND

Maternal characteristics like medical history and health-related risk factors can influence the incidence of pregnancy outcomes and pregnancy-related events of interest (EIs). Data on the incidence of these endpoints in low-risk pregnant women are needed for appropriate external safety comparisons in maternal immunization trials. To address this need, this study estimated the incidence proportions of pregnancy outcomes and pregnancy-related EIs in different pregnancy cohorts (including low-risk pregnancies) in England, contained in the Clinical Practice Research Datalink (CPRD) Pregnancy Register linked to Hospital Episode Statistics (HES) between 2005 and 2017.

METHODS

The incidence proportions of 7 pregnancy outcomes and 15 EIs were calculated for: (1) all pregnancies (AP) represented in the CPRD Pregnancy Register linked to HES (AP cohort; N = 298 155), (2) all pregnancies with a gestational age (GA) ≥ 24 weeks (AP24+ cohort; N = 208 328), and (3) low-risk pregnancies (LR cohort; N = 137 932) with a GA ≥ 24 weeks and no diagnosis of predefined high-risk medical conditions until 24 weeks GA.

RESULTS

Miscarriage was the most common adverse pregnancy outcome in the AP cohort (1 379.5 per 10 000 pregnancies) but could not be assessed in the other cohorts because these only included pregnancies with a GA ≥ 24 weeks, and miscarriages with GA ≥ 24 weeks were reclassified as stillbirths. Preterm delivery (< 37 weeks GA) was the most common adverse pregnancy outcome in the AP24+ and LR cohorts (742.9 and 680.0 per 10 000 pregnancies, respectively). Focusing on the cohorts with a GA ≥ 24 weeks, the most common pregnancy-related EIs in the AP24+ and LR cohorts were fetal/perinatal distress or asphyxia (1 824.3 and 1 833.0 per 10 000 pregnancies), vaginal/intrauterine hemorrhage (799.2 and 729.0 per 10 000 pregnancies), and labor protraction/arrest disorders (752.4 and 774.5 per 10 000 pregnancies).

CONCLUSIONS

This study generated incidence proportions of pregnancy outcomes and pregnancy-related EIs from the CPRD for different pregnancy cohorts, including low-risk pregnancies. The reported incidence proportions of pregnancy outcomes and pregnancy-related EIs are largely consistent with external estimates. These results may facilitate the interpretation of safety data from maternal immunization trials and the safety monitoring of maternal vaccines. They may also be of interest for any intervention studied in populations of pregnant women.

A Recombinant Alpha-Like Protein Subunit Vaccine (GBS-NN) Provides Protection in Murine Models of Group B Streptococcus Infection

BACKGROUND

Group B Streptococcus (GBS) transmission during pregnancy causes preterm labor, stillbirths, fetal injury, or neonatal infections. Rates of adult infections are also rising. The GBS-NN vaccine, engineered by fusing N-terminal domains of GBS Alpha C and Rib proteins, is safe in healthy, nonpregnant women, but further assessment is needed for use during pregnancy. Here, we tested GBS-NN vaccine efficacy using mouse models that recapitulate human GBS infection outcomes.

METHODS

Following administration of GBS-NN vaccine or adjuvant, antibody profiles were compared by ELISA. Vaccine efficacy was examined by comparing infection outcomes in GBS-NN vaccinated versus adjuvant controls during systemic and pregnancy-associated infections, and during intranasal infection of neonatal mice following maternal vaccination.

RESULTS

Vaccinated mice had higher GBS-NN-specific IgG titers versus controls. These antibodies bound alpha C and Rib on GBS clinical isolates. Fewer GBS were recovered from systemically challenged vaccinated mice versus controls. Although vaccination did not eliminate GBS during ascending infection in pregnancy, vaccinated dams experienced fewer in utero fetal deaths. Additionally, maternal vaccination prolonged neonatal survival following intranasal GBS challenge.

CONCLUSIONS

These findings demonstrate GBS-NN vaccine efficacy in murine systemic and perinatal GBS infections and suggest that maternal vaccination facilitates the transfer of protective antibodies to neonates.

Is Group B Streptococcus Colonization Associated with Maternal Peripartum Infection in an Era of Routine Prophylaxis?

OBJECTIVE

This study aimed to assess whether colonization with group B streptococcus (GBS) is associated with maternal peripartum infection in an era of routine prophylaxis.

STUDY DESIGN

This study presented a secondary analysis of women delivering ≥37 weeks who underwent a trial of labor from the U.S. Consortium on Safe Labor (CSL) study. The exposure was maternal GBS colonization and the outcome was a diagnosis of chorioamnionitis, and secondarily, analyses were restricted to deliveries not admitted in labor and measures of postpartum infection (postpartum fever, endometritis, and surgical site infection). Logistic regression with generalized estimating equations was used accounting for within-woman correlations. Models adjusted for maternal age, parity, race, prepregnancy body mass index, pregestational diabetes, insurance status, study site/region, year of delivery, number of vaginal exams from admission to delivery, and time (in hours) from admission to delivery.

RESULTS

Among 170,804 assessed women, 33,877 (19.8%) were colonized with GBS and 5,172 (3.0%) were diagnosed with chorioamnionitis. While the frequency of GBS colonization did not vary by chorioamnionitis status (3.0% in both groups), in multivariable analyses, GBS colonization was associated with slightly lower odds of chorioamnionitis (adjusted odds ratio [AOR]: 0.89; 95% confidence interval [CI]: 0.83-0.96). In secondary analyses, this association held regardless of spontaneous labor on admission; and the odds of postpartum infectious outcomes were not higher with GBS colonization.

CONCLUSION

In contrast to historical data, GBS colonization was associated with lower odds of chorioamnionitis in an era of routine GBS screening and prophylaxis.

KEY POINTS

· Data in an era prior to routine group B streptococcus (GBS) screening and prophylaxis showed that maternal GBS colonization was associated with a higher frequency of maternal peripartum infection.. · In the current study, GBS colonization was associated with lower odds of chorioamnionitis in an era of routine GBS screening and prophylaxis.. · The results highlight potential benefits of GBS screening and intrapartum antibiotic prophylaxis beyond neonatal disease prevention, including mitigating the risk of maternal infectious morbidity..

