Effect of a 2+1 schedule of ten-valent versus 13-valent pneumococcal conjugate vaccine on pneumococcal carriage: Results from a randomised controlled trial in Vietnam

Streptococcus pneumoniae serotype 33G: genetic, serological, and structural analysis of a new capsule type

IMPORTANCE

Streptococcus pneumoniae (the pneumococcus) is a bacterial pathogen with the greatest burden of disease in Asia and Africa. The pneumococcal capsular polysaccharide has biological relevance as a major virulence factor as well as public health importance as it is the target for currently licensed vaccines. These vaccines have limited valency, covering up to 23 of the >100 known capsular types (serotypes) with higher valency vaccines in development. Here, we have characterized a new pneumococcal serotype, which we have named 33G. We detected serotype 33G in nasopharyngeal swabs (n = 20) from children and adults hospitalized with pneumonia, as well as healthy children in Mongolia. We show that the genetic, serological, and biochemical properties of 33G differ from existing serotypes, satisfying the criteria to be designated as a new serotype. Future studies should focus on the geographical distribution of 33G and any changes in prevalence following vaccine introduction.

Emerging vaccine strategies against the incessant pneumococcal disease

The incidence of invasive pneumococcal disease (IPD) caused by infection with the pathogen Streptococcus pneumoniae (Spn) has been on a downward trend for decades due to worldwide vaccination programs. Despite the clinical successes observed, the Center for Disease Control (CDC) reports that the continued global burden of S. pneumoniae will be in the millions each year, with a case-fatality rate hovering around 5%. Thus, it is a top priority to continue developing new Spn vaccination strategies to harness immunological insight and increase the magnitude of protection provided. As emphasized by the World Health Organization (WHO), it is also crucial to broaden the implementation of vaccines that are already obtainable in the clinical setting. This review focuses on the immune mechanisms triggered by existing pneumococcal vaccines and provides an overview of the current and upcoming clinical strategies being employed. We highlight the associated challenges of serotype selectivity and using pneumococcal-derived proteins as alternative vaccine antigens.

Efficacy against pneumococcal carriage and the immunogenicity of reduced-dose (0 + 1 and 1 + 1) PCV10 and PCV13 schedules in Ho Chi Minh City, Viet Nam: a parallel, single-blind, randomised controlled trial

BACKGROUND

Interest in reduced-dose pneumococcal conjugate vaccine (PCV) schedules is growing, but data on their ability to provide direct and indirect protection are scarce. We evaluated 1 + 1 (at 2 months and 12 months) and 0 + 1 (at 12 months) schedules of PCV10 or PCV13 in a predominately unvaccinated population.

METHODS

In this parallel, single-blind, randomised controlled trial, healthy infants aged 2 months were recruited from birth records in three districts in Ho Chi Minh City, Vietnam, and assigned (4:4:4:4:9) to one of five groups: PCV10 at 12 months of age (0 + 1 PCV10), PCV13 at 12 months of age (0 + 1 PCV13), PCV10 at 2 months and 12 months of age (1 + 1 PCV10), PCV13 at 2 months and 12 months of age (1 + 1 PCV13), and unvaccinated control. Outcome assessors were masked to group allocation, and the infants' caregivers and those administering vaccines were not. Nasopharyngeal swabs collected at 6 months, 12 months, 18 months, and 24 months were analysed for pneumococcal carriage. Blood samples collected from a subset of participants (200 per group) at various timepoints were analysed by ELISA and opsonophagocytic assay. The primary outcome was the efficacy of each schedule against vaccine-type carriage at 24 months, analysed by intention to treat for all those with a nasopharyngeal swab available. This trial is registered at ClinicalTrials.gov, NCT03098628.

