The Efficacy and Duration of Protection of Pneumococcal Conjugate Vaccines Against Nasopharyngeal Carriage: A Meta-regression Model

The durability of vaccine-induced protection: an overview

INTRODUCTION

Current vaccines vary widely in both their efficacy against infection and disease, and the durability of the efficacy. Some vaccines provide practically lifelong protection with a single dose, while others provide only limited protection following annual boosters. What variables make vaccine-induced immune responses last? Can breakthroughs in these factors and technologies help us produce vaccines with better protection and fewer doses? The durability of vaccine-induced protection is now a hot area in vaccinology research, especially after COVID-19 vaccines lost their luster. It has fueled discussion on the eventual utility of existing vaccines to society and bolstered the anti-vaxxer camp. To sustain public trust in vaccines, lasting vaccines must be developed.

AREAS COVERED

This review summarizes licensed vaccines' protection. It analyses immunological principles and vaccine and vaccinee parameters that determine longevity of antibodies. The review concludes with challenges and the way forward to improve vaccine durability.

EXPERT OPINION

Despite enormous advances, we still lack essential markers and reliable correlates of lasting protection. Most research has focused on humoral immune responses, but we must also focus on innate, mucosal, and cellular responses - their assessment, correlates, determinants, and novel adjuvants. Suitable vaccine designs and platforms for durable immunity must be found.

The potential of saliva as an accessible and sensitive sample type for the detection of respiratory pathogens and host immunity

Despite its prominence in early scientific records, the usefulness of saliva as a respiratory specimen has been de-emphasised over the past century. However, due to its low cost and reliance on specific supply chains and the non-invasive nature of its collection, its benefits over swab-based specimens are again becoming increasingly recognised. These benefits were highlighted over the course of the COVID-19 pandemic, where saliva emerged as a more practical, clinically non-inferior sample type for the detection of SARS-CoV-2 and saw numerous saliva-based diagnostic tests approved for clinical use. Looking forward, as saliva uniquely contains both respiratory secretions and immunological components, it has potentially wide applications, ranging from clinical diagnostics to post-vaccine disease burden and immunity surveillance. This Personal View seeks to summarise the existing evidence for the use of saliva in detecting respiratory pathogens, beyond SARS-CoV-2, as well as detailing methodological factors that can influence sample quality and thus, clinical utility.

Association of pneumococcal carriage in infants with the risk of carriage among their contacts in Nha Trang, Vietnam: A nested cross-sectional survey

BACKGROUND

Infants are at highest risk of pneumococcal disease. Their added protection through herd effects is a key part in the considerations on optimal pneumococcal vaccination strategies. Yet, little is currently known about the main transmission pathways to this vulnerable age group. Hence, this study investigates pneumococcal transmission routes to infants in the coastal city of Nha Trang, Vietnam.

METHODS AND FINDINGS

In October 2018, we conducted a nested cross-sectional contact and pneumococcal carriage survey in randomly selected 4- to 11-month-old infants across all 27 communes of Nha Trang. Bayesian logistic regression models were used to estimate age specific carriage prevalence in the population, a proxy for the probability that a contact of a given age could lead to pneumococcal exposure for the infant. We used another Bayesian logistic regression model to estimate the correlation between infant carriage and the probability that at least one of their reported contacts carried pneumococci, controlling for age and locality. In total, 1,583 infants between 4 and 13 months old participated, with 7,428 contacts reported. Few infants (5%, or 86 infants) attended day care, and carriage prevalence was 22% (353 infants). Most infants (61%, or 966 infants) had less than a 25% probability to have had close contact with a pneumococcal carrier on the surveyed day. Pneumococcal infection risk and contact behaviour were highly correlated: If adjusted for age and locality, the odds of an infant's carriage increased by 22% (95% confidence interval (CI): 15 to 29) per 10 percentage points increase in the probability to have had close contact with at least 1 pneumococcal carrier. Moreover, 2- to 6-year-old children contributed 51% (95% CI: 39 to 63) to the total direct pneumococcal exposure risks to infants in this setting. The main limitation of this study is that exposure risk was assessed indirectly by the age-dependent propensity for carriage of a contact and not by assessing carriage of such contacts directly.

CONCLUSIONS

In this study, we observed that cross-sectional contact and infection studies could help identify pneumococcal transmission routes and that preschool-age children may be the largest reservoir for pneumococcal transmission to infants in Nha Trang, Vietnam.

Indirect effects of 13-valent pneumococcal conjugate vaccine on pneumococcal carriage in children hospitalised with acute respiratory infection despite heterogeneous vaccine coverage: an observational study in Lao People's Democratic Republic

Introduction

Empiric data on indirect (herd) effects of pneumococcal conjugate vaccines (PCVs) in settings with low or heterogeneous PCV coverage are limited. The indirect effects of PCV, which benefits both vaccinated and non-vaccinated individuals, are mediated by reductions in vaccine-type (VT) carriage (a prerequisite for disease). The aim of this study among hospitalised children in Lao People’s Democratic Republic (Lao PDR) is to determine the effectiveness of a 13-valent PCV (PCV13) against VT pneumococcal nasopharyngeal carriage (direct effects) and the association between village-level PCV13 coverage and VT carriage (indirect effects).

Methods

Pneumococcal nasopharyngeal carriage surveillance commenced in December 2013, shortly after PCV13 introduction (October 2013). We recruited and swabbed children aged 2–59 months admitted to hospital with acute respiratory infection. Pneumococci were detected using lytA quantitative real-time PCR and serotyped using microarray. PCV13 status and village-level PCV13 coverage were determined using written immunisation records. Associations between both PCV13 status and village-level PCV13 coverage and VT carriage were calculated using generalised estimating equations, controlling for potential confounders.