Safety and immunogenicity of a prototype recombinant alpha-like protein subunit vaccine (GBS-NN) against Group B Streptococcus in a randomised placebo-controlled double-blind phase 1 trial in healthy adult women

BACKGROUND

Group B Streptococcus (GBS) is the leading cause of life-threatening infections in new-borns and may cause invasive disease, stillbirth and preterm delivery during pregnancy. While no licensed vaccine exists, maternal immunization might protect against neonatal disease and adverse pregnancy outcomes. We assessed the safety and immunogenicity of a prototype vaccine consisting of the fused N-terminal domains of the AlphaC and Rib surface proteins of GBS (GBS-NN).

METHODS

GBS-NN was tested in a randomised, double-blind, placebo-controlled, parallel group, phase I study, in healthy non-pregnant women. A dose-escalation phase, with two doses, four weeks apart, of 10, 50 or 250 µg, administered with or without aluminium hydroxide, was initially assessed (n = 60). This was followed by a dose-confirmation study, where one dose of 100 µg adjuvanted GBS-NN was compared with two doses of either 50 or 100 µg adjuvanted GBS-NN, again administered with four weeks interval between the doses (n = 180). Safety and immunogenicity were monitored for one year.

RESULTS

GBS-NN was well tolerated with some, mostly mild, injection site reactions observed. Adjuvant significantly increased antibody concentrations and the response was boosted by a second dose. The IgG GMCs remained strongly elevated during the whole one-year duration of the study. Maximal responses occurred after two 50 µg doses, resulting in IgG GMC of 16.9 µg/ml at the primary immunological endpoint, twelve weeks after the first dose. For this regimen, 100% and 89% of the subjects achieved antibody levels above the arbitrary thresholds of 1 and 4 µg/ml, respectively. The added beneficial effect of a second dose was most pronounced for subjects with pre-existing IgG levels below the median of the entire cohort.

CONCLUSION

The prototype GBS-NN vaccine was found to be well tolerated and highly immunogenic with an optimal regimen of two doses of 50 µg in the presence of adjuvant. Further development of a maternal vaccine based on the N-terminal domains of the alpha-like protein family of GBS is warranted (NCT02459262).

Cost-effectiveness of maternal immunization against neonatal invasive Group B Streptococcus in the Netherlands

BACKGROUND

Neonatal invasive Group B Streptococcus (GBS) infection causes considerable disease burden in the Netherlands. Intrapartum antibiotic prophylaxis (IAP) prevents early-onset disease (EOD), but has no effect on late-onset disease (LOD). A potential maternal GBS vaccine could prevent both EOD and LOD by conferring immunity in neonates.

OBJECTIVE

Explore under which circumstances maternal vaccination against GBS would be cost-effective as an addition to, or replacement for the current risk factor-based IAP prevention strategy in the Netherlands.

METHODS

We assessed the maximum cost-effective price per dose of a trivalent (serotypes Ia, Ib, and III) and hexavalent (additional serotypes II, IV, and V) GBS vaccine in addition to, or as a replacement for IAP. To project the prevented costs and disease burden, a decision tree model was developed to reflect neonatal GBS disease and long-term health outcomes among a cohort based on 169,836 live births in the Netherlands in 2017.

RESULTS

Under base-case conditions, maternal immunization with a trivalent vaccine would gain 186 QALYs and prevent more than €3.1 million in health care costs when implemented in addition to IAP. Immunization implemented as a replacement for IAP would gain 88 QALYs compared to the current prevention strategy, prevent €1.5 million in health care costs, and avoid potentially ~ 30,000 IAP administrations. The base-case results correspond to a maximum price of €58 per dose (vaccine + administration costs; using a threshold of €20,000/QALY). Expanding the serotype coverage to a hexavalent vaccine would only have a limited additional impact on the cost-effectiveness in the Netherlands.

CONCLUSIONS

A maternal GBS vaccine could be cost-effective when implemented in addition to the current risk factor-based IAP prevention strategy in the Netherlands. Discontinuation of IAP would save costs and prevent antibiotic use, however, is projected to lead to a lower health gain compared to vaccination in addition to IAP.

Safety and Immunogenicity of a Second Dose of an Investigational Maternal Trivalent Group B Streptococcus Vaccine in Nonpregnant Women 4-6 Years After a First Dose: Results From a Phase 2 Trial

Background

Maternal immunization against group B streptococcus (GBS) could protect infants from invasive GBS disease. Additional doses in subsequent pregnancies may be needed. We evaluated the safety and immunogenicity of a second dose of an investigational trivalent CRM₁₉₇-glycoconjugate GBS vaccine (targeting serotypes Ia/Ib/III), administered to nonpregnant women 4–6 years postdose 1.

Methods

Healthy women either previously vaccinated with 1 dose of trivalent GBS vaccine 4–6 years before enrollment (n = 53) or never GBS vaccinated (n = 27) received a single trivalent GBS vaccine injection. Adverse events (AEs) were recorded. Serotype-specific (Ia/Ib/III) anti-GBS antibodies were measured by multiplex immunoassay prevaccination and 30/60 days postvaccination.

Results

AEs were reported with similar rates after a first or second dose; none were serious. Of previously GBS-vaccinated women, 92%–98% had anti-GBS concentrations that exceeded an arbitrary threshold (8 µg/mL) for each serotype 60 days postdose 2 vs 36%–56% postdose 1 in previously non–GBS-vaccinated women. Of previously GBS-vaccinated women with undetectable baseline (predose 1) anti-GBS levels, 90%–98% reached this threshold postdose 2. For each serotype, anti-GBS geometric mean concentrations (GMCs) 30/60 days postdose 2 in previously GBS-vaccinated women were ≥200-fold higher than baseline GMCs. Among women with undetectable baseline anti-GBS levels, postdose 2 GMCs in previously GBS-vaccinated women exceeded postdose 1 GMCs in previously non–GBS-vaccinated women (≥7-fold).

Conclusions

A second trivalent GBS vaccine dose administered 4–6 years postdose 1 was immunogenic with a favorable safety profile. Women with undetectable preexisting anti-GBS concentrations may benefit from a sufficiently spaced second vaccine dose.

Clinical Trials Registration

NCT02690181

Association of Group B streptococcus serum serotype-specific anti-capsular IgG concentration and risk reduction for invasive Group B streptococcus disease in South African infants: an observational birth-cohort, matched case-control study

BACKGROUND

Licensure of a Group B streptococcus (GBS) polysaccharide-protein conjugate vaccine for protecting infants against invasive GBS disease (IGbsD) will likely need to be based on demonstrating vaccine safety in pregnant women, and benchmarking immunogenicity against a serological threshold associated with risk reduction of IGbsD. We investigated the association between naturally-derived GBS serotype-Ia and III IgG and risk reduction of IGbsD in infants' ≤90 days of age.