FINDINGS

2501 infants were enrolled between March 8, 2017, and July 24, 2018 and randomly assigned to study groups (400 to 0 + 1 PCV10, 400 to 0 + 1 PCV13, 402 to 1 + 1 PCV10, 401 to 1 + 1 PCV13, and 898 to control). Analysis of the primary endpoint included 341 participants for 0 + 1 PCV10, 356 0 + 1 PCV13, 358 1 + 1 PCV10, 350 1 + 1 PCV13, and 758 control. At 24 months, a 1 + 1 PCV10 schedule reduced PCV10-type carriage by 58% (95% CI 25 to 77), a 1 + 1 PCV13 schedule reduced PCV13-type carriage by 65% (42 to 79), a 0 + 1 PCV10 schedule reduced PCV10-type carriage by 53% (17 to 73), and a 0 + 1 PCV13 schedule non-significantly reduced PCV13-type carriage by 25% (-7 to 48) compared with the unvaccinated control group. Reactogenicity and serious adverse events were similar across groups.

INTERPRETATION

A 1 + 1 PCV schedule greatly reduces vaccine-type carriage and is likely to generate substantial herd protection and provide some degree of individual protection during the first year of life. Such a schedule is suitable for mature PCV programmes or for introduction in conjunction with a comprehensive catch-up campaign, and potentially could be most effective given as a mixed regimen (PCV10 then PCV13). A 0 + 1 PCV schedule has some effect on carriage along with a reasonable immune response and could be considered for use in humanitarian crises or remote settings.

FUNDING

Bill & Melinda Gates Foundation.

TRANSLATION

For the Vietnamese translation of the abstract see Supplementary Materials section.

Molecular Epidemiology of Streptococcus pneumoniae Detected in Hospitalized Pediatric Acute Respiratory Infection Cases in Central Vietnam

Streptococcus pneumoniae is the major bacterial pathogen causing high pneumonia morbidity and mortality in children <5 years of age. This study aimed to determine the molecular epidemiology of S. pneumoniae detected among hospitalized pediatric ARI cases at Khanh Hoa General Hospital, Nha Trang, Vietnam, from October 2015 to September 2016 (pre-PCV). We performed semi-quantitative culture to isolate S. pneumoniae. Serotyping, antimicrobial susceptibility testing, resistance gene detection and multi-locus sequence typing were also performed. During the study period, 1300 cases were enrolled and 413 (31.8%) S. pneumoniae were isolated. School attendance, age <3 years old and prior antibiotic use before admission were positively associated with S. pneumoniae isolation. Major serotypes were 6A/B (35.9%), 19F (23.7%) and 23F (12.7%), which accounted for 80.3% of vaccine-type pneumococci. High resistance to Clarithromycin, Erythromycin and Clindamycin (86.7%, 85%, 78.2%) and the mutant drug-resistant genes pbp1A (98.1%), pbp2b (98.8%), pbp2x (99.6%) ermB (96.6%) and mefA (30.3%) were detected. MLST data showed high genetic diversity among the isolates with dominant ST 320 (21.2%) and ST 13223 (19.3%), which were mainly found in Vietnam. Non-typeables accounted for most of the new STs found in the study. Vaccine-type pneumococcus and macrolide resistance were commonly detected among hospitalized pediatric ARI cases.

Immunogenicity and seroefficacy of 10-valent and 13-valent pneumococcal conjugate vaccines: a systematic review and network meta-analysis of individual participant data

Background

Vaccination of infants with pneumococcal conjugate vaccines (PCV) is recommended by the World Health Organization. Evidence is mixed regarding the differences in immunogenicity and efficacy of the different pneumococcal vaccines.

Methods

In this systematic-review and network meta-analysis, we searched the Cochrane Library, Embase, Global Health, Medline, clinicaltrials.gov and trialsearch.who.int up to February 17, 2023 with no language restrictions. Studies were eligible if they presented data comparing the immunogenicity of either PCV7, PCV10 or PCV13 in head-to-head randomised trials of young children under 2 years of age, and provided immunogenicity data for at least one time point after the primary vaccination series or the booster dose. Publication bias was assessed via Cochrane's Risk Of Bias due to Missing Evidence tool and comparison-adjusted funnel plots with Egger's test. Individual participant level data were requested from publication authors and/or relevant vaccine manufacturers. Outcomes included the geometric mean ratio (GMR) of serotype-specific IgG and the relative risk (RR) of seroinfection. Seroinfection was defined for each individual as a rise in antibody between the post-primary vaccination series time point and the booster dose, evidence of presumed subclinical infection. Seroefficacy was defined as the RR of seroinfection. We also estimated the relationship between the GMR of IgG one month after priming and the RR of seroinfection by the time of the booster dose. The protocol is registered with PROSPERO, ID CRD42019124580.

