Modelling the immunological response to a tetravalent dengue vaccine from multiple phase-2 trials in Latin America and South East Asia

Regional Variation of the CD4 and CD8 T Cell Epitopes Conserved in Circulating Dengue Viruses and Shared with Potential Vaccine Candidates

As dengue expands globally and many vaccines are under trials, there is a growing recognition of the need for assessing T cell immunity in addition to assessing the functions of neutralizing antibodies during these endeavors. While several dengue-specific experimentally validated T cell epitopes are known, less is understood about which of these epitopes are conserved among circulating dengue viruses and also shared by potential vaccine candidates. As India emerges as the epicenter of the dengue disease burden and vaccine trials commence in this region, we have here aligned known dengue specific T cell epitopes, reported from other parts of the world with published polyprotein sequences of 107 dengue virus isolates available from India. Of the 1305 CD4 and 584 CD8 epitopes, we found that 24% and 41%, respectively, were conserved universally, whereas 27% and 13% were absent in any viral isolates. With these data, we catalogued epitopes conserved in circulating dengue viruses from India and matched them with each of the six vaccine candidates under consideration (TV003, TDEN, DPIV, CYD-TDV, DENVax and TVDV). Similar analyses with viruses from Thailand, Brazil and Mexico revealed regional overlaps and variations in these patterns. Thus, our study provides detailed and nuanced insights into regional variation that should be considered for itemization of T cell responses during dengue natural infection and vaccine design, testing and evaluation.

Dengue overview: An updated systemic review

Dengue is caused by the dengue virus (DENVs) infection and clinical manifestations include dengue fever (DF), dengue hemorrhagic fever (DHF), or dengue shock syndrome (DSS). Due to a lack of antiviral drugs and effective vaccines, several therapeutic and control strategies have been proposed. A systemic literature review was conducted according to PRISMA guidelines to select proper references to give an overview of DENV infection. Results indicate that understanding the virus characteristics and epidemiology are essential to gain the basic and clinical knowledge as well as dengue disseminated pattern and status. Different factors and mechanisms are thought to be involved in the presentation of DHF and DSS, including antibody-dependent enhancement, immune dysregulation, viral virulence, host genetic susceptibility, and preexisting dengue antibodies. This study suggests that dissecting pathogenesis and risk factors as well as developing different types of therapeutic and control strategies against DENV infection are urgently needed.

Dengue virus infection - a review of pathogenesis, vaccines, diagnosis and therapy

The transmission of dengue virus (DENV) from an infected Aedes mosquito to a human, causes illness ranging from mild dengue fever to fatal dengue shock syndrome. The similar conserved structure and sequence among distinct DENV serotypes or different flaviviruses has resulted in the occurrence of cross reaction followed by antibody-dependent enhancement (ADE). Thus far, the vaccine which can provide effective protection against infection by different DENV serotypes remains the biggest hurdle to overcome. Therefore, deep investigation is crucial for the potent and effective therapeutic drugs development. In addition, the cross-reactivity of flaviviruses that leads to false diagnosis in clinical settings could result to delay proper intervention management. Thus, the accurate diagnostic with high specificity and sensitivity is highly required to provide prompt diagnosis in respect to render early treatment for DENV infected individuals. In this review, the recent development of neutralizing antibodies, antiviral agents, and vaccine candidates in therapeutic platform for DENV infection will be discussed. Moreover, the discovery of antigenic cryptic epitopes, principle of molecular mimicry, and application of single-chain or single-domain antibodies towards DENV will also be presented.

Dengvaxia: the world's first vaccine for prevention of secondary dengue

The objective of this manuscript was to review and evaluate the efficacy and safety data of Dengvaxia for the treatment of severe secondary dengue infection. Dengvaxia is the brand name for chimeric yellow fever-dengue-tetravalent dengue vaccine (CYD-TDV). A literature search through PubMed was conducted using the keywords ‘dengue vaccine’, ‘Dengvaxia’, ‘efficacy’ or ‘safety’. Trials were selected if they appropriately assessed vaccine efficacy or were related to the vaccine approval process for CYD-TDV. Findings from this review underline the evolution of vaccine efficacy against seroprevalence, serotypes, and various ages. There are currently no preventive measures or antiviral treatments for dengue; CYD-TDV is the first vaccine to receive US Food and Drug Administration approval. Protective responses seen with the complete administration of CYD-TDV can become a standardized tool as part of a world vaccination program.

Functional Profiling of Antibody Immune Repertoires in Convalescent Zika Virus Disease Patients

The re-emergence of Zika virus (ZIKV) caused widespread infections that were linked to Guillain-Barré syndrome in adults and congenital malformation in fetuses, and epidemiological data suggest that ZIKV infection can induce protective antibody responses. A more detailed understanding of anti-ZIKV antibody responses may lead to enhanced antibody discovery and improved vaccine designs against ZIKV and related flaviviruses. Here, we applied recently-invented library-scale antibody screening technologies to determine comprehensive functional molecular and genetic profiles of naturally elicited human anti-ZIKV antibodies in three convalescent individuals. We leveraged natively paired antibody yeast display and NGS to predict antibody cross-reactivities and coarse-grain antibody affinities, to perform in-depth immune profiling of IgM, IgG, and IgA antibody repertoires in peripheral blood, and to reveal virus maturation state-dependent antibody interactions. Repertoire-scale comparison of ZIKV VLP-specific and non-specific antibodies in the same individuals also showed that mean antibody somatic hypermutation levels were substantially influenced by donor-intrinsic characteristics. These data provide insights into antiviral antibody responses to ZIKV disease and outline systems-level strategies to track human antibody immune responses to emergent viral infections.