Results

We enrolled 1423 participants and determined PCV13 coverage for 368 villages (269 863 children aged under 5 years). By 2017, median village-level vaccine coverage reached 37.5%, however, the IQR indicated wide variation among villages (24.1–56.4). Both receipt of PCV13 and the level of PCV13 coverage were independently associated with a reduced odds of VT carriage: adjusted PCV13 effectiveness was 38.1% (95% CI 4.1% to 60.0%; p=0.032); and for each per cent increase in PCV13 coverage, the estimated odds of VT carriage decreased by 1.1% (95% CI 0.0% to 2.2%; p=0.056). After adjustment, VT carriage decreased from 20.0% to 12.8% as PCV13 coverage increased from zero to 60% among under 5.

Conclusions

Despite marked heterogeneity in PCV13 coverage, we found evidence of indirect effects in Lao PDR. Individual vaccination with PCV13 was effective against VT carriage.

Vaccine strategies to reduce the burden of pneumococcal disease in HIV-infected adults in Africa

INTRODUCTION

Streptococcus pneumoniae is the leading cause of invasive bacterial disease, globally. Despite antiretroviral therapy, adults infected with human immunodeficiency virus (HIV) are also at high risk of pneumococcal carriage and disease. Pneumococcal conjugate vaccines (PCVs) provide effective protection against vaccine serotype (VT) carriage and disease in children, and have been introduced worldwide, including most HIV-affected low- and middle-income countries. Unlike high-income countries, the circulation of VT persists in the PCV era in some low-income countries and results in a continued high burden of pneumococcal disease in HIV-infected adults. Moreover, no routine vaccination that directly protects HIV-infected adults in such settings has been implemented.

AREAS COVERED

Nonsystematic review on the pneumococcal burden in HIV-infected adults and vaccine strategies to reduce this burden.

EXPERT OPINION

We propose and discuss the relative merit of changing the infant PCV program to use (1a) a two prime plus booster dose schedule, (1b) a two prime plus booster dose schedule with an additional booster dose at school entry, to directly vaccinate (2a) HIV-infected adults or vaccinating (2b) HIV-infected pregnant women for direct protection, with added indirect protection to the high-risk neonates. We identify key knowledge gaps for such an evaluation and propose strategies to overcome them.

Pneumococcal conjugate vaccine primes mucosal immune responses to pneumococcal polysaccharide vaccine booster in Papua New Guinean children

Introduction

Invasive pneumococcal disease remains a major cause of hospitalization and death in Papua New Guinean (PNG) children. We assessed mucosal IgA and IgG responses in PNG infants vaccinated with pneumococcal conjugate vaccine (PCV) followed by a pneumococcal polysaccharide vaccine (PPV) booster.

Methods

Infants received 7-valent PCV (7vPCV) in a 0–1–2 (neonatal) or 1–2-3-month (infant) schedule, or no 7vPCV (control). At age 9 months all children received 23-valent PPV (23vPPV). IgA and IgG to 7vPCV and non-7vPCV (1, 5, 7F, 19A) serotypes were measured in saliva collected at ages 1, 2, 3, 4, 9, 10 and 18 months (131 children, 917 samples). Correlations were studied between salivary and serum IgG at 4, 10 and 18 months.

Results

Salivary IgA and IgG responses overall declined in the first 9 months. Compared to non-7vPCV recipients, salivary IgA remained higher in 7vPCV recipients for serotypes 4 at 3 months, 6B at 3 months (neonatal), and 14 at 3 (neonatal), 4 and 9 months (infant); and for salivary IgG for serotypes 4 at 3, 4 and 9 months, 6B at 9 months, 14 at 4 (neonatal) and 9 months, 18C at 3, 4, and 9 (infant) months, and 23F at 4 months. Following 23vPPV, salivary 7vPCV-specific IgA and IgG increased in 7vPCV-vaccinated children but not in controls; and salivary IgA against non-PCV serotypes 5 and 7F increased in 7vPCV recipients and non-recipients. Salivary and serum IgG against 7vPCV-serotypes correlated in 7vPCV-vaccinated children at 4 and 10 months of age.

Conclusions

PCV may protect high-risk children against pneumococcal colonization and mucosal disease by inducing mucosal antibody responses and priming for mucosal immune memory that results in mucosal immune responses after booster PPV. Saliva can be a convenient alternative sample to serum to study PCV-induced systemic IgG responses.

Ten year public health impact of 13-valent pneumococcal conjugate vaccination in infants: A modelling analysis

Pneumococcal disease is a substantial contributor to illness and death in young children globally. The introduction of 7-valent pneumococcal conjugate vaccine (PCV7) in 2000 had a significant impact in preventing pneumococcal disease in both vaccinated children and unvaccinated individuals (through herd effect). A higher valent PCV13 replaced PCV7 in late 2009. This analysis was undertaken to assess how many cases and deaths have been averted over the last decade since PCV13 introduction. A model estimated the number of infants vaccinated annually with PCV13, as well as the number of cases and deaths of invasive pneumococcal disease, pneumococcal pneumonia, and acute otitis media cases averted. PCV13 vaccination was estimated to have prevented 175.2 million cases of all pneumococcal diseases and 624,904 deaths globally between 2010 and 2019. These results demonstrate the substantial public health impact of PCV13 and highlight the importance of increasing the global reach of PCV programs.

Impact of 13Valent Vaccine for Prevention of Pneumococcal Diseases in Children and Adults at Risk: Possible Scenarios in Campania Region

BACKGROUND

Pneumonias are the most frequent infectious diseases, characterized by a high prevalence especially among children and adults at risk. The socio-economic impact caused by Streptococcus pneumoniae is evaluated in terms of morbidity, death rate and hospitalizations.