METHODS

In a matched case-control study (ClinicalTrials.gov NCT02215226), IGbsD cases were identified from a cohort of 38,233 mother-newborn dyads. Mothers colonized vaginally with serotype-Ia or III at birth, and their healthy infants were eligible as matched controls. GBS serotype-specific anti-capsular IgG was measured on maternal and cord blood/infant sera by multiplex Luminex assay; and the IgG threshold associated with 90% risk reduction of IGbsD derived by estimating absolute disease risk.

RESULTS

In infants born ≥34 weeks gestational age, cord-blood IgG geometric mean concentrations (GMC) were lower in cases than controls for serotype-Ia (0.05 vs. 0.50µg/ml; p=0.004) and III (0.20 vs. 0.38µg/ml; p=0.078). Cord-blood IgG concentration ≥1.04 and ≥1.53µg/ml were associated with 90% risk reduction of serotype-Ia and III IGbsD, respectively. The maternal sera IgG threshold associated with 90% risk reduction was ≥2.31 and ≥3.41µg/ml for serotype-Ia and III, respectively.

CONCLUSIONS

The threshold associated with a reduced risk for serotype-Ia and III IGbsD identified on infant sera supports the case for licensure of a GBS polysaccharide-protein conjugate vaccine based on immunogenicity evaluation benchmarked against the defined thresholds.

Structure-based glycoconjugate vaccine design: The example of Group B Streptococcus type III capsular polysaccharide

Microbial surface polysaccharides are important virulence factors and targets for vaccine development. Glycoconjugate vaccines, obtained by covalently linking carbohydrates and proteins, are well established tools for prevention of bacterial infections. Elucidation of the minimal portion involved in the interactions with functional antibodies is of utmost importance for the understanding of their mechanism of induction of protective immune responses and the design of synthetic glycan based vaccines. Typically, this is achieved by combination of different techniques, which include ELISA, glycoarray, Surface Plasmon Resonance in conjunction with approaches for mapping at atomic level the position involved in binding, such as Saturation Transfer NMR and X-ray crystallography. This review provides an overview of the structural studies performed to map glycan epitopes (glycotopes), with focus on the highly complex structure of Group B Streptococcus type III (GBSIII) capsular polysaccharide. Furthermore, it describes the rational process followed to translate the obtained information into the design of a protective glycoconjugate vaccine based on a well-defined synthetic glycan epitope.

Safety and immunogenicity of an investigational maternal trivalent group B streptococcus vaccine in pregnant women and their infants: Results from a randomized placebo-controlled phase II trial

BACKGROUND

This study evaluated the safety and immunogenicity of an investigational trivalent group B streptococcus (GBS) vaccine in US pregnant women, transplacental serotype-specific antibody transfer and persistence in infants, and serotype-specific antibodies in breast milk.

METHODS

This randomized, observer-blind, placebo-controlled trial administered one dose of trivalent GBS vaccine (n = 49) or placebo (n = 26) to healthy pregnant 18-40-year-old women at 24^0/7-34^6/7 weeks' gestation. Women were enrolled from March 2014 to August 2015. Safety follow-up continued through postpartum day 180. Primary immunogenicity objectives were to evaluate serotype Ia/Ib/III-specific immunoglobulin G (IgG) levels in sera from women on day 1 (pre-vaccination), day 31, delivery and postpartum days 42 and 90, and from infants at birth (cord blood), days 42 and 90. Antibody transfer ratios (cord blood/maternal sera at delivery) and serotype-specific secretory immunoglobulin A (sIgA) and IgG in breast milk after delivery and on postpartum days 42 and 90 were evaluated. The planned sample size was not based on statistical assumptions for this descriptive study.

RESULTS

Baseline characteristics were similar between groups. Serious adverse events were reported for 16% of GBS-vaccinated women and 15% of their infants, and 15% of placebo recipients and 12% of their infants; none were fatal or deemed vaccine-related. Serotype-specific IgG geometric mean concentrations (GMCs) were 13-23-fold higher in vaccine vs placebo recipients on day 31 and persisted until postpartum day 90. Median antibody concentrations were substantially higher in women with detectable pre-vaccination antibody concentrations. Antibody transfer ratios in the vaccine group were 0.62-0.82. Infant IgG GMCs and breast milk sIgA GMCs were higher in the vaccine vs the placebo group at all timepoints.

CONCLUSIONS

Maternal immunization with the trivalent GBS vaccine in US women had a favorable safety profile, elicited antibodies that were transplacentally transferred and persisted in infants for a minimum of 3 months.

CLINICAL TRIAL REGISTRATION

Clinicaltrials.gov, NCT02046148.

A Phase 2, Randomized, Control Trial of Group B Streptococcus (GBS) Type III Capsular Polysaccharide-tetanus Toxoid (GBS III-TT) Vaccine to Prevent Vaginal Colonization With GBS III

BACKGROUND

Group B Streptococcus (GBS) frequently colonizes pregnant women and can cause sepsis and meningitis in young infants. If colonization was prevented through maternal immunization, a reduction in perinatal GBS disease might be possible. A GBS type III capsular polysaccharide (CPS)-tetanus toxoid conjugate (III-TT) vaccine was evaluated for safety and efficacy in preventing acquisition of GBS colonization.

METHODS

Healthy, nonpregnant women aged 18-40 years and screened to be GBS III vaginal and rectal culture negative were randomized to receive III-TT conjugate or tetanus diphtheria toxoid vaccine in a multicenter, observer-blinded trial. GBS vaginal and rectal cultures and blood were obtained bimonthly over 18 months. Serum concentrations of GBS III CPS-specific antibodies were determined using enzyme-linked immunosorbent assay.

RESULTS

Among 1525 women screened, 650 were eligible for the intent-to-treat analysis. For time to first acquisition of vaginal GBS III, vaccine efficacy was 36% (95% confidence interval [CI], 1%-58%; P = .044), and for first rectal acquisition efficacy was 43% (95% CI, 11% to 63%; P = .014). Two months post-immunization, geometric mean concentrations of serum GBS type III CPS-specific immunoglobulin G were 12.6 µg/mL (95% CI, 9.95 to 15.81) in GBS III-TT recipients, representing a 4-fold increase from baseline in 95% of women, which persisted. Both vaccines were well tolerated.