The first licensed dengue vaccine: can it be used in travelers?

PURPOSE OF REVIEW

The first dengue vaccine (Dengvaxia) was endorsed by the European Medicine Agency and the US Food and Drug Administration. Given the excess risk of severe dengue in seronegative vaccinees, use is restricted to seropositive individuals. Dengvaxia confers high protection against severe dengue in seropositive vaccinees.

RECENT FINDINGS

With increasing global travel, the probability of travelers being seropositive increases. Such seropositive travelers may be at increased risk of severe dengue as a result of a second dengue infection during repeat travel. Nevertheless, the use of Dengvaxia in travelers requires a careful analysis of all the factors. Seropositive travelers only present a minority of all travelers. A validated rapid diagnostic test to screen for dengue serostatus is not yet available. Such a test should be highly specific to avoid inadvertent vaccination of seronegative individuals. The three-dose regimen precludes the use in most travelers who tend to present at travel clinics less than 6 weeks prior to departure. Furthermore, questions about potential sub-optimal immunogenicity in seropositives in nonendemic settings, and the need and timing of boosters remain unanswered.

SUMMARY

Although there could potentially be substantial protection against severe dengue in seropositive travelers, Dengvaxia is far from an ideal travel vaccine.

Challenges in Dengue Vaccines Development: Pre-existing Infections and Cross-Reactivity

Dengue is one of the most frequently transmitted mosquito-borne diseases in the world, which creates a significant public health concern globally, especially in tropical and subtropical countries. It is estimated that more than 390 million people are infected with dengue virus each year and around 96 million develop clinical pathologies. Dengue infections are not only a health problem but also a substantial economic burden. To date, there are no effective antiviral therapies and there is only one licensed dengue vaccine that only demonstrated protection in the seropositive (Immune), naturally infected with dengue, but not dengue seronegative (Naïve) vaccines. In this review, we address several immune components and their interplay with the dengue virus. Additionally, we summarize the literature pertaining to current dengue vaccine development and advances. Moreover, we review some of the factors affecting vaccine responses, such as the pre-vaccination environment, and provide an overview of the significant challenges that face the development of an efficient/protective dengue vaccine including the presence of multiple serotypes, antibody-dependent enhancement (ADE), as well as cross-reactivity with other flaviviruses. Finally, we discuss targeting T follicular helper cells (Tfh), a significant cell population that is essential for the production of high-affinity antibodies, which might be one of the elements needed to be specifically targeted to enhance vaccine precision to dengue regardless of dengue serostatus.

Modelling the Use of Vaccine and Wolbachia on Dengue Transmission Dynamics

The use of vaccine and Wolbachia has been proposed as strategies against dengue. Research showed that the Wolbachia intervention is highly effective in areas with low to moderate transmission levels. On the other hand, the use of vaccine is strongly effective when it is implemented on seropositive individuals and areas with high transmission levels. The question that arises is could the combination of both strategies result in higher reduction in the number of dengue cases? This paper seeks to answer the aforementioned question by the use of a mathematical model. A deterministic model in the presence of vaccine and Wolbachia has been developed and analysed. Numerical simulations were presented and public health implications were discussed. The results showed that the performance of Wolbachia in reducing the number of dengue cases is better than that of vaccination if the vaccine efficacy is low, otherwise, the use of vaccine is sufficient to reduce dengue incidence and hence the combination of Wolbachia and vaccine is not necessary.

A Review on Dengue Vaccine Development

Dengue virus (DENV) has become a global health threat with about half of the world's population at risk of infection. Although the disease caused by DENV is self-limiting in the first infection, the antibody-dependent enhancement (ADE) effect increases the mortality in the second infection with a heterotypic virus. Since there is no specific efficient medicine in treatment, it is urgent to develop vaccines to prevent infection and disease progression. Currently, only a live attenuated vaccine, chimeric yellow fever 17D-tetravalent dengue vaccine (CYD-TDV), has been licensed for clinical use in some countries, and many candidate vaccines are still under research and development. This review discusses the progress, strengths, and weaknesses of the five types of vaccines including live attenuated vaccine, inactivated virus vaccine, recombinant subunit vaccine, viral vectored vaccine, and DNA vaccine.

Using cluster analysis to reconstruct dengue exposure patterns from cross-sectional serological studies in Singapore

Background

Dengue is a mosquito-borne viral disease caused by one of four serotypes (DENV1-4). Infection provides long-term homologous immunity against reinfection with the same serotype. Plaque reduction neutralization test (PRNT) is the gold standard to assess serotype-specific antibody levels. We analysed serotype-specific antibody levels obtained by PRNT in two serological surveys conducted in Singapore in 2009 and 2013 using cluster analysis, a machine learning technique that was used to identify the most common histories of DENV exposure.