OBJECTIVE

The aim of the study was to demonstrate the potential economic advantages by implementation of an active anti-pneumococcal 13-valent vaccine strategy in Campania region (Southern Italy) in two different categories of subjects, children (aged 0-12), and adults (aged 50- 79) at risk (hypertension, nephropathies, COPD and heart diseases).

METHODS

Vaccination costs were compared with costs necessary to treat avoidable diseases in the presence and absence of a vaccination program.

RESULTS

Offering anti-pneumococcal 13-valent vaccine to the paediatric population was quantified as saving one million euros for Italian national health service in two years. In addition, offering anti-pneumococcal vaccine to adults at risk would generate a return of around 29 million euros.

CONCLUSION

In both cases, offering anti-pneumococcal 13-valent vaccine was proven to be a helpful political health strategy, not only in consideration of a reduction of cases but also in view of the favourable economic impacts.

High residual carriage of vaccine-serotype Streptococcus pneumoniae after introduction of pneumococcal conjugate vaccine in Malawi

There are concerns that pneumococcal conjugate vaccines (PCVs) in sub-Saharan Africa sub-optimally interrupt Streptococcus pneumoniae vaccine-serotype (VT) carriage and transmission. Here we assess PCV carriage using rolling, prospective nasopharyngeal carriage surveys between 2015 and 2018, 3.6–7.1 years after Malawi’s 2011 PCV13 introduction. Carriage decay rate is analysed using non-linear regression. Despite evidence of reduction in VT carriage over the study period, there is high persistent residual carriage. This includes among PCV-vaccinated children 3–5-year-old (16.1% relative reduction from 19.9% to 16.7%); PCV-unvaccinated children 6–8-year-old (40.5% reduction from 26.4% to 15.7%); HIV-infected adults 18-40-years-old on antiretroviral therapy (41.4% reduction from 15.2% to 8.9%). VT carriage prevalence half-life is similar among PCV-vaccinated and PCV-unvaccinated children (3.26 and 3.34 years, respectively). Compared with high-income settings, there is high residual VT carriage 3.6–7.1 years after PCV introduction. Rigorous evaluation of strategies to augment vaccine-induced control of carriage, including alternative schedules and catch-up campaigns, is required.

Impact of pneumococcal conjugate vaccines (PCV) in controlling carriage needs to be evaluated to inform vaccine policy. Here, Swarthout et al. show in a prospective rolling cross-sectional study in Malawi a high residual prevalence of vaccine-serotype S. pneumoniae 7 years after PCV introduction.

Determinants of high residual post-PCV13 pneumococcal vaccine-type carriage in Blantyre, Malawi: a modelling study

BACKGROUND

In November 2011, Malawi introduced the 13-valent pneumococcal conjugate vaccine (PCV13) into the routine infant schedule. Four to 7 years after introduction (2015-2018), rolling prospective nasopharyngeal carriage surveys were performed in the city of Blantyre. Carriage of Streptococcus pneumoniae vaccine serotypes (VT) remained higher than reported in high-income countries, and impact was asymmetric across age groups.

METHODS

A dynamic transmission model was fit to survey data using a Bayesian Markov-chain Monte Carlo approach, to obtain insights into the determinants of post-PCV13 age-specific VT carriage.

RESULTS

Accumulation of naturally acquired immunity with age and age-specific transmission potential were both key to reproducing the observed data. VT carriage reduction peaked sequentially over time, earlier in younger and later in older age groups. Estimated vaccine efficacy (protection against carriage) was 66.87% (95% CI 50.49-82.26%), similar to previous estimates. Ten-year projected vaccine impact (VT carriage reduction) among 0-9 years old was lower than observed in other settings, at 76.23% (CI 95% 68.02-81.96%), with sensitivity analyses demonstrating this to be mainly driven by a high local force of infection.

CONCLUSIONS

There are both vaccine-related and host-related determinants of post-PCV13 pneumococcal VT transmission in Blantyre with vaccine impact determined by an age-specific, local force of infection. These findings are likely to be generalisable to other Sub-Saharan African countries in which PCV impact on carriage (and therefore herd protection) has been lower than desired, and have implications for the interpretation of post-PCV carriage studies and future vaccination programs.

Pneumococcal conjugate vaccine use during humanitarian crises

Streptococcus pneumoniae is a common human commensal that causes a sizeable part of the overall childhood mortality in low income settings. Populations affected by humanitarian crises are at especially high risk, because a multitude of risk factors that are enhanced during crises increase pneumococcal transmission and disease severity. Pneumococcal conjugate vaccines (PCVs) provide effective protection and have been introduced into the majority of routine childhood immunisation programmes globally, though several barriers have hitherto limited their uptake during humanitarian crises. When PCV coverage cannot be sustained during crises or when PCV has not been part of routine programmes, mass vaccination campaigns offer a quick acting and programmatically feasible bridging solution until services can be restored. However, we currently face a paucity of evidence on which to base the structure of such campaigns. We believe that, now that PCV can be procured at a substantially reduced price through the Humanitarian Mechanism, this lack of information is a remaining hurdle to PCV use in humanitarian crises. Considering the difficulties in conducting research in crises, we propose an evidence generation pathway consisting of primary data collection in combination with mathematical modelling followed by quasi-experimental evaluation of a PCV intervention, which can inform on optimal vaccination strategies that consider age targeting, dosing regimens and impact duration.

Using pneumococcal carriage studies to monitor vaccine impact in low- and middle-income countries

Pneumococcal disease is a leading cause of childhood mortality, globally. The pneumococcal conjugate vaccine (PCV) has been introduced to many countries worldwide. However there are few studies evaluating PCV impacts in low- and middle-income countries (LMIC) because measuring the impact of PCV on pneumococcal disease in LMICs is challenging. We review the role of pneumococcal carriage studies for the evaluation of PCVs in LMICs and discuss optimal methods for conducting these studies. Fifteen carriage studies from 13 LMICs quantified the effects of PCV on carriage, and identified replacement carriage serotypes in the post-PCV era. Ten studies reported on the indirect effects of PCV on carriage. Results can be used to inform cost-effectiveness evaluations, guide policy decisions on dosing and product, and monitor equity in program implementation. Critically, we highlight gaps in our understanding of serotype replacement disease in LMICs and identify priorities for research to address this gap.