CONCLUSIONS

GBS CPS III-TT conjugate vaccine significantly delayed acquisition of vaginal and rectal GBS III colonization. In addition to its use for maternal immunization to passively protect infants with maternally derived antibodies, a multivalent vaccine might also serve to reduce fetal and neonatal exposure to GBS.

CLINICAL TRIALS REGISTRATION

NCT00128219.

Maternal Immunization

Vaccines administered to women during pregnancy can provide protection against serious infectious diseases for the mother, for the newborn, or both. Maternal immunization boosts the concentration of maternal antibodies that can be transferred across the placenta to directly protect infants too young to be immunized. In addition, indirect protection through prevention of maternal infection and through breast milk antibodies can be achieved through maternal immunization. In general, inactivated vaccines are considered safe for pregnant women and their fetuses, whereas live vaccines are avoided owing to the theoretical potential risk to the fetus. However, the risks and benefits of vaccination must be carefully weighed and whenever possible, protection to the mother and her infant should be prioritized. Influenza and tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccines are routinely recommended for all pregnant women in the United States. Seasonal inactivated influenza vaccine is recommended for all pregnant women in any trimester of pregnancy, mainly to protect the mother, but there is growing evidence that infants benefit from passive antibody protection against influenza complications. The Tdap vaccine is recommended during the third trimester of each pregnancy to provide optimal protection to infants who are at particularly high risk of pertussis complications and mortality in the first 3 months of life. The effects of maternal immunization on the prevention of maternal and infant disease have been demonstrated in observational and prospective studies of influenza and pertussis disease in the United States and worldwide. Maternal immunization has the potential to improve the health of mothers and young infants and therefore, other diseases of relevance during this period are now targets of active research and vaccine development, including group B streptococcus and respiratory syncytial virus. Similarly, several vaccines can be administered during pregnancy in special circumstances, when maternal health, travel, or other special situations arise. This article reviews the current recommendations for vaccination of women during pregnancy.

WHO consultation on group B Streptococcus vaccine development: Report from a meeting held on 27-28 April 2016

Globally, group B Streptococcus (GBS) remains a leading cause of sepsis and meningitis in infants in the first 90days of life. Intrapartum antibiotic prophylaxis (IAP) for women at increased risk of transmitting GBS to their newborns has been effective in reducing part, but not all, of the GBS disease burden in many high income countries (HICs). In low- and middle-income countries (LMICs), IAP use is low. Immunization of pregnant women with a GBS vaccine represents an alternative strategy to protecting newborns and young infants, through transplacental antibody transfer and potentially by reducing new vaginal colonization. This vaccination strategy was first suggested in the 1970s and several potential GBS vaccines have completed phase I/II clinical trials. During the 2015 WHO Product Development for Vaccines Advisory Committee meeting, GBS was identified as a high priority for the development of a vaccine for maternal immunization because of the major public health burden posed by GBS in LMICs, and the high technical feasibility for successful development. Following this meeting, the first WHO technical consultation on GBS vaccines was held on the 27th and 28th of April 2016, to consider development pathways for such vaccines, focused on their potential role in reducing newborn and young infant deaths and possibly stillbirths in LMICs. Discussion topics included: (1) pathophysiology of disease; (2) current gaps in the knowledge of global disease burden and serotype distribution; (3) vaccine candidates under development; (4) design considerations for phase III trials; and (5) pathways to licensure, policy recommendations and use. Efforts to address gaps identified in each of these areas are needed to establish the public health need for, the development and deployment of, efficacious GBS vaccines. In particular, more work is required to understand the global disease burden of GBS-associated stillbirths, and to develop quality-assured standardized antibody assays to identify correlates of protection.

Patient and provider perspectives on how trust influences maternal vaccine acceptance among pregnant women in Kenya

BACKGROUND

Pregnant women and newborns are at high risk for infectious diseases. Altered immunity status during pregnancy and challenges fully vaccinating newborns contribute to this medical reality. Maternal immunization is a strategy to protect pregnant women and their newborns. This study aimed to find out how patient-provider relationships affect maternal vaccine uptake, particularly in the context of a lower middle- income country where limited research in this area exists.

METHODS

We conducted semi-structured, in-depth narrative interviews of both providers and pregnant women from four sites in Kenya: Siaya, Nairobi, Mombasa, and Marsabit. Interviews were conducted in either English or one of the local regional languages.

RESULTS

We found that patient trust in health care providers (HCPs) is integral to vaccine acceptance among pregnant women in Kenya. The HCP-patient relationship is a fiduciary one, whereby the patients' trusts is primarily rooted in the provider's social position as a person who is highly educated in matters of health. Furthermore, patient health education and provider attitudes are crucial for reinstating and fostering that trust, especially in cases where trust was impeded by rumors, community myths and misperceptions, and religious and cultural factors.

CONCLUSION

Patient trust in providers is a strong facilitator contributing to vaccine acceptance among pregnant women in Kenya. To maintain and increase immunization trust, providers have a critical role in cultivating a positive environment that allows for favorable interactions and patient health education. This includes educating providers on maternal immunizations and enhancing knowledge of effective risk communication tactics in clinical encounters.

Novel Multiplex Immunoassays for Quantification of IgG against Group B Streptococcus Capsular Polysaccharides in Human Sera