Methods

We explored the use of five distinct clustering methods (i.e. agglomerative hierarchical, divisive hierarchical, K-means, K-medoids and model-based clustering) with varying number (from 4 to 10) of clusters for each method. Weighted rank aggregation, an evaluating technique for a set of internal validity metrics, was adopted to determine the optimal algorithm, comprising the optimal clustering method and the optimal number of clusters.

Results

The K-means algorithm with six clusters was selected as the algorithm with the highest weighted rank aggregation. The six clusters were characterised by (i) dominant DENV2 PRNT titres; (ii) co-dominant DENV1 and DENV2 titres with average DENV2 titre > average DENV1 titre; (iii) co-dominant DENV1 and DENV2 titres with average DENV1 titre > average DENV2 titre; (iv) low PRNT titres against DENV1-4; (v) intermediate PRNT titres against DENV1-4; and (vi) dominant DENV1-3 titres. Analyses of the relative size and age-stratification of the clusters by year of sample collection and the application of cluster analysis to the 2009 and 2013 datasets considered separately revealed the epidemic circulation of DENV2 and DENV3 between 2009 and 2013.

Conclusion

Cluster analysis is an unsupervised machine learning technique that can be applied to analyse PRNT antibody titres (without pre-established cut-off thresholds to indicate protection) to explore common patterns of DENV infection and infer the likely history of dengue exposure in a population.

A review of Dengvaxia®: development to deployment

Dengue is the world's most prevalent and important arboviral disease. More than 50% of the world's population lives at daily risk of infection and it is estimated more than 95 million people a year seek medical care following infection. Severe disease can manifest as plasma leakage and potential for clinically significant hemorrhage, shock, and death. Treatment is supportive and there is currently no licensed anti-dengue virus prophylactic or therapeutic compound. A single dengue vaccine, Sanofi Pasteur's Dengvaxia®, has been licensed in 20 countries but uptake has been poor. A safety signal in dengue seronegative vaccine recipients stimulated an international re-look at the vaccine performance profile, new World Health Organization recommendations for use, and controversy in the Philippines involving the government, regulatory agencies, Sanofi Pasteur, clinicians responsible for testing and administering the vaccine, and the parents of vaccinated children. In this review, we provide an overview of Dengvaxia's® development and discuss what has been learned about product performance since its licensure.

Cell-mediated immune responses to different formulations of a live-attenuated tetravalent dengue vaccine candidate in subjects living in dengue endemic and non-endemic regions

Three phase II randomized trials evaluated the safety/immunogenicity of two formulations of live-attenuated tetravalent dengue virus (TDEN) vaccine in dengue-endemic (Puerto Rico, Thailand) and non-endemic (US) regions (NCT00350337/NCT00370682/NCT00468858). We describe cell-mediated immune (CMI) responses; safety and humoral responses were reported previously. Participants received two doses of vaccine or control (placebo or the precursor live-attenuated TDEN vaccine) 6 months apart. Selected US participants received a booster 5–12 months post-dose 2. Evaluated subsets of the per-protocol cohorts included 75 primarily dengue virus (DENV)-unprimed US adults, 69 primarily flavivirus-primed Thai adults, and 100 DENV-primed or DENV-unprimed Puerto Rican adults/adolescents/children. T-cell responses were quantified using intracellular cytokine staining (ICS; DENV-infected cell-lysate or DENV-1/DENV-2 peptide-pool stimulation) or IFN-γ ELISPOT (DENV-2 peptide-pool stimulation). Memory B-cell responses were quantified using B-cell ELISPOT. Across populations and age strata, DENV serotype-specific CD4⁺ T-cell responses were slightly to moderately increased (medians ≤0.18% [ICS]), DENV-2–biased, and variable for both formulations. Responses in unprimed subjects were primarily detected post-dose 1. Response magnitudes in primed subjects were similar between doses. Multifunctional CD8⁺ T-cell responses were detected after peptide-pool stimulation. T-cell responses were mostly directed to DENV nonstructural proteins 3 and 5. Memory B-cell responses were tetravalent, of low-to-moderate magnitudes (medians ≤0.25%), and mainly observed post-dose 2 in unprimed subjects and post-dose 1 in primed subjects. A third dose did not boost CMI responses. In conclusion, both formulations of the live-attenuated TDEN vaccine candidate were poorly to moderately immunogenic with respect to B-cell and T-cell responses, irrespective of the priming status of the participants.