Cost Effectiveness of Elderly Pneumococcal Vaccination in Presence of Higher-Valent Pneumococcal Conjugate Childhood Vaccination: Systematic Literature Review with Focus on Methods and Assumptions

BACKGROUND

Previous systematic reviews concluded that pneumococcal vaccination in the elderly was cost effective. However, recently published economic evaluations state that it may not be cost effective when children are vaccinated with higher-valent pneumococcal conjugate vaccines. The literature suggests that the outcomes of vaccination in the elderly are strongly influenced by the vaccine effectiveness (VE) against the vaccine-type pneumococcal diseases (PD) and the impact of childhood vaccination on the vaccine-type PD incidence in the elderly, but the extent remains unclear.

METHODS

We conducted a systematic literature search of cost-effectiveness studies on vaccination in the elderly in the PubMed database starting from 2006. We included studies that consider the presence of a childhood vaccination with pneumococcal conjugate vaccine (PCV) 10 and PCV13. We focus on methods and assumptions used in modeling VE and epidemiology of PD over time.

RESULTS

Twenty-eight economic evaluations underwent full-text review and data extraction. Thirteen were selected for quality assessment. The studies with a higher quality score provide evidence that vaccinating the elderly with PCV13 is not cost effective, when an ongoing rapid decline in the incidence of PCV13-type PD is modeled. A moderate persistence of PCV13 serotypes, in particular due to PCV10 childhood vaccination, makes vaccination of the elderly with PCV13 more attractive. There is no agreement that combining PCV13 with polysaccharide vaccine PPSV23 is cost effective. PPSV23 is attractive when it is effective against non-invasive PD.

CONCLUSION

Methodological approaches and assumptions in modeling VE and the indirect effects of childhood vaccination have a major impact on outcomes of decision-analytic models and cost-effectiveness estimates. Considering recently observed trends in the epidemiology of pneumococcal serotypes, there is currently inconclusive evidence regarding the cost effectiveness of pneumococcal vaccination of the elderly due to lack of studies that model key serotypes such as serotype 3 separately from other groups of serotypes.

Estimated impact of revising the 13-valent pneumococcal conjugate vaccine schedule from 2+1 to 1+1 in England and Wales: A modelling study

BACKGROUND

In October 2017, the United Kingdom Joint Committee on Vaccination and Immunisation (JCVI) recommended removal of one primary dose of the 13-valent pneumococcal conjugate vaccine (PCV13) from the existing 2+1 schedule (2, 4, 12 months). We conducted a mathematical modelling study to investigate the potential impact of a 1+1 (3, 12 month) schedule on invasive pneumococcal disease (IPD) and pneumococcal community-acquired pneumonia (CAP). Our results and those from a 1+1 immunogenicity study formed the key evidence reviewed by JCVI.

METHODS AND FINDINGS

We developed age-structured, dynamic, deterministic models of pneumococcal transmission in England and Wales to describe the impact on IPD of 7-valent PCV (PCV7; introduced in 2006) and PCV13 (introduced in 2010). Key transmission and vaccine parameters were estimated by fitting to carriage data from 2001/2002 and post-PCV IPD data to 2015, using vaccine coverage, mixing patterns between ages, and population data. We considered various models to investigate potential reasons for the rapid increase in non-PCV13 (non-vaccine serotype [NVT]) IPD cases since 2014. After searching a large parameter space, 500 parameter sets were identified with a likelihood statistically close to the maximum and these used to predict future cases (median, prediction range from 500 parameter sets). Our findings indicated that the emergence of individual NVTs with higher virulence resulting from ongoing replacement was likely responsible; the NVT increase was predicted to plateau from 2020. Long-term simulation results suggest that changing to a 1+1 schedule would have little overall impact, as the small increase in vaccine-type IPD would be offset by a reduction in NVT IPD. Our results were robust to changes in vaccine assumptions in a sensitivity analysis. Under the base case scenario, a change to a 1+1 schedule in 2018 was predicted to produce 31 (6, 76) additional IPD cases over five years and 83 (-10, 242) additional pneumococcal-CAP cases, with together 8 (-2, 24) additional deaths, none in children under 15 years. Long-term continuation with the 2+1 schedule, or changing to a 1+1, was predicted to sustain current reductions in IPD cases in under-64-year-olds, but cases in 65+-year-olds would continue to increase because of the effects of an aging population. Limitations of our model include difficulty in fitting to past trends in NVT IPD in some age groups and inherent uncertainty about future NVT behaviour, sparse data for defining the mixing matrix in 65+-year-olds, and the methodological challenge of defining uncertainty on predictions.

CONCLUSIONS

Our findings suggest that, with the current mature status of the PCV programme in England and Wales, removing one primary dose in the first year of life would have little impact on IPD or pneumococcal CAP cases or associated deaths at any age. A reduction in the number of priming doses would improve programmatic efficiency and facilitate the introduction of new vaccines by reducing the number of coadministered vaccines given at 2 and 4 months of age in the current UK schedule. Our findings should not be applied to other settings with different pneumococcal epidemiology or with immature programmes and poor herd immunity.

Why is the rate of pneumococcal pneumonia declining?

PURPOSE OF REVIEW

As Streptococcus pneumoniae was considered the etiological agent of nearly all the cases of pneumonia at the beginning of the 20th century, and today is identified in fewer than 10-15% of cases, we analyze the possible causes of such a decline.