Findings

47 studies were eligible from 38 countries across six continents. 28 and 12 studies with data available were included in immunogenicity and seroefficacy analyses, respectively. GMRs comparing PCV13 vs PCV10 favoured PCV13 for serotypes 4, 9V, and 23F at 1 month after primary vaccination series, with 1.14- to 1.54- fold significantly higher IgG responses with PCV13. Risk of seroinfection prior to the time of booster dose was lower for PCV13 for serotype 4, 6B, 9V, 18C and 23F than for PCV10. Significant heterogeneity and inconsistency were present for most serotypes and for both outcomes. Two-fold higher antibody after primary vaccination was associated with a 54% decrease in risk of seroinfection (RR 0.46, 95% CI 0.23-0.96).

Interpretation

Serotype-specific differences were found in immunogenicity and seroefficacy between PCV13 and PCV10. Higher antibody response after vaccination was associated with a lower risk of subsequent infection. These findings could be used to compare PCVs and optimise vaccination strategies.

Funding

The NIHR Health Technology Assessment Programme.

A systematic review of pneumococcal conjugate vaccine impact on pneumococcal nasopharyngeal colonisation density in children under 5 years of age

BACKGROUND

High pneumococcal carriage density has been associated with severe pneumonia in some settings. The impact of pneumococcal conjugate vaccines (PCVs) on pneumococcal carriage density has been variable. The aim of this systematic literature review is to describe the effect of PCV7, PCV10 and PCV13 on pneumococcal colonisation density in children under five years old.

METHODS

We included peer reviewed English literature published between 2000 and 2021 to identify relevant articles using Embase, Medline and PubMed. Original research articles of any study design in countries where PCV has been introduced/studied were included. Quality (risk) assessment was performed using tools developed by the National Heart Brain and Lung Institute for inclusion in this review. We used a narrative synthesis to present results.

RESULTS

Ten studies were included from 1941 articles reviewed. There were two randomised controlled trials, two cluster randomised trials, one case control study, one retrospective cohort study and four cross sectional studies. Three studies used semiquantitative culture methods to determine density while the remaining studies used quantitative molecular techniques. Three studies reported an increase in density and three studies found a decrease in density among vaccinated compared with unvaccinated children. Four studies found no effect. There was considerable heterogeneity in the study populations, study design and laboratory methods.

CONCLUSION

There was no consensus regarding the impact of PCV on pneumococcal nasopharyngeal density. We recommend the use of standardised methods to evaluate PCV impact on density.

Estimating the economic burden of respiratory syncytial virus infections in infants in Vietnam: a cohort study

BACKGROUND

Little information is available on the costs of respiratory syncytial virus (RSV) in Vietnam or other low- and middle-income countries. Our study estimated the costs of LRTIs associated with RSV infection among children in southern Vietnam.

METHODS

We conducted a prospective cohort study evaluating household and societal costs associated with LRTIs stratified by RSV status and severity among children under 2 years old who sought care at a major pediatric referral hospital in southern Vietnam. Enrollment periods were September 2019-December 2019, October 2020-June 2021 and October 2021-December 2021. RSV status was confirmed by a validated RT-PCR assay. RSV rapid detection antigen (RDA) test performance was also evaluated. Data on resource utilization, direct medical and non-medical costs, and indirect costs were collected from billing records and supplemented by patient-level questionnaires. All costs are reported in 2022 US dollars.