Abbreviation ATP: according-to-protocol; ICS: Intracellular Cytokine Staining; NS3: Nonstructural protein 3; ELISPOT: Enzyme-Linked ImmunoSpot; JEV: Japanese encephalitis virus; PBMC: peripheral blood mononuclear cells

Long-term immunogenicity and safety of tetravalent dengue vaccine (CYD-TDV) in healthy populations in Singapore and Vietnam: 4-year follow-up of randomized, controlled, phase II trials

Dengue is prevalent in the Asia-Pacific region. Participants of two immunogenicity and safety phase II studies conducted in Singapore and Vietnam (NCT0088089 and NCT00875524, respectively) were followed for up to four years after third vaccine dose of a recombinant, live, attenuated, tetravalent dengue vaccine (CYD-TDV). Participants (2–45 years) received three doses of CYD-TDV or control at 0, 6, and 12 months. Dengue plaque reduction neutralization test (PRNT₅₀) antibody titers were measured in both studies. Cytokine-producing antigen-specific CD4+ and CD8+ T-cells were quantified to assess cell-mediated immunity (CMI) in Singapore. Post-hoc analyses were carried out for participants aged <9 and ≥9 years old. Related and fatal serious adverse events (SAEs) were collected during long-term follow-up. Of participants who received ≥1 CYD-TDV injection in Singapore (n = 1198) and Vietnam (n = 180), 87% and 92% participants completed long-term follow-up, respectively. At four years, geometric mean titers (GMTs) in participants who received CYD-TDV ranged from 30.2 1/dil (95% CI 23.9–38.3) to 73.7 (49.3–110) 1/dil in Vietnam and 9.73 1/dil (95% CI 8.28–11.4) to 21.8 (18.9–25.1) 1/dil in Singapore. Interferon and interleukin-13 levels were lower at four years than one year post-vaccination but were still present. Tumor necrosis factor-α levels at four years were similar to those after the third vaccine dose. Seropositivity rates were higher at year four in participants who were seropositive vs. seronegative at baseline in both studies. No safety concerns were identified. CYD-TDV demonstrated long-term immunogenicity and was well-tolerated for four years after the third vaccine dose.

Refined efficacy estimates of the Sanofi Pasteur dengue vaccine CYD-TDV using machine learning

CYD-TDV is the first licensed dengue vaccine for individuals 9-45 (or 60) years of age. Using 12% of the subjects enroled in phase-2b and phase-3 trials for which baseline serostatus was measured, the vaccine-induced protection against virologically confirmed dengue during active surveillance (0-25 months) was found to vary with prior exposure to dengue. Because age and dengue exposure are highly correlated in endemic settings, refined insight into how efficacy varies by serostatus and age is essential to understand the increased risk of hospitalisation observed among vaccinated individuals during the long-term follow-up and to develop safe and effective vaccination strategies. Here we apply machine learning to impute the baseline serostatus for subjects with post-dose 3 titres but missing baseline serostatus. We find evidence for age dependence in efficacy independent of serostatus and estimate that among 9-16 year olds, CYD-TDV is protective against serotypes 1, 3 and 4 regardless of baseline serostatus.

Which Dengue Vaccine Approach Is the Most Promising, and Should We Be Concerned about Enhanced Disease after Vaccination? There Is Only One True Winner

The scientific community now possesses information obtained directly from human beings that makes it possible to understand why breakthrough-enhanced dengue virus (DENV) infections occurred in children receiving Sanofi Pasteur's Dengvaxia tetravalent live attenuated vaccine and to predict the possibility of breakthrough-enhanced DENV infections following immunization with two other tetravalent live attenuated vaccines now in phase III testing. Based upon recent research, Dengvaxia, lacking DENV nonstructural protein antigens, did not protect seronegatives because it failed to raise a competent T-cell response and/or antibodies to NS1. It is also possible that chimeric structure does not present the correct virion conformation permitting the development of protective neutralizing antibodies. A premonitory signal shared by the Sanofi Pasteur and the Takeda vaccines was the failure of fully immunized subhuman primates to prevent low-level viremia and/or anamnestic antibody responses to live DENV challenge. The vaccine developed by the National Institute of Allergy and Infectious Diseases (National Institutes of Health [NIH]) has met virtually all of the goals needed to demonstrate preclinical efficacy and safety for humans. Each monovalent vaccine was comprehensively studied for reactogenicity and immunogenicity in human volunteers. Protective immunity in subjects receiving tetravalent candidate vaccines was evidenced by the fact that when vaccinated subjects were given further doses of vaccine or different strains of DENV the result was "solid immunity," a nonviremic and nonanamnestic immune response.

Challenges in dengue research: A computational perspective

The dengue virus is now the most widespread arbovirus affecting human populations, causing significant economic and social impact in South America and South-East Asia. Increasing urbanization and globalization, coupled with insufficient resources for control, misguided policies or lack of political will, and expansion of its mosquito vectors are some of the reasons why interventions have so far failed to curb this major public health problem. Computational approaches have elucidated on dengue's population dynamics with the aim to provide not only a better understanding of the evolution and epidemiology of the virus but also robust intervention strategies. It is clear, however, that these have been insufficient to address key aspects of dengue's biology, many of which will play a crucial role for the success of future control programmes, including vaccination. Within a multiscale perspective on this biological system, with the aim of linking evolutionary, ecological and epidemiological thinking, as well as to expand on classic modelling assumptions, we here propose, discuss and exemplify a few major computational avenues-real-time computational analysis of genetic data, phylodynamic modelling frameworks, within-host model frameworks and GPU-accelerated computing. We argue that these emerging approaches should offer valuable research opportunities over the coming years, as previously applied and demonstrated in the context of other pathogens.