RECENT FINDINGS

Extensive use of early empiric antimicrobial therapy, discovery of previously unrecognized pathogens, availability to newer diagnostic methods for the recognition of the pneumonia pathogens (PCR, urinary antigens, monoclonal antibodies etc.) and of improved preventive measures, including vaccines, are some of possible explanations of the declining role of S. pneumoniae in the cause of pneumonia.

SUMMARY

The 14-valent and the 23-valent capsular polysaccharide pneumococcal vaccines were licensed in 1977 and 1983, respectively. The seven-valent protein-conjugated capsular polysaccharide vaccine, approved for routine use in children starting at 2 months of age, was highly effective in preventing invasive pneumococcal disease in children but also in adults because of the herd effect. In 2010, the 13-valent protein-conjugated capsular polysaccharide vaccine replaced seven-valent protein-conjugated capsular polysaccharide vaccine. With the use of conjugated vaccines, a decrease of the vaccine-type invasive pneumococcal disease for all age groups was observed. Both the direct effect of the vaccine and the so-called herd immunity are considered responsible for much of the decline.

Immunogenicity and Immune Memory after a Pneumococcal Polysaccharide Vaccine Booster in a High-Risk Population Primed with 10-Valent or 13-Valent Pneumococcal Conjugate Vaccine: A Randomized Controlled Trial in Papua New Guinean Children

We investigated the immunogenicity, seroprotection rates and persistence of immune memory in young children at high risk of pneumococcal disease in Papua New Guinea (PNG). Children were primed with 10-valent (PCV10) or 13-valent pneumococcal conjugate vaccines (PCV13) at 1, 2 and 3 months of age and randomized at 9 months to receive PPV (PCV10/PPV-vaccinated, n = 51; PCV13/PPV-vaccinated, n = 52) or no PPV (PCV10/PPV-naive, n = 57; PCV13/PPV-naive, n = 48). All children received a micro-dose of PPV at 23 months of age to study the capacity to respond to a pneumococcal challenge. PPV vaccination resulted in significantly increased IgG responses (1.4 to 10.5-fold change) at 10 months of age for all PPV-serotypes tested. Both PPV-vaccinated and PPV-naive children responded to the 23-month challenge and post-challenge seroprotection rates (IgG ≥ 0.35 μg/mL) were similar in the two groups (80⁻100% for 12 of 14 tested vaccine serotypes). These findings show that PPV is immunogenic in 9-month-old children at high risk of pneumococcal infections and does not affect the capacity to produce protective immune responses. Priming with currently available PCVs followed by a PPV booster in later infancy could offer improved protection to young children at high risk of severe pneumococcal infections caused by a broad range of serotypes.

Association Between the Decline in Pneumococcal Disease in Unimmunized Adults and Vaccine-Derived Protection Against Colonization in Toddlers and Preschool-Aged Children

Vaccinating children with pneumococcal conjugate vaccine (PCV) disrupts transmission, reducing disease rates in unvaccinated adults. When considering changes in vaccine dosing strategies (e.g., removing doses), it is critical to understand which groups of children contribute most to transmission to adults. We used data from Israel (2009–2016) to evaluate how the buildup of vaccine-associated immunity in children was associated with declines in invasive pneumococcal disease (IPD) due to vaccine-targeted serotypes in unimmunized adults. Data on vaccine uptake and prevalence of colonization with PCV-targeted serotypes were obtained from children visiting an emergency department in southern Israel and from surveys of colonization from central Israel. Data on IPD in adults were obtained from a nationwide surveillance study carried out in Israel. We compared the trajectory of decline of IPD due to PCV-targeted serotypes in adults with the decline of colonization prevalence and increase in vaccine-derived protection against pneumococcal carriage among different age groupings of children. The declines in IPD in adults were most closely associated with the declines in colonization and increased vaccination coverage among children in the age range of 36–59 months. This suggests that preschool-aged children, rather than infants, are responsible for maintaining the indirect benefits of PCVs.

Exploring the role of competition induced by non-vaccine serotypes for herd protection following pneumococcal vaccination

The competitive pressure from non-vaccine serotypes may have helped pneumococcal conjugate vaccines (PCVs) to limit vaccine-type (VT) serotype prevalence. We aimed to investigate if, consequently, the indirect protection of vaccines targeting most pneumococcal serotypes could fall short of the profound effects of current formulations. We compared three previously described pneumococcal models harmonized to simulate 20 serotypes with a combined pre-vaccination prevalence in children younger than 5-years-old of 40%. We simulated vaccines of increasing valency by adding serotypes in order of their competitiveness and explored their ability to reduce VT carriage by 95% within 10 years after introduction. All models predicted that additional valency will reduce indirect vaccine effects and hence the overall vaccine impact on carriage both in children and adults. Consequently, the minimal effective coverage (efficacy against carriage×vaccine coverage) needed to eliminate VT carriage increased with increasing valency. One model predicted this effect to be modest, while the other two predicted that high-valency vaccines may struggle to eliminate VT pneumococci unless vaccine efficacy against carriage can be substantially improved. Similar results were obtained when settings of higher transmission intensity and different PCV formulations were explored. Failure to eliminate carriage as a result of increased valency could lead to overall decreased impact of vaccination if the disease burden caused by the added serotypes is low. Hence, a comparison of vaccine formulations of varying valency, and pan-valent formulations in particular, should consider the invasiveness of targeted serotypes, as well as efficacy against carriage.