Group B Streptococcus (GBS) infections constitute a major cause of invasive disease during the first three months of life and an unmet medical need that could be addressed by maternal vaccination. The GBS capsular polysaccharides (CPSs) have shown promise as vaccine targets in clinical studies. A highly specific serological assay to quantify maternal and neonatal anti-CPS antibody levels will be instrumental for GBS vaccine licensure. Here, we describe the development and comparison of two novel multiplex immunoassays (MIAs) based on the Luminex technology for the quantification of IgG antibodies recognizing the five most frequent GBS capsular variants (Ia, Ib, II, III, and V) out of the ten types identified. The first assay is based on the use of biotinylated CPSs coupled to streptavidin-derivatized magnetic microspheres (Biotin-CPS MIA), while the second is a sandwich assay with plain CPSs coupled to magnetic microspheres coated with polysaccharide-specific mouse monoclonal antibodies (Sandwich MIA). Both assays showed good specificity, linearity, and precision, although the Biotin-CPS MIA presented higher sensitivity and lower complexity than the Sandwich MIA. A panel of human sera representing a wide range of anti-CPS IgG concentrations was tested in parallel by the two assays, which resulted in comparable titers. Our data support the preservation of antigenic epitopes in the biotinylated polysaccharides and the suitability of the Biotin-CPS MIA for the precise determination of GBS anti-CPS IgG concentrations in human sera.IMPORTANCE Group B streptococcal infections can cause death in neonates up to 3 months of age. Intrapartum antibiotic prophylaxis in GBS-colonized mothers has limited early infections but has no impact after the first week of life. The development of a maternal vaccine to address this unmet medical need has been identified as a priority by the World Health Organization, and the GBS CPSs are considered the best antigen targets. However, to date there are no accepted standardized assays to measure immune responses to the investigational vaccines and for establishment of serocorrelates of protection. Here, we describe the performance of two microsphere-based pentaplex immunoassays for the determination of antibodies recognizing the five most frequent GBS serotypes. Our data confirm that an assay based on biotinylated polysaccharides coupled to streptavidin microspheres would be suitable for the intended purpose.

Maternal Immunization and Antenatal Care Situation Analysis (MIACSA) study protocol: a multiregional, cross-sectional analysis of maternal immunization delivery strategies to reduce maternal and neonatal morbidity and mortality

INTRODUCTION

Maternal immunization (MI) with tetanus toxoid containing vaccine, is a safe and cost-effective way of preventing neonatal tetanus. Given the prospect of introducing new maternal vaccines in the near future, it is essential to identify and understand current policies, practices and unmet needs for introducing and/or scaling up MI in low-income and middle-income countries (LMICs).

METHODS AND ANALYSIS

The Maternal Immunization and Antenatal Care Situation Analysis (MIACSA) is a mixed methods, cross-sectional study that will collect data in four phases: (1) a review of global databases for selected health indicators in 136 LMICs; (2) a structured online survey directed at Maternal, Newborn and Child Health and Expanded Programme on Immunization focal points in all 136 LMICs; (3) semistructured telephone interviews of 30 selected LMICs and (4) 10 week-long country visits, including key informant interviews, health facility visits and focus group discussions. The principal analyses will assess correlations between the various aspects of MI delivery strategies and proxy measures of health systems performance related to vaccine-preventable disease control. The primary outcome will be a typology of existing MI delivery models, and secondary outcomes will include country profiles of child and maternal health indicators, and a MI gaps and needs analysis.

ETHICS AND DISSEMINATION

The protocol was approved by the WHO Ethics Review Committee (ERC.0002908). The results will be made available in a project report and submitted for publication in peer-reviewed journals that will be shared broadly among global health decision-makers, researchers, product developers and country-level stakeholders.

Disease burden of neonatal invasive Group B Streptococcus infection in the Netherlands

BACKGROUND

Group B Streptococcus (GBS) is the leading cause of neonatal sepsis and meningitis worldwide. We aimed to estimate the current burden of neonatal invasive GBS disease in the Netherlands, as a first step in providing an evidence base for policy makers on the potential benefits of a future maternal GBS vaccine.

METHODS

Surveillance of neonatal invasive GBS occurs at the National Reference Laboratory for Bacterial Meningitis, where culture isolates from cerebrospinal fluid and blood are sent by diagnostic laboratories. From the number of cultures we estimated the incidence of neonatal (age 0-90 days) GBS meningitis and sepsis. We constructed a disease progression model informed by literature and expert consultation to estimate the disease burden of neonatal invasive GBS infection. As many neonates with a probable GBS sepsis are never confirmed by blood culture, we further estimated the disease burden of unconfirmed cases of probable GBS sepsis in sensitivity analyses.

RESULTS

An estimated 97 cases and 6.5 deaths occurred in the Netherlands in 2017 due to culture positive neonatal invasive GBS infection. This incidence comprised 15 cases of meningitis and 42 cases of sepsis per 100.000 births, with an estimated mortality of 3.8 per 100.000 live births. A disease burden of 780 disability-adjusted life years (DALY) (95% CI 650-910) or 460 DALY per 100.000 live births was attributed to neonatal invasive GBS infection. In the sensitivity analysis including probable neonatal GBS sepsis the disease burden increased to 71 cases and 550 DALY (95% CI 460-650) per 100.000 live births.

CONCLUSION

In conclusion, neonatal invasive GBS infection currently causes a substantial disease burden in the Netherlands. However, important evidence gaps are yet to be filled. Furthermore, cases of GBS sepsis lacking a positive blood culture may contribute considerably to this burden potentially preventable by a future GBS vaccine.

Surface Structures of Group B Streptococcus Important in Human Immunity

The surface of the Gram-positive opportunistic pathogen Streptococcus agalactiae, or group B Streptococcus (GBS), harbors several carbohydrate and protein antigens with the potential to be effective vaccines. Capsular polysaccharides of all clinically-relevant GBS serotypes coupled to immunogenic proteins of both GBS and non-GBS origin have undergone extensive testing in animals that led to advanced clinical trials in healthy adult women. In addition, GBS proteins either alone or in combination have been tested in animals; a fusion protein construct has recently advanced to human clinical studies. Given our current understanding of the antigenicity and immunogenicity of the wide array of GBS surface antigens, formulations now exist for the generation of viable vaccines against diseases caused by GBS.

Epidemiology of Invasive Early-Onset and Late-Onset Group B Streptococcal Disease in the United States, 2006 to 2015: Multistate Laboratory and Population-Based Surveillance

IMPORTANCE

Invasive disease owing to group B Streptococcus (GBS) remains an important cause of illness and death among infants younger than 90 days in the United States, despite declines in early-onset disease (EOD; with onset at 0-6 days of life) that are attributed to intrapartum antibiotic prophylaxis (IAP). Maternal vaccines to prevent infant GBS disease are currently under development.

OBJECTIVE

To describe incidence rates, case characteristics, antimicrobial resistance, and serotype distribution of EOD and late-onset disease (LOD; with onset at 7-89 days of life) in the United States from 2006 to 2015 to inform IAP guidelines and vaccine development.

DESIGN, SETTING, AND PARTICIPANTS

This study used active population-based and laboratory-based surveillance for invasive GBS disease conducted through Active Bacterial Core surveillance in selected counties of 10 states across the United States. Residents of Active Bacterial Core surveillance areas who were younger than 90 days and had invasive GBS disease in 2006 to 2015 were included. Data were analyzed from December 2017 to April 2018.