Phase I Randomized Study of a Tetravalent Dengue Purified Inactivated Vaccine in Healthy Adults from Puerto Rico

The safety and immunogenicity of four adjuvanted formulations of an investigational tetravalent dengue purified inactivated vaccine (DPIV) were evaluated in a predominantly dengue-primed population in Puerto Rico. In this placebo-controlled, randomized, observer-blind, phase I trial, 100 healthy adults were randomized 1:1:1:1:1 to receive DPIV at Day (D)0 and D28 (1 μg per dengue virus [DENV] type 1–4 adjuvanted with either alum, AS01_E or AS03_B, or 4 μg per DENV type adjuvanted with alum) or saline placebo. Functional antibody responses were assessed using a microneutralization assay at D56, Month (M)7, and M13. All DPIV formulations were well tolerated and no safety signals were identified through M13. The M13 according-to-protocol (ATP) immunogenicity cohort included 83 participants. The ATP analysis of immunogenicity was performed only on the 78 subjects seropositive for ≥ 1 DENV type at baseline: 69 tetravalent, three trivalent, two bivalent, and four monovalent. In all DPIV groups, geometric mean antibody titers (GMTs) increased from D0 to D56 and waned modestly through M13, while remaining well above prevaccination levels. The 4 μg + alum and the AS01_E- and AS03_B-adjuvanted formulations were highly immunogenic, with M13-neutralizing antibody GMTs against all four DENV types above 1,000. M13/D0 GMT ratios were highest in the 1 μg + AS03_B group (ranging 3.2–3.7 depending on the DENV type). These results encourage continued clinical development of DPIV (ClinicalTrials.gov: NCT01702857).

Neutralizing Antibody Correlates Analysis of Tetravalent Dengue Vaccine Efficacy Trials in Asia and Latin America

Background

In the CYD14 and CYD15 Phase 3 trials of the CYD-TDV dengue vaccine, estimated vaccine efficacy (VE) against symptomatic, virologically confirmed dengue (VCD) occurring between months 13 and 25 was 56.5% and 60.8%, respectively.

Methods

Neutralizing antibody titers to the 4 dengue serotypes in the CYD-TDV vaccine insert were measured at month 13 in a randomly sampled immunogenicity subcohort and in all VCD cases through month 25 (2848 vaccine, 1574 placebo) and studied for their association with VCD and with the level of VE to prevent VCD.

Results

For each trial and serotype, vaccinees with higher month 13 titer to the serotype had significantly lower risk of VCD with that serotype (hazard ratios, 0.19-0.43 per 10-fold increase). Moreover, for each trial, vaccinees with higher month 13 average titer to the 4 serotypes had significantly higher VE against VCD of any serotype (P < .001).

Conclusions

Neutralizing antibody titers postdose 3 correlate with CYD-TDV VE to prevent dengue. High titers associate with high VE for all serotypes, baseline serostatus groups, age groups, and both trials. However, lowest titers do not fully correspond to zero VE, indicating that other factors influence VE.

Dengue vaccines: implications for dengue control

PURPOSE OF REVIEW

Dengue, the most common arbovirus, is an increasingly significant cause of morbidity worldwide. After decades of research, an approved tetravalent dengue vaccine is finally available. Models constructed using recently available vaccine efficacy data allow for a data-driven discussion of the potential impact of dengue vaccine deployment on global control.

RECENT FINDINGS

Phase 3 efficacy trials demonstrated that the approved dengue vaccine, chimeric yellow fever-dengue-tetravalent dengue vaccine, has an efficacy of 60% against dengue illness of any severity. However, among dengue unexposed recipients, vaccination offers limited efficacy and may increase dengue severity. The WHO consequently recommends dengue vaccination for populations in which 70% of intended recipients are dengue seropositive. Models predict that routine childhood dengue vaccine may reduce dengue burden, but over time, population-level impact may be limited. Additional vaccine candidates in late-stage development may not suffer from the same limitations as chimeric yellow fever-dengue-tetravalent dengue vaccine.

SUMMARY

The efficacy and safety profile of the recently approved dengue vaccine is favorable only in previously dengue exposed recipients, which limits its potential for global control. Future work must evaluate the approved vaccine's long-term durability, efficacy of other late phase vaccine candidates, and potential for vector control efforts to work synergistically with vaccine deployment.