RESULTS

536 children were enrolled in the study, with a median age of 7 months (interquartile range [IQR] 3-12). This included 210 (39.2%) children from the outpatient department, 318 children (59.3%) from the inpatient respiratory department (RD), and 8 children (1.5%) from the intensive care unit (ICU). Nearly 20% (105/536) were RSV positive: 3.9 percent (21/536) from the outpatient department, 15.7% (84/536) from the RD, and none from the ICU. The median total cost associated with LRTI per patient was US$52 (IQR 32-86) for outpatients and US$184 (IQR 109-287) for RD inpatients. For RSV-associated LRTIs, the median total cost per infection episode per patient was US$52 (IQR 32-85) for outpatients and US$165 (IQR 95-249) for RD inpatients. Total out-of-pocket costs of one non-ICU admission of RSV-associated LRTI ranged from 32%-70% of the monthly minimum wage per person (US$160) in Ho Chi Minh City. The sensitivity and the specificity of RSV RDA test were 88.2% (95% CI 63.6-98.5%) and 100% (95% CI 93.3-100%), respectively.

CONCLUSION

These are the first data reporting the substantial economic burden of RSV-associated illness in young children in Vietnam. This study informs policymakers in planning health care resources and highlights the urgency of RSV disease prevention.

Effect of different schedules of ten-valent pneumococcal conjugate vaccine on pneumococcal carriage in Vietnamese infants: results from a randomised controlled trial

Background

WHO recommends a three-dose infant pneumococcal conjugate vaccine (PCV) schedule administered as a two-dose primary series with booster (2 + 1) or a three-dose primary series (3 + 0). Data on carriage impacts of these and further reduced PCV schedules are needed to inform PCV strategies. Here we evaluate the efficacy against carriage of four different PCV10 schedules.

Methods

Participants within an open-label, randomised controlled trial in Ho Chi Minh City, Vietnam, were allocated to receive PCV10 in a 3 + 1 (2,3,4,9 months, n = 152), 3 + 0 (2,3,4 months, n = 149), 2 + 1 (2,4,9.5 months, n = 250) or novel two-dose (2,6 months, n = 202) schedule, or no infant doses of PCV (two control groups, n = 197 and n = 199). Nasopharyngeal swabs collected between 2 and 24 months were analysed (blinded) for pneumococcal carriage and serotypes. Trial registration: ClinicalTrials.gov NCT01953510.

Findings

Pneumococcal carriage prevalence was low (10.6-14.1% for vaccine-type (VT) at 12-24 months in unvaccinated controls). All four PCV10 schedules reduced VT carriage compared with controls (the 2 + 1 schedule at 12, 18, and 24 months; the 3 + 1 and two-dose schedules at 18 months; and the 3 + 0 schedule at 24 months), with maximum reductions of 40.1%-64.5%. There were no differences in VT carriage prevalence at 6 or 9 months comparing three-dose and two-dose primary series, and no differences at 12, 18, or 24 months when comparing schedules with and without a booster dose.

Interpretation

In Vietnamese children with a relatively low pneumococcal carriage prevalence, 3 + 1, 2 + 1, 3 + 0 and two-dose PCV10 schedules were effective in reducing VT carriage. There were no discernible differences in the effect on carriage of the WHO-recommended 2 + 1 and 3 + 0 schedules during the first two years of life. Together with the previously reported immunogenicity data, this trial suggests that a range of PCV schedules are likely to generate significant direct and indirect protection.

Funding

NHMRC, BMGF.

Simplified 0+1 and 1+1 pneumococcal vaccine schedules in Ho Chi Minh City, Vietnam: protocol for a randomised controlled trial

INTRODUCTION

Reduced-dose schedules offer a more efficient and affordable way to use pneumococcal conjugate vaccines (PCVs). Such schedules rely primarily on the maintenance of herd protection. The Vietnam Pneumococcal Trial II (VPT-II) will evaluate reduced-dose schedules of PCV10 and PCV13 utilising an unvaccinated control group. Schedules will be compared in relation to their effect on nasopharyngeal carriage and immunogenicity.