EXPOSURES

Group B Streptococcus isolated from a normally sterile site.

MAIN OUTCOMES AND MEASURES

Early-onset disease and LOD incidence rates and associated GBS serotypes and antimicrobial resistance.

RESULTS

The Active Bacterial Core surveillance program identified 1277 cases of EOD and 1387 cases of LOD. From 2006 to 2015, EOD incidence declined significantly from 0.37 to 0.23 per 1000 live births (P < .001), and LOD rates remained stable (mean, 0.31 per 1000 live births). Among the mothers of 1277 infants with EOD, 617 (48.3%) had no indications for IAP and did not receive it, and 278 (21.8%) failed to receive IAP despite having indications. Serotype data were available for 1743 of 1897 patients (91.3%) from 7 sites that collect GBS isolates. Among patients with EOD, serotypes Ia (242 [27.3%]) and III (242 [27.3%]) were most common. Among patients with LOD, serotype III was most common (481 [56.2%]), and this increased from 2006 to 2015 from 0.12 to 0.20 cases per 1000 live births (P < .001). Serotype IV caused 53 cases (6.2%) of EOD and LOD combined. The 6 most common serotypes (Ia, Ib, II, III, IV, and V) caused 881 EOD cases (99.3%) and 853 LOD cases (99.7%). No β-lactam resistance was identified; 359 isolates (20.8%) tested showed constitutive clindamycin resistance. In 2015, an estimated 840 EOD cases and 1265 LOD cases occurred nationally.

CONCLUSIONS AND RELEVANCE

The rates of LOD among US infants are now higher than EOD rates. Combined with addressing IAP implementation gaps, an effective vaccine covering the most common serotypes might further reduce EOD rates and help prevent LOD, for which there is no current public health intervention.

Conformation and Cross-Protection in Group B Streptococcus Serotype III and Streptococcus pneumoniae Serotype 14: A Molecular Modeling Study

Although the branched capsular polysaccharides of Streptococcus agalactiae serotype III (GBSIII PS) and Streptococcus pneumoniae serotype 14 (Pn14 PS) differ only in the addition of a terminal sialic acid on the GBSIII PS side chains, these very similar polysaccharides are immunogenically distinct. Our simulations of GBSIII PS, Pn14 PS and the unbranched backbone polysaccharide provide a conformational rationale for the different antigenic epitopes identified for these PS. We find that side chains stabilize the proximal βdGlc(1→6)βdGlcNAc backbone linkage, restricting rotation and creating a well-defined conformational epitope at the branch point. This agrees with the glycotope structure recognized by an anti-GBSIII PS functional monoclonal antibody. We find the same dominant solution conformation for GBSIII and Pn14 PS: aside from the branch point, the backbone is very flexible with a “zig-zag” conformational habit, rather than the helix previously proposed for GBSIII PS. This suggests a common strategy for bacterial evasion of the host immune system: a flexible backbone that is less perceptible to the immune system, combined with conformationally-defined branch points presenting human-mimic epitopes. This work demonstrates how small structural features such as side chains can alter the conformation of a polysaccharide by restricting rotation around backbone linkages.

Group B Streptococcus (GBS) Colonization and Disease among Pregnant Women: A Historical Cohort Study

Background

Maternal GBS colonization is associated with early-onset neonatal sepsis and extensive efforts are directed to preventing this complication. Less is known about maternal risks of GBS colonization. We seek to provide a modern estimate of the incidence and impact of maternal GBS colonization and invasive GBS disease.

Methods

A single center historical cohort study of all births between 2003 and 2015 was performed. Data was collected via electronic health record abstraction using an institutional specific tool. Descriptive statistics were performed regarding GBS status. Inferential statistics were performed comparing risk of adverse pregnancy outcomes in cohorts with and without GBS colonization as well as cohorts with GBS colonization and invasive GBS disease.

Results

A total of 60,029 deliveries were included for analysis. Overall, 21.6% of the population was GBS colonized and 0.1% had invasive GBS disease. GBS colonization was associated with younger maternal age, Black race, non-Hispanic ethnicity, chronic hypertension, preexisting diabetes, and tobacco use (p<0.01). In the adjusted analyses, there was an increased risk of gestational diabetes (aRR 1.21, 95% CI 1.11-1.32) in colonized pregnancies and a decreased incidence of short cervix (aRR 0.64, 95% CI 0.52-0.79), chorioamnionitis (aRR 0.76, 95% CI 0.66-0.87), wound infection (aRR 0.75, 95% CI 0.64-0.88), and operative delivery (aRR 0.85, 95% CI 0.83-0.88).

Conclusions

This modern-day large cohort of all births over a 12-year period demonstrates a GBS colonization rate of 21.6%. This data reflects a need to assess maternal and perinatal outcomes in addition to neonatal GBS sepsis rates to inform decisions regarding the utility of maternal vaccination.

Serocorrelates of protection against infant group B streptococcus disease

Group B streptococcus (GBS) is a leading cause of young infant mortality and morbidity globally, with vaccines being developed for over four decades but none licensed to date. A serocorrelate of protection against invasive disease in young infants is being considered to facilitate vaccine early licensure, followed by demonstration of efficacy assessed postlicensure. In this Review, we synthesise the available scientific evidence to define an immune correlate associated with GBS disease risk reduction on the basis of studies of natural infection. We summarise studies that have investigated GBS serum anticapsular or anti-protein antibodies, and studies measuring the association between antibody function and disease risk reduction. We highlight how knowledge on the development of correlates of protection from existing vaccines could be harnessed to facilitate GBS vaccine development. These lessons include aggregation of serocorrelates of protection for individual serotypes, understanding the relationship between immunity derived from natural exposure of adults and vaccine-induced immunity, or using extrapolation of protection from in-vitro immunoassay results. We also highlight key considerations for the assessment of the role of antibodies to derive a serocorrelate of risk reduction in future seroepidemiological studies of GBS disease.