Integrated immunogenicity analysis of a tetravalent dengue vaccine up to 4 y after vaccination

Two large pivotal phase III studies demonstrated the efficacy of the tetravalent dengue vaccine (CYD-TDV; Dengvaxia®, Sanofi Pasteur) against all dengue serotypes. Here we present an unprecedented integrated summary of the immunogenicity of CYD-TDV to identify the parameters driving the neutralizing humoral immune response and evolution over time. We summarized the immunogenicity profiles of a 3-dose schedule of CYD-TDV administered 6 months apart across 10 phase II and 6 phase III trials undertaken in dengue endemic and non-endemic countries. Dengue neutralizing antibody titers in sera were determined at centralized laboratories using the 50% plaque reduction neutralization test (PRNT50) at baseline, 28 d after the third dose, and annually thereafter for up to 4 y after the third dose in some studies. CYD-TDV elicits neutralizing antibody responses against all 4 dengue serotypes; geometric mean titers (GMTs) increased from baseline to post-dose 3. GMTs were influenced by several parameters including age, baseline dengue seropositivity and region. In the 2 pivotal studies, GMTs decreased initially during the first 2 y post-dose 3 but appear to stabilize or slightly increase again in the third year. GMTs persisted 1.2-3.2-fold higher than baseline levels for up to 4 y post-dose 3 in other studies undertaken in dengue endemic countries. Our integrated analysis captures the fullness of the CYD-TDV immunogenicity profile across studies, age groups and regions; by presenting the available data in this way general trends and substantial outliers within each grouping can be easily identified. CYD-TDV elicits neutralizing antibody responses against all dengue serotypes, with differences by age and endemicity, which persist above baseline levels in endemic countries.

Phase 1 Randomized Study of a Tetravalent Dengue Purified Inactivated Vaccine in Healthy Adults in the United States

The safety and immunogenicity of four formulations of an investigational tetravalent dengue purified inactivated vaccine (DPIV), formulated at 1 or 4 μg with aluminum hydroxide (alum) or at 1 μg with an adjuvant system (AS01_E or AS03_B), were evaluated in a first-time-in-human, placebo-controlled, randomized, observer-blind, phase 1 trial in the continental United States. Two doses of vaccine or placebo were administered intramuscularly 4 weeks apart to 100 healthy adults 18–39 years of age, randomized 1:1:1:1:1 to receive one of four DPIV formulations or saline placebo. The response to a third dose was evaluated in a subset of nine participants remote from primary vaccination. Humoral immunogenicity was assessed using a 50% microneutralization assay. All DPIV formulations were well tolerated. No vaccine-related serious adverse events were observed through 12 months after the second vaccine dose. In all DPIV groups, geometric mean antibody titers peaked at Day 56, waned through 6 months after the second vaccine dose, and then stabilized. In the nine subjects where boosting was evaluated, a strong anamnestic response was observed. These results support continuation of the clinical development of this dengue vaccine candidate (clinicaltrials.gov: NCT01666652).

Dengue vaccine safety signal: Immune enhancement, waning immunity, or chance occurrence?

A new dengue vaccine was associated with increased risk of hospitalized virologically-confirmed disease during year 3 of follow-up among children age 2-5years. Among hypotheses to explain this finding, we could not distinguish definitively between antibody dependent enhancement, waning immunity, or chance occurrence. However, any theory must account for the following: (a) the signal occurred mainly because of decreased dengue among controls rather than increased dengue among vaccinees; (b) among 48 data points, a statistically significant increase in hospitalization among vaccinated children occurred for only one age group, during one year, and in one region; (c) cumulative risk was similar for vaccinated vs. control children age 2-5years at the end of year 5 and lower for vaccinated vs. control children among older age groups; (d) the protective effect of vaccine against hospitalization decreased from years 1-2 to years 3-5 of follow-up for all age groups and regions.

Effective Protection Induced by a Monovalent DNA Vaccine against Dengue Virus (DV) Serotype 1 and a Bivalent DNA Vaccine against DV1 and DV2 in Mice

Dengue virus (DV) is the causal pathogen of dengue fever, which is one of the most rapidly spread mosquito-borne disease worldwide and has become a severe public health problem. Currently, there is no specific treatment for dengue; thus, a vaccine would be an effective countermeasure to reduce the morbidity and mortality. Although, the chimeric Yellow fever dengue tetravalent vaccine has been approved in some countries, it is still necessary to develop safer, more effective, and less costly vaccines. In this study, a DNA vaccine candidate pVAX1-D1ME expressing the prME protein of DV1 was inoculated in BALB/c mice via intramuscular injection or electroporation, and the immunogenicity and protection were evaluated. Compared with traditional intramuscular injection, administration with 50 μg pVAX1-D1ME via electroporation with three immunizations induced persistent humoral and cellular immune responses and effectively protected mice against lethal DV1 challenge. In addition, immunization with a bivalent vaccine consisting of pVAX1-D1ME and pVAX1-D2ME via electroporation generated a balanced IgG response and neutralizing antibodies against DV1 and DV2 and could protect mice from lethal challenge with DV1 and DV2. This study sheds new light on developing a dengue tetravalent DNA vaccine.

Safety and immunogenicity of one versus two doses of Takeda's tetravalent dengue vaccine in children in Asia and Latin America: interim results from a phase 2, randomised, placebo-controlled study

BACKGROUND

Dengue is the most common mosquito-borne viral disease in human beings, and vector control has not halted its spread worldwide. A dengue vaccine for individuals aged 9 years and older has been licensed, but there remains urgent medical need for a vaccine that is safe and effective against all four dengue virus serotypes (DENV-1-4) in recipients of all ages. Here, we present the preplanned interim analyses at 6 months of a tetravalent dengue vaccine candidate (TDV), which is comprised of an attenuated DENV-2 virus strain (TDV-2) and three chimeric viruses containing the premembrane and envelope protein genes of DENV-1, DENV-3, and DENV-4 genetically engineered into the attenuated TDV-2 genome backbone (TDV-1, TDV-3, and TDV-4).