Predicting the impact of pneumococcal conjugate vaccine programme options in Vietnam

Although catch-up campaigns (CCs) at the introduction of pneumococcal conjugate vaccines (PCVs) may accelerate their impact, supply constraints may limit their benefit if the need for additional PCV doses results in introduction delay. We studied the impact of PCV13 introduction with and without CC in Nha Trang, Vietnam – a country that has not yet introduced PCV – through a dynamic transmission model. We modelled the impact on carriage and invasive pneumococcal disease (IPD) of routine vaccination (RV) only and that of RV with CCs targeting <1y olds (CC1), <2y olds (CC2) and <5y olds (CC5). The model was fitted to nasopharyngeal carriage data, and post-PCV predictions were based on best estimates of parameters governing post-PCV dynamics. With RV only, elimination in carriage of vaccine-type (VT) serotypes is predicted to occur across all age groups within 10 years after introduction, with near-complete replacement by non-VT. Most of the benefit of CCs is predicted to occur within the first 3 years with the highest impact at one year, when IPD incidence is predicted to be 11% (95%CrI 9 – 14%) lower than RV with CC1, 25% (21 – 30 %) lower with CC2 and 38% (32 – 46%) lower with CC5. However, CCs would only prevent more cases of IPD insofar as such campaigns do not delay introduction by more than about 6, 12 and 18 months for CC1, CC2 and CC5. Those findings are important to help guide vaccine introduction in countries that have not yet introduced PCV, particularly in Asia.

A Cost-Effectiveness Analysis of the 10-Valent Pneumococcal Non-Typeable Haemophilus influenzae Protein D Conjugate Vaccine (PHiD-CV) Compared to the 13-Valent Pneumococcal Conjugate Vaccine (PCV13) for Universal Mass Vaccination Implementation in New Zealand

OBJECTIVES

Invasive pneumococcal disease (IPD), pneumonia and acute otitis media (AOM) still represent a significant medical burden in children < 5 years of age in New Zealand (NZ), with marked disparities across socio-economic and ethnic groups. This cost-effectiveness evaluation aims to compare the potential impact of two childhood universal immunisation strategies: vaccination with a 3 + 1 schedule of the 10-valent pneumococcal non-typeable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV, Synflorix, GSK) and the 13-valent pneumococcal conjugate vaccine (PCV13, Prevenar 13, Pfizer).

METHODS

A static Markov-process cohort model was used to simulate the epidemiological and economic burden of pneumococcal diseases on a single-birth cohort over its lifetime. Costs and outcomes were discounted annually at 3.5%. Epidemiological and cost inputs were extracted from the most recently available NZ data, or derived from the most relevant reference countries' sources. The most updated evidence on the efficacies of the corresponding vaccines were used, particularly the significant effectiveness for PHiD-CV against IPD caused by serotype 19A.

RESULTS

The model estimated that both vaccines have a broadly comparable impact on IPD-related diseases and pneumonia. Due to the additional benefits possible through broader impact on AOM, PHiD-CV is estimated to potentially provide additional discounted cost offsets of approximately NZD 0.8 million over the lifetime of the birth cohort.

CONCLUSIONS

To ensure health equity in children, given the substantial burden of pneumonia and AOM, decision-makers should also take into account the impact of PCVs on these diseases for decisions relating to routine infant immunization.

GSK STUDY IDENTIFIER

HO-15-16775.

Adult pneumococcal vaccination: advances, impact, and unmet needs

PURPOSE OF REVIEW

Preventing pneumonia in the elderly and individuals with comorbidities is an unmet clinical need. Streptococcus pneumoniae is the commonest bacterial cause of pneumonia, and we summarize recent findings regarding current S. pneumoniae vaccines, and debate their efficacy and cost-effectiveness in risk groups. We also discuss potential future vaccine strategies such as protein antigen vaccines.

RECENT FINDINGS

Current vaccination with pneumococcal polysaccharide vaccine does not prevent S. pneumoniae pneumonia. Vaccination with pneumococcal conjugated vaccine (PCV) prevents nasopharyngeal colonization, but although PCV13 has recently been shown to prevent S. pneumoniae pneumonia in adults, its overall efficacy was relatively low. The results of cost-effectiveness studies of PCV vaccination in adults are variable with some showing this is a cost-effective strategy, whereas others have not. The lack of cost-effectiveness is predominantly because of the current cost of the PCV vaccine and the existing herd immunity effect from childhood PCV vaccination on vaccine serotypes.

SUMMARY

S. pneumoniae pneumonia is a vaccine-preventable disease but remains a common cause of morbidity and mortality. Advances in vaccination using approaches that induce serotypes-independent immunity and are immunogenic in high-risk groups are required to reduce the burden of disease because of S. pneumoniae.

Re-emergence of pneumococcal colonization by vaccine serotype 19F in persons aged ≥5 years after 13-valent pneumococcal conjugate vaccine introduction-Alaska, 2008-2013

BACKGROUND

The pneumococcal conjugate vaccine (PCV) was introduced in 2001. Widespread PCV use nearly eradicated pneumococcal colonization by vaccine serotypes. Since 2008, however, colonization by PCV-serotype 19F has increased in Alaska residents. We describe the epidemiology of re-emerging serotype 19F colonization.

METHODS

We conducted annual cross-sectional colonization surveys from 2008 to 2013. We recruited children aged <5 years at 2 urban clinics and participants of all ages from Region-A (2 villages), Region-B (4 villages), and Region-C (2 villages). We interviewed participants and reviewed their medical records to obtain demographic information and determine PCV status. We obtained nasopharyngeal swab specimens from participants to identify pneumococci and to determine the pneumococcal serotype, antimicrobial resistance, and multilocus sequence type. We used the Cochran-Armitage test to assess for significant trends in colonization across time periods.