Maternal immunisation to improve the health of HIV-exposed infants

HIV-exposed but uninfected (HEU) infants are at an increased risk of many infectious diseases that can contribute to the high mortality seen among HEU children. Maternal immunisation could be a promising strategy to reduce infections in HEU infants. However, very little research has explored the effect of HIV on the immunogenicity and effectiveness of vaccines given during pregnancy. We review the available evidence on maternal immunisation among women living with HIV (WLWH) for all vaccines recommended, considered, or being investigated for routine or risk-based use during pregnancy. Of the 11 vaccines included, only three have been investigated in WLWH. Available evidence suggests that maternal HIV infection limits the immunogenicity of several vaccines, leaving HEU infants more susceptible to infection during their first few months of life. Whether maternal immunisation reduces the infectious morbidity and mortality associated with infectious diseases in HEU children remains unknown. We conclude the Review by identifying future research priorities.

Clinical Characteristics and Risk Factors for Poor Outcome in Infants Less Than 90 Days of Age With Bacterial Meningitis in the United Kingdom and Ireland

BACKGROUND

To describe the clinical characteristics and risk factors associated with poor outcome in infants <90 days of age with bacterial meningitis.

METHODS

Prospective, enhanced, national population-based active surveillance for infants <90 days of age with bacterial meningitis in the United Kingdom and Ireland between July 2010 and July 2011. Infants were identified through the British Paediatric Surveillance Unit, laboratory surveillance and meningitis charities.

RESULTS

Clinical details was available for 263 of 298 (88%) infants where a bacterium was identified, 184 (70%) were born at term. Fever was reported in 143 (54%), seizures in 73 (28%), bulging fontanelle in 58 (22%), coma in 15 (6%) and neck stiffness in 7 (3%). Twenty-three (9%) died and 56/240 (23%) of the survivors had serious central nervous system complications at discharge. Temperature instability [odds ratio (OR), 2.99; 95% confidence interval (CI): 1.21-7.41], seizures (OR, 7.06; 95% CI: 2.80-17.81), cerebrospinal fluid protein greater than the median concentration (2275 mg/dL; OR, 2.62; 95% CI: 1.13-6.10) and pneumococcal meningitis (OR, 4.83; 95% CI: 1.33-17.58) were independently associated with serious central nervous system complications while prematurity (OR, 5.84; 95% CI: 2.02-16.85), low birthweight (OR, 8.48; 95% CI: 2.60-27.69), coma at presentation (OR, 31.85; 95% CI: 8.46-119.81) and pneumococcal meningitis (OR, 4.62; 95% CI: 1.19-17.91) were independently associated with death.

CONCLUSIONS

The classic features of meningitis were uncommon. The presentation in young infants is often nonspecific, and only half of cases presented with fever. A number of clinical and laboratory factors were associated with poor outcomes; further research is required to determine how knowledge of these risk factors might improve clinical management and outcomes.

Systematic review of the clinical development of group B streptococcus serotype-specific capsular polysaccharide-based vaccines

INTRODUCTION

Vaccination against group B Streptococcus (GBS) during pregnancy could provide protection against disease in the mother, fetus, and newborn. Immunity through transplacental acquired antibodies in the newborns could persist through early infancy, reducing the risk of early-onset (<7 days age) and late-onset (7-89 days age) disease. We conducted a systematic review of clinical trials on GBS capsular polysaccharide (CPS) vaccine to assess its safety and immunogenicity in pregnant and nonpregnant adults.

AREAS COVERED

We searched literature databases PubMed (Medline), Scopus, and the Cochrane library and identified 25 unique records on GBS CPS vaccines with or without conjugant protein.

EXPERT COMMENTARY

GBS vaccines were well tolerated, with mild local reactogenicity being the main solicited adverse event and no difference in reporting of other serious adverse events compared to placebo recipients. CPS vaccines conjugated to immunogenic proteins induced ≥fourfold increase of serotype-specific antibodies with high longevity (1-2 years); and capable of promoting homotypic GBS opsonophagocytic killing. Feto-maternal transplacental antibody ratio of serotype-specific IgG ranged between 0.49 and 0.81. The clinical relevance of these immunogenicity studies, however, need to be weighed against a correlate of protection against invasive GBS disease in infants, which is yet to be established using a universally accepted standardized assay.

Antibody Kinetics and Response to Routine Vaccinations in Infants Born to Women Who Received an Investigational Trivalent Group B Streptococcus Polysaccharide CRM197-Conjugate Vaccine During Pregnancy

Background

Maternal vaccination against group B Streptococcus (GBS) might provide protection against invasive GBS disease in infants. We investigated the kinetics of transplacentally transferred GBS serotype-specific capsular antibodies in the infants and their immune response to diphtheria toxoid and pneumococcal vaccination.

Methods

This phase 1b/2, observer-blind, single-center study (NCT01193920) enrolled infants born to women previously randomized (1:1:1:1) to receive either GBS vaccine at dosages of 0.5, 2.5, or 5.0 μg of each of 3 CRM₁₉₇-glycoconjugates (serotypes Ia, Ib, and III), or placebo. Infants received routine immunization: combination diphtheria vaccine (diphtheria-tetanus-acellular pertussis–inactivated poliovirus/Haemophilus influenzae type b vaccine; age 6/10/ 14 weeks) and 13-valent pneumococcal CRM₁₉₇-conjugate vaccine (PCV13; age 6/14 weeks and 9 months). Antibody levels were assessed at birth, day (D) 43, and D91 for GBS serotypes; 1 month postdose 3 (D127) for diphtheria; and 1 month postprimary (D127) and postbooster (D301) doses for pneumococcal serotypes.

Results

Of 317 infants enrolled, 295 completed the study. In infants of GBS vaccine recipients, GBS serotype-specific antibody geometric mean concentrations were significantly higher than in the placebo group at all timepoints and predictably decreased to 41%–61% and 26%–76% of birth levels by D43 and D91, respectively. Across all groups, ≥95% of infants were seroprotected against diphtheria at D127 and ≥91% of infants had seroprotective antibody levels against each PCV13 pneumococcal serotype at D301.

Conclusions

Maternal vaccination with an investigational CRM₁₉₇-glycoconjugate GBS vaccine elicited higher GBS serotype-specific antibody levels in infants until 90 days of age, compared with a placebo group, and did not affect infant immune responses to diphtheria toxoid and pneumococcal vaccination.

Clinical Trials Registration

NCT01193920.