METHODS

An ongoing phase 2, randomised, double-blind, placebo-controlled trial of a TDV is being done at three sites in dengue-endemic countries (Dominican Republic, Panama, and the Philippines) to determine its safety and immunogenicity over 48 months in healthy participants aged 2-17 years who were randomly assigned (1:2:5:1) using an interactive web response system (stratified by age) to subcutaneous TDV injection (one 0·5 mL dose containing 2·5 × 10⁴ plaque-forming units [PFU] of TDV-1; 6·3 × 10³ PFU of TDV-2; 3·2 × 10⁴ PFU of TDV-3; and 4·0 × 10⁵ PFU of TDV-4) in different dose schedules (two-dose regimen at 0 and 3 months, one dose at 0 months, or one dose at 0 months and a booster at 12 months) or placebo. The primary endpoint of this 6 month interim analysis was geometric mean titres (GMTs) of neutralising antibodies against DENV-1-4 in the per-protocol immunogenicity subset at 1 month, 3 months, and 6 months after the first injection. Safety was assessed as a secondary outcome as percentage of participants with serious adverse events in all participants who were injected (safety set), and solicited and unsolicited adverse events (immunogenicity subset). This trial is registered with ClinicalTrials.gov, number NCT02302066.

FINDINGS

1800 participants were enrolled between Dec 5, 2014, and Feb 13, 2015. 1794 participants were given study injection as follows: 200 participants were given two-dose regimen at 0 and 3 months (group 1), 398 were given one dose at 0 months (group 2), 998 were given one dose at 0 months and will be given (trial ongoing) a booster at 12 months (group 3), and 198 were given placebo (group 4). These 1794 participants were included in the safety set; 562 participants were randomly assigned to the immunogenicity subset, of which 503 were included in the per-protocol set. TDV elicited neutralising antibodies against all DENV serotypes, which peaked at 1 month and remained elevated above baseline at 6 months. At 6 months, GMTs of neutralising antibodies against DENV-1 were 489 (95% CI 321-746) for group 1, 434 (306-615) for group 2, 532 (384-738) for group 3, and 62 (32-120) for group 4; GMTs of neutralising antibodies against DENV-2 were 1565 (1145-2140) for group 1, 1639 (1286-2088) for group 2, 1288 (1031-1610) for group 3, and 86 (44-169) for group 4; GMTs of neutralising antibodies against DENV-3 were 160 (104-248) for group 1, 151 (106-214) for group 2, 173 (124-240) for group 3, and 40 (23-71) for group 4; and GMTs of neutralising antibodies against DENV-4 were 117 (79-175) for group 1, 110 (80-149) for group 2, 93 (69-125) for group 3, and 24 (15-38) for group 4. No vaccine-related serious adverse events occurred; 15 (3%) of 562 participants in the immunogenicity subset reported vaccine-related unsolicited adverse events. The reactogenicity profile of TDV was acceptable, and similar to previous findings with TDV.

INTERPRETATION

TDV is safe and immunogenic in individuals aged 2-17 years, irrespective of previous dengue exposure. A second TDV dose induced enhanced immunogenicity against DENV-3 and DENV-4 in children who were seronegative before vaccination. These data supported the initiation of phase 3 evaluation of the efficacy and safety of TDV given in a two-dose schedule 3 months apart, with analyses that take into account baseline age and dengue serostatus.

FUNDING

Takeda Vaccines.

Licensed Dengue Vaccine: Public Health Conundrum and Scientific Challenge

A tetravalent live attenuated vaccine composed of chimeras of yellow fever 17D and the four dengue viruses (chimeric yellow fever dengue [CYD]) manufactured by Sanofi Pasteur has completed phase III clinical testing in over 35,000 children 2-16 years of age. The vaccine was recently licensed in four countries. During the first 2 years of observation, CYD vaccine efficacy ranged between 30% and 79% in 10 different countries with an overall efficacy of 56.8%. During year 3, there was an overall efficacy against hospitalization of 16.7%, but a relative risk of hospitalization of 1.6 among children younger than 9 years and 4.95 in children 5 years of age and younger. Vaccination of seronegative children resulted in universal broad dengue neutralizing antibody responses, but poor protection against breakthrough dengue cases. Unless proven otherwise, such breakthrough cases in vaccinated subjects should be regarded as vaccine antibody-enhanced (ADE). The provenance of these cases can be studied serologically using original antigenic sin immune responses in convalescent sera. In conventional dengue vaccine efficacy clinical trials, persons vaccinated as seronegatives may be hospitalized with breakthrough ADE infections, whereas in the placebo group, dengue infection of monotypic immunes results in hospitalization. Vaccine efficacy trial design must identify dengue disease etiology by separately measuring efficacy in seronegatives and seropositives. The reason(s) why CYD vaccine failed to raise protective dengue virus immunity are unknown. To achieve a safe and protective dengue vaccine, careful studies of monotypic CYD vaccines in humans should precede field trials of tetravalent formulations.