METHODS AND ANALYSIS

VPT-II is a single-blind open-label randomised controlled trial of 2500 infants in three districts of Ho Chi Minh City, Vietnam. Eligible infants have no clinically significant maternal or perinatal history and are born at or after 36 weeks' gestation. Participants are recruited at 2 months of age and randomly assigned (4:4:4:4:9) using block randomisation, stratified by district, to one of five groups: four intervention groups that receive PCV10 in a 0+1 (at 12 months) or 1+1 (at 2 and 12 months) schedule or PCV13 in the same 0+1 or 1+1 schedule; and a control group (that receives a single dose of PCV10 at 24 months). Participants are followed up to 24 months of age. The primary outcome is vaccine-type pneumococcal carriage at 24 months of age. Secondary outcomes are carriage at 6, 12 and 18 months of age and the comparative immunogenicity of the different schedules in terms of antibody responses, functional antibody responses and memory B cell responses.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Human Research Ethics Committee of the Royal Children's Hospital Melbourne and the Vietnam Ministry of Health Ethics Committee. The results, interpretation and conclusions will be presented to parents and guardians, at national and international conferences and published in peer-reviewed open access journals.

TRIAL REGISTRATION NUMBER

NCT03098628.

IMMUNOGENICITY AND IMPACT ON NASOPHARYNGEAL CARRIAGE OF A SINGLE DOSE OF PCV10 GIVEN TO VIETNAMESE CHILDREN AT 18 MONTHS OF AGE

Background

This study investigated the immunogenicity and impact on nasopharyngeal carriage of a single dose of PCV10 given to 18-month-old Vietnamese children. This information is important for countries considering catch-up vaccination during PCV introduction and in the context of vaccination during humanitarian crises.

Methods

Two groups of PCV-naïve children within the Vietnam Pneumococcal Project received PCV10 (n=197) or no PCV (unvaccinated; n=199) at 18 months of age. Blood samples were collected at 18, 19, and 24 months of age, and nasopharyngeal swabs at 18 and 24 months of age. Immunogenicity was assessed by measuring serotype-specific IgG, opsonophagocytosis (OPA) and memory B cells (Bmem). Pneumococci were detected and quantified using real-time PCR and serotyped by microarray.

Findings

At 19 months of age, IgG and OPA responses were higher in the PCV10 group compared with the unvaccinated group for all PCV10 serotypes and cross-reactive serotypes 6A and 19A. This was sustained out to 24 months of age, at which point PCV10-type carriage was 60% lower in the PCV10 group than the unvaccinated group. Bmem levels increased between 18 and 24 months of age in the vaccinated group.

Interpretation

We demonstrate strong protective immune responses in vaccinees following a single dose of PCV10 at 18 months of age, and a potential impact on herd protection through a substantial reduction in vaccine-type carriage. A single dose of PCV10 in the second year of life could be considered as part of catch-up campaigns or in humanitarian crises to protect children at high-risk of pneumococcal disease.

Australia's Role in Pneumococcal and Human Papillomavirus Vaccine Evaluation in Asia-Pacific

Australian researchers have made substantial contributions to the field of vaccinology over many decades. Two examples of this contribution relate to pneumococcal vaccines and the human papillomavirus (HPV) vaccine, with a focus on improving access to these vaccines in low- and lower-middle-income countries (LLMICs). Many LLMICs considering introducing one or both of these vaccines into their National Immunisation Programs face significant barriers such as cost, logistics associated with vaccine delivery. These countries also often lack the resources and expertise to undertake the necessary studies to evaluate vaccine performance. This review summarizes the role of Australia in the development and/or evaluation of pneumococcal vaccines and the HPV vaccine, including the use of alternative vaccine strategies among countries situated in the Asia-Pacific region. The outcomes of these research programs have had significant global health impacts, highlighting the importance of these vaccines in preventing pneumococcal disease as well as HPV-associated diseases.