Maternal immunization

Pregnant women, neonates, and infants are at higher risk for severe infections due to vaccine-preventable diseases. Very young infants rarely respond well to vaccination due to poor immunogenicity and interference from maternal antibody. Maternal immunization protects the mother and fetus from disease and protects the infant through transplacental antibody transfer through the first 6 months of life. Currently, immunizations routinely recommended during pregnancy include inactivated influenza, tetanus toxoid, and acellular pertussis vaccines. Promising maternal vaccine candidates in development include a group B streptococcus vaccine and a respiratory syncytial virus vaccine. Birth Defects Research 109:379-386, 2017. © 2017 Wiley Periodicals, Inc.

Group B Streptococcal Colonization, Molecular Characteristics, and Epidemiology

Streptococcus agalactiae or group B streptococcus (GBS) is a leading cause of serious neonatal infections. GBS is an opportunistic commensal constituting a part of the intestinal and vaginal physiologic flora and maternal colonization is the principal route of GBS transmission. GBS is a pathobiont that converts from the asymptomatic mucosal carriage state to a major bacterial pathogen causing severe invasive infections. At present, as many as 10 serotypes (Ia, Ib, and II–IX) are recognized. The aim of the current review is to shed new light on the latest epidemiological data and clonal distribution of GBS in addition to discussing the most important colonization determinants at a molecular level. The distribution and predominance of certain serotypes is susceptible to variations and can change over time. With the availability of multilocus sequence typing scheme (MLST) data, it became clear that GBS strains of certain clonal complexes possess a higher potential to cause invasive disease, while other harbor mainly colonizing strains. Colonization and persistence in different host niches is dependent on the adherence capacity of GBS to host cells and tissues. Bacterial biofilms represent well-known virulence factors with a vital role in persistence and chronic infections. In addition, GBS colonization, persistence, translocation, and invasion of host barriers are largely dependent on their adherence abilities to host cells and extracellular matrix proteins (ECM). Major adhesins mediating GBS interaction with host cells include the fibrinogen-binding proteins (Fbs), the laminin-binding protein (Lmb), the group B streptococcal C5a peptidase (ScpB), the streptococcal fibronectin binding protein A (SfbA), the GBS immunogenic bacterial adhesin (BibA), and the hypervirulent adhesin (HvgA). These adhesins facilitate persistent and intimate contacts between the bacterial cell and the host, while global virulence regulators play a major role in the transition to invasive infections. This review combines for first time epidemiological data with data on adherence and colonization for GBS. Investigating the epidemiology along with understanding the determinants of mucosal colonization and the development of invasive disease at a molecular level is therefore important for the development of strategies to prevent invasive GBS disease worldwide.

Invasive bacterial disease trends and characterization of group B streptococcal isolates among young infants in southern Mozambique, 2001-2015

Background

Maternal group B streptococcal (GBS) vaccines under development hold promise to prevent GBS disease in young infants. Sub-Saharan Africa has the highest estimated disease burden, although data on incidence and circulating strains are limited. We described invasive bacterial disease (IBD) trends among infants <90 days in rural Mozambique during 2001–2015, with a focus on GBS epidemiology and strain characteristics.

Methods

Community-level birth and mortality data were obtained from Manhiça’s demographic surveillance system. IBD cases were captured through ongoing surveillance at Manhiça district hospital. Stored GBS isolates from cases underwent serotyping by multiplex PCR, antimicrobial susceptibility testing, and whole genome sequencing.

Results

There were 437 IBD cases, including 57 GBS cases. Significant declines in overall IBD, neonatal mortality, and stillbirth rates were observed (P<0.0001), but not for GBS (P = 0.17). In 2015, GBS was the leading cause of young infant IBD (2.7 per 1,000 live births). Among 35 GBS isolates available for testing, 31 (88.6%) were highly related serotype III isolates within multilocus sequence types (STs) 17 (68.6%) or 109 (20.0%). All seven ST109 isolates (21.9%) had elevated minimum inhibitory concentration (MIC) to penicillin (≥0.12 μg/mL) associated with penicillin-binding protein (PBP) 2x substitution G398A. Epidemiologic and molecular data suggest this is a well-established clone.

Conclusion

A notable young infant GBS disease burden persisted despite improvements in overall maternal and neonatal health. We report an established strain with pbp2x point mutation, a first-step mutation associated with reduced penicillin susceptibility within a well-known virulent lineage in rural Mozambique. Our findings further underscores the need for non-antibiotic GBS prevention strategies.

Factors influencing access of pregnant women and their infants to their local healthcare system: a prospective, multi-centre, observational study

Background

The successful implementation of maternal vaccination relies on results of clinical trials, considering the prenatal and postnatal attendance at selected healthcare institutions. This study evaluated factors influencing maternal/infant access to healthcare facilities to identify potential barriers to participation in future clinical trials on maternal vaccination.

Methods

In this prospective, multi-centre, observational study, pregnant women (N = 3243) were enrolled at ten sites across Panama, the Dominican Republic, South Africa, and Mozambique between 2012 and 2014. They completed questionnaires at enrolment, delivery, and infant follow-up (90 days post-partum) visits, including questions on transportation, phone accessibility, alternative childcare, gestational age at enrolment, delivery location, and health status of their infant. Logistic regression was used to identify factors significantly associated with return to study site for delivery or infant follow-up visits.

Results

Among 3229 enrolled women with delivery information, 63.6% (range across sites: 25.3–91.5%) returned to study site for delivery. Older women and those at later gestational age at enrolment were more likely to deliver at the study site. While heterogeneities were observed at site level, shorter travel time at delivery and increased transportation costs at enrolment were associated with increased likelihood of women returning to study site for delivery. Among 3145 women with live-born infants, 3077 (95.3%) provided 90-day follow-up information; of these, 68.9% (range across sites: 25.6–98.9%) returned to study site for follow-up visits. Women with other children and with lower transportation costs at delivery were more likely to return to study site for follow-up visits. Among 666 infants reported sick, 94.3% were taken to a healthcare facility, with only 41.9% (range across sites: 4.9–77.3%) to the study site.

Conclusion

Although high retention was observed from enrolment through 90 days after delivery, post-partum surveillance should be broadened beyond the study sites and additional follow-up visits should be planned within the neonatal period. The factors influencing maternal/infant access to healthcare facilities and the issues identified in this study should be taken into consideration in planning future clinical studies on maternal immunisation in low- and middle-income countries.

Trial registration

The study was registered at ClinicalTrial.gov (NCT01734434) on November 22, 2012.

Electronic supplementary material

The online version of this article (10.1186/s12884-017-1655-3) contains supplementary material, which is available to authorized users.