Benefits and risks of the Sanofi-Pasteur dengue vaccine: Modeling optimal deployment

The first approved dengue vaccine has now been licensed in six countries. We propose that this live attenuated vaccine acts like a silent natural infection in priming or boosting host immunity. A transmission dynamic model incorporating this hypothesis fits recent clinical trial data well and predicts that vaccine effectiveness depends strongly on the age group vaccinated and local transmission intensity. Vaccination in low-transmission settings may increase the incidence of more severe "secondary-like" infection and, thus, the numbers hospitalized for dengue. In moderate transmission settings, we predict positive impacts overall but increased risks of hospitalization with dengue disease for individuals who are vaccinated when seronegative. However, in high-transmission settings, vaccination benefits both the whole population and seronegative recipients. Our analysis can help inform policy-makers evaluating this and other candidate dengue vaccines.

Dengue serotype immune-interactions and their consequences for vaccine impact predictions

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The firstever dengue vaccine, Dengvaxia^®, has recently been licensed for use in several countries.

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Mathematical models are valuable tools for assessing vaccination impact on dengue burden.

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Model assumptions regarding dengue serotype immune interactions are inconsistent.

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Our results demonstrate how model assumptions critically affect vaccine impact predictions.

Dengue is one of the most important and wide-spread viral infections affecting human populations. The last few decades have seen a dramatic increase in the global burden of dengue, with the virus now being endemic or near-endemic in over 100 countries world-wide. A recombinant tetravalent vaccine candidate (CYD-TDV) has recently completed Phase III clinical efficacy trials in South East Asia and Latin America and has been licensed for use in several countries. The trial results showed moderate-to-high efficacies in protection against clinical symptoms and hospitalisation but with so far unknown effects on transmission and infections per se. Model-based predictions about the vaccine's short- or long-term impact on the burden of dengue are therefore subject to a considerable degree of uncertainty. Furthermore, different immune interactions between dengue's serotypes have frequently been evoked by modelling studies to underlie dengue's oscillatory dynamics in disease incidence and serotype prevalence. Here we show how model assumptions regarding immune interactions in the form of antibody-dependent enhancement, temporary cross-immunity and the number of infections required to develop full immunity can significantly affect the predicted outcome of a dengue vaccination campaign. Our results thus re-emphasise the important gap in our current knowledge concerning the effects of previous exposure on subsequent dengue infections and further suggest that intervention impact studies should be critically evaluated by their underlying assumptions about serotype immune-interactions.

Age specific differences in efficacy and safety for the CYD-tetravalent dengue vaccine

CYD-TDV is the first dengue vaccine to have completed Phase 3 efficacy trials. Efficacy was consistently higher in those aged 9 and above for all variables studied: efficacy against virologically confirmed dengue of any severity and serotype, serotype specific efficacy, efficacy dependent on baseline seropositivity, efficacy against hospitalizations and efficacy against severe disease. Because of the higher efficacy and the absence of a safety signal, the age group with the best benefit of the use of CYD-TDV is individuals aged 9 and above - the age group for which licensure is now being sought.

Protective and immunological behavior of chimeric yellow fever dengue vaccine

Clinical observations from the third year of the Sanofi Pasteur chimeric yellow fever dengue tetravalent vaccine (CYD) trials document both protection and vaccination-enhanced dengue disease among vaccine recipients. Children who were 5 years-old or younger when vaccinated experienced a DENV disease resulting in hospitalization at 5 times the rate of controls. On closer inspection, hospitalized cases among vaccinated seropositives, those at highest risk to hospitalized disease accompanying a dengue virus (DENV) infection, were greatly reduced by vaccination. But, seronegative individuals of all ages after being vaccinated were only modestly protected from mild to moderate disease throughout the entire observation period despite developing neutralizing antibodies at high rates. Applying a simple epidemiological model to the data, vaccinated seronegative individuals of all ages were at increased risk of developing hospitalized disease during a subsequent wild type DENV infection. The etiology of disease in placebo and vaccinated children resulting in hospitalization during a DENV infection, while clinically similar are of different origin. The implications of the observed mixture of DENV protection and enhanced disease in CYD vaccinees are discussed.

Immune correlates for dengue vaccine development

Dengue virus is the leading cause of vector-borne viral disease with four serotypes in circulation. Vaccine development has been complicated by the potential for both protection and disease enhancement during heterologous infection. Secondary infection triggers cross-reactive immune memory responses that have varying functional and epitope specificities that determine protection or risk. Strongly neutralizing antibodies to quaternary epitopes may be especially important for virus neutralization. Cell-mediated immunity dominated by Th1 functions may also play an important role. Determining an immune correlate of protection or risk would be highly beneficial for vaccine development but is hampered by mechanistic uncertainties and assay limitations. Clinical efficacy trials and human infection models along with a systems approach may provide future opportunities to elucidate such correlates.