RESULTS

Among participants aged <5 years, pneumococcal serotype 19F colonization remained unchanged from 2008-2009 (0.7%) to 2012-2013 (0.5%; P-value [P] = .54). Serotype 19F colonization increased from 2008-2009 to 2012-2013 among participants aged 5-11 years (0.3% to 3.2%; P < .01), participants 12-17 years (0.0% to 2.0%; P < .01), and participants aged ≥18 years (0.1% to 0.5%; P < .01). During 2012-2013, 85 (93%) of 91 pneumococcal serotype 19F isolates were identified among participants from Region B; the majority of serotype 19F isolates belonged to an antimicrobial nonsusceptibility pattern corresponding to a novel multilocus sequence type 9074.

CONCLUSIONS

PCV continues to protect against serotype 19F colonization in vaccinated children aged <5 years. The direct PCV impact on serotype 19F colonization in persons aged 5-11 years and indirect impact in persons aged ≥12 years is waning, possibly because of a newly introduced genotype in Region-B.

Immunization, Antibiotic Use, and Pneumococcal Colonization Over a 15-Year Period

BACKGROUND

Rates of invasive pneumococcal disease have declined since widespread introduction of pneumococcal conjugate vaccines (PCVs) in the United States. We evaluated the impact of immunization status and recent antibiotic use on an individual child's risk of colonization.

METHODS

This study extends previously reported data from children <7 years of age seen for well child or acute care visits in Massachusetts communities. Nasopharyngeal swabs were collected during 6 surveillance seasons from 2000 to 2014. Parent surveys and medical record reviews confirmed immunization status and recent antibiotic use. We estimated the proportions of children colonized with PCV7-included, additional PCV13-included, and non-PCV13 serotypes. Risk factors for colonization with additional PCV13-included and non-PCV13 serotypes were assessed by using generalized linear mixed models adjusted for clustering by community.

RESULTS

Among 6537 children, 19A emerged as the predominant serotype in 2004, with substantial reductions in 2014. Among non-PCV serotypes, 15B/C, 35B, 23B, 11A, and 23A were most common in 2014. We observed greater odds for both additional PCV13 and non-PCV13 colonization in younger children, those with more child care exposure, and those with a concomitant respiratory tract infection. Adjusted odds for additional PCV13 colonization was lower (odds ratio 0.48 [95% confidence interval 0.31-0.75]) among children up-to-date for PCV13 vaccines. Recent antibiotic use was associated with higher odds of additional PCV13 colonization but substantially lower odds of non-PCV13 colonization.

CONCLUSIONS

Despite the success of pneumococcal vaccines in reducing colonization and disease due to targeted serotypes, ongoing community-based surveillance will be critical to evaluate the impact of interventions on pneumococcal colonization and disease.

Pneumococcal responses are similar in Papua New Guinean children aged 3-5 years vaccinated in infancy with pneumococcal polysaccharide vaccine with or without prior pneumococcal conjugate vaccine, or without pneumococcal vaccination

Trial design

In an earlier trial, Papua New Guinean (PNG) children at high risk of pneumococcal disease were randomized to receive 0 or 3 doses of 7-valent pneumococcal conjugate vaccine (PCV7), followed by a single dose of 23-valent pneumococcal polysaccharide vaccine (PPV23) at 9 months of age. We here studied in a non-randomized follow-up trial the persistence of pneumococcal immunity in these children at 3–5 years of age (n = 132), and in 121 community controls of a similar age with no prior pneumococcal vaccination.

Methods

Circulating IgG antibody titers to all PCV7 and PPV23-only serotypes 2, 5 and 7F were measured before and after challenge with 1/5^th of a normal PPV23 dose. Serotype-specific memory B-cells were enumerated at 10 months and 3–5 years of age for a subgroup of study children.

Results

Serotype-specific IgG antibody titers before and after challenge were similar for children who received PCV7/PPV23, PPV23 only, or no pneumococcal vaccines. Before challenge, at least 89% and 59% of children in all groups had serotype-specific titers ≥ 0.35μg/ml and ≥ 1.0 μg/ml, respectively. Post-challenge antibody titers were higher or similar to pre-challenge titers for most children independent of pneumococcal vaccination history. The rise in antibody titers was significantly lower when pre-challenge titers were higher. Overall the relative number of serotype-specific memory B-cells remained the same or increased between 10 months and 3–5 years of age, and there were no differences in serotype-specific memory B-cell numbers at 3–5 years of age between the three groups.

Conclusions

Immunity induced by PCV7 and/or PPV23 immunization in infancy does not exceed that of naturally acquired immunity in 3-5-year-old children living in a highly endemic area. Also, there was no evidence that PPV23 immunization in the first year of life following PCV7 priming induces longer-term hypo-responsiveness.

Trial registration

Clinicaltrials.gov NCT01414504 and NCT00219401.

Imputing the Direct and Indirect Effectiveness of Childhood Pneumococcal Conjugate Vaccine Against Invasive Pneumococcal Disease by Surveying Temporal Changes in Nasopharyngeal Pneumococcal Colonization

The limited capability in most low- to middle-income countries to study the benefit of pneumococcal conjugate vaccine (PCV) in protecting against invasive pneumococcal disease (IPD) calls for alternate strategies to assess this. We used a mathematical model to predict the direct and indirect effectiveness of PCV by analyzing serotype-specific colonization prevalence and IPD incidence prior to and following childhood PCV immunization in South Africa. We analyzed IPD incidence from 2005 to 2012 and colonization studies undertaken in human immunodeficiency virus (HIV)-uninfected and HIV-infected child-mother dyads from 2007 to 2009 (pre-PCV era), in 2010 (7-valent PCV era), and in 2012 (13-valent PCV era). We compared the model-predicted changes in IPD incidence with observed changes in IPD incidence, according to HIV status, in children aged 3 months-5 years and in women aged 18-45 years. We observed reductions in vaccine-serotype colonization and IPD due to vaccine serotypes among children and women after PCV introduction. Using the changes in vaccine-serotype colonization data, the model-predicted changes in vaccine-serotype IPD incidence rates were similar to the observed changes in PCV-unvaccinated children and adults, but not among children under age 24 months. Surveillance of colonization prior to and following PCV use can be used to impute the indirect protection afforded by PCV in unvaccinated age groups, including those in high-HIV-prevalence settings.

Geographic variation in pneumococcal vaccine efficacy estimated from dynamic modeling of epidemiological data post-PCV7

Although mean efficacy of multivalent pneumococcus vaccines has been intensively studied, variance in vaccine efficacy (VE) has been overlooked. Different net individual protection across settings can be driven by environmental conditions, local serotype and clonal composition, as well as by socio-demographic and genetic host factors. Understanding efficacy variation has implications for population-level effectiveness and other eco-evolutionary feedbacks. Here I show that realized VE can vary across epidemiological settings, by applying a multi-site-one-model approach to data post-vaccination. I analyse serotype prevalence dynamics following PCV7, in asymptomatic carriage in children attending day care in Portugal, Norway, France, Greece, Hungary and Hong-Kong. Model fitting to each dataset provides site-specific estimates for vaccine efficacy against acquisition, and pneumococcal transmission parameters. According to this model, variable serotype replacement across sites can be explained through variable PCV7 efficacy, ranging from 40% in Norway to 10% in Hong-Kong. While the details of how this effect is achieved remain to be determined, here I report three factors negatively associated with the VE readout, including initial prevalence of serotype 19F, daily mean temperature, and the Gini index. The study warrants more attention on local modulators of vaccine performance and calls for predictive frameworks within and across populations.

Assessing the efficiency of catch-up campaigns for the introduction of pneumococcal conjugate vaccine: a modelling study based on data from PCV10 introduction in Kilifi, Kenya

BACKGROUND

The World Health Organisation recommends the use of catch-up campaigns as part of the introduction of pneumococcal conjugate vaccines (PCVs) to accelerate herd protection and hence PCV impact. The value of a catch-up campaign is a trade-off between the costs of vaccinating additional age groups and the benefit of additional direct and indirect protection. There is a paucity of observational data, particularly from low- and middle-income countries, to quantify the optimal breadth of such catch-up campaigns.

METHODS

In Kilifi, Kenya, PCV10 was introduced in 2011 using the three-dose Expanded Programme on Immunisation infant schedule and a catch-up campaign in children <5 years old. We fitted a transmission dynamic model to detailed local data, including nasopharyngeal carriage and invasive pneumococcal disease (IPD), to infer the marginal impact of the PCV catch-up campaign over hypothetical routine cohort vaccination in that setting and to estimate the likely impact of alternative campaigns and their dose efficiency.

RESULTS

We estimated that, within 10 years of introduction, the catch-up campaign among children <5 years old prevents an additional 65 (48-84) IPD cases across age groups, compared to PCV cohort introduction alone. Vaccination without any catch-up campaign prevented 155 (121-193) IPD cases and used 1321 (1058-1698) PCV doses per IPD case prevented. In the years after implementation, the PCV programme gradually accrues herd protection, and hence its dose efficiency increases: 10 years after the start of cohort vaccination alone the programme used 910 (732-1184) doses per IPD case averted. We estimated that a two-dose catch-up among children <1 year old uses an additional 910 (732-1184) doses per additional IPD case averted. Furthermore, by extending a single-dose catch-up campaign to children aged 1 to <2 years and subsequently to those aged 2 to <5 years, the campaign uses an additional 412 (296-606) and 543 (403-763) doses per additional IPD case averted. These results were not sensitive to vaccine coverage, serotype competition, the duration of vaccine protection or the relative protection of infants.

CONCLUSIONS

We find that catch-up campaigns are a highly dose-efficient way to accelerate population protection against pneumococcal disease.

Streptococcus pneumoniae colonisation in children and adolescents with asthma: impact of the heptavalent pneumococcal conjugate vaccine and evaluation of potential effect of thirteen-valent pneumococcal conjugate vaccine

Background

The main aim of this study was to evaluate Streptococcus pneumoniae carriage in a group of school-aged children and adolescents with asthma because these results might indicate the theoretical risk of invasive pneumococcal disease (IPD) of such patients and the potential protective efficacy of the 13-valent pneumococcal conjugate vaccine (PCV13).

Methods

Oropharyngeal samples were obtained from 423 children with documented asthma (300 males, 70.9 %), and tested for the autolysin-A-encoding (lytA) and the wzg (cpsA) gene of S. pneumoniae by means of real-time polymerase chain reaction.

Results

S. pneumoniae was identified in the swabs of 192 subjects (45.4 %): 48.4 % of whom were aged <10 years, 46.9 % aged 10–14 years, and 4.7 % aged ≥15 years (p < 0.001). Carriage was significantly less frequent among the children who had received recent antibiotic therapy (odds ratio [OR 0.41]; 95 % confidence interval [95 % CI] 0.22–0.76). Multivariate analyses showed no association between carriage and vaccination status, with ORs of 1.05 (95 % CI 0.70–1.58) for carriers of any pneumococcal serotype, 1.08 (95 % CI 0.72–1.62) for carriers of any of the serotypes included in 7-valent pneumococcal conjugate vaccine (PCV7), and 0.76 (95 % CI 0.45–1.28) for carriers of any of the six additional serotypes of PCV13. Serotypes 19 F, 4 and 9 V were the most frequently identified serotypes in vaccinated subjects.

Conclusions

These results showed that carriage of S. pneumoniae is relatively common in all school-aged children and adolescents with asthma, regardless of the severity of disease and the administration of PCV7 in the first years of life. This highlights the problem of the duration of the protection against colonisation provided by pneumococcal conjugate vaccine, and the importance of re-colonization by the same pneumococcal serotypes included in the previously used vaccine.