Live-attenuated, tetravalent dengue vaccine in children, adolescents and adults in a dengue endemic country: Randomized controlled phase I trial in the Philippines

Dengue Fever Epidemics and the Prospect of Vaccines: A Systematic Review and Meta-Analysis Using Clinical Trials in Children

About half of the world's population is at risk of dengue infection. Epidemics of dengue fever have caused an increased risk of morbidity and mortality in recent years, which led to the exploration of vaccines as a preventive measure. This systematic review and meta-analysis aimed to evaluate the efficacy, immune response, and safety of dengue vaccines in children by analyzing clinical trials. The review followed standard procedures for data extraction using PRISMA guidelines and searching multiple databases, including PubMed, CINAHL, Medline, Health Source, Science Direct, and Academic Search Premiere. Eligible studies involved children (0-17 years old). Quality assessment was analyzed using the Cochrane Collaboration criteria, while data synthesis was conducted using thematic analysis and meta-analysis. Among the 38 selected studies, dengue vaccines showed varying efficacy against all four serotypes. The CYD-TDV (Dengvaxia®) and Tekade (TAK-003) vaccines showed strong protection against severe dengue, but their long-term efficacy varied. Vaccines triggered satisfactory immune responses, notably in those previously exposed to dengue. Safety profiles were mostly favorable, noting mild adverse events post-vaccination. Meta-analysis supported vaccine efficacy and immune response, but safety concerns warrant further exploration. In conclusion, dengue vaccines showed promising efficacy and immune response, particularly against severe manifestations.

Heterologous prime-boost immunization induces protection against dengue virus infection in cynomolgus macaques

IMPORTANCE

Currently licensed dengue vaccines do not induce long-term protection in children without previous exposure to dengue viruses in nature. These vaccines are based on selected attenuated strains of the four dengue serotypes and employed in combination for two or three consecutive doses. In our search for a better dengue vaccine candidate, live attenuated strains were followed by non-infectious virus-like particles or the plasmids that generate these particles upon injection into the body. This heterologous prime-boost immunization induced elevated levels of virus-specific antibodies and helped to prevent dengue virus infection in a high proportion of vaccinated macaques. In macaques that remained susceptible to dengue virus, distinct mechanisms were found to account for the immunization failures, providing a better understanding of vaccine actions. Additional studies in humans in the future may help to establish whether this combination approach represents a more effective means of preventing dengue by vaccination.

Nanomedicine as a potential novel therapeutic approach against the dengue virus

Dengue is an arbovirus infection which is transmitted by Aedes mosquitoes. Its prompt detection and effective treatment is a global health challenge. Various nanoparticle-based vaccines have been formulated to present immunogen (antigens) to instigate an immune response or prevent virus spread, but no specific treatment has been devised. This review explores the role of nanomedicine-based therapeutic agents against dengue virus, taking into consideration the applicable dengue virus assays that are sensitive, specific, have a short turnaround time and are inexpensive. Various kinds of metallic, polymeric and lipid nanoparticles with safe and effective profiles present an alternative strategy that could provide a better remedy for eradicating the dengue virus.

Biologics for dengue prevention: up-to-date

INTRODUCTION

Dengue is a worsening global public health problem. The vector-viral-host interactions driving the pathogenesis of dengue are multi-dimensional. Sequential dengue virus (DENV) infections with different DENV types significantly increase the risk of severe disease. Treatment is supportive in nature as there are no licensed anti-DENV antivirals or immuno-therapeutics. A single dengue vaccine has widely been licensed with two others in advanced clinical development. Dengvaxia® has been licensed in numerous countries but uptake has been slow as a result of safety signals noted in the youngest recipients and those who were dengue naïve at the time of vaccination.

AREAS COVERED

In this review, the current state of dengue vaccine and antiviral drug development will be discussed as well as new developments in controlled human infection models to support product development.

EXPERT OPINION

The world needs a safe and efficacious tetravalent dengue vaccine capable of protecting multiple different populations across a broad age range and different flavivirus immunologic backgrounds. Safe and effective antivirals are also needed to prevent or attenuate dengue disease in the unvaccinated, in cases of vaccine failure, or in high-risk populations.

A multiple-target mRNA-LNP vaccine induces protective immunity against experimental multi-serotype DENV in mice

Dengue virus (DENV) is a mosquito-borne virus with a rapid spread to humans, causing mild to potentially fatal illness in hundreds of millions of people each year. Due to the large number of serotypes of the virus, there remains an unmet need to develop protective vaccines for a broad spectrum of the virus. Here, we constructed a modified mRNA vaccine containing envelope domain III (E-DIII) and non-structural protein 1 (NS1) coated with lipid nanoparticles. This multi-target vaccine induced a robust antiviral immune response and increased neutralizing antibody titers that blocked all four types of DENV infection in vitro without significant antibody-dependent enhancement (ADE). In addition, there was more bias for Th1 than Th2 in the exact E-DIII and NS1-specific T cell responses after a single injection. Importantly, intramuscular immunization limited DENV transmission in vivo and eliminated vascular leakage. Our findings highlight that chimeric allogeneic structural and non-structural proteins can be effective targets for DENV vaccine and that they can prevent the further development of congenital DENV syndrome.

Plasmablast Expansion Following the Tetravalent, Live-Attenuated Dengue Vaccine Butantan-DV in DENV-Naïve and DENV-Exposed Individuals in a Brazilian Cohort

An effective vaccine against the dengue virus (DENV) should induce a balanced, long-lasting antibody (Ab) response against all four viral serotypes. The burst of plasmablasts in the peripheral blood after vaccination may reflect enriched vaccine-specific Ab secreting cells. Here we characterize the acute plasmablast responses from naïve and DENV-exposed individuals following immunization with the live attenuated tetravalent (LAT) Butantan DENV vaccine (Butantan-DV). The frequency of circulating plasmablasts was determined by flow cytometric analysis of fresh whole blood specimens collected from 40 participants enrolled in the Phase II Butantan-DV clinical trial (NCT01696422) before and after (days 6, 12, 15 and 22) vaccination. We observed a peak in the number of circulating plasmablast at day 15 after vaccination in both the DENV naïve and the DENV-exposed vaccinees. DENV-exposed vaccinees experienced a significantly higher plasmablast expansion. In the DENV-naïve vaccinees, plasmablasts persisted for approximately three weeks longer than among DENV-exposed volunteers. Our findings indicate that the Butantan-DV can induce plasmablast responses in both DENV-naïve and DENV-exposed individuals and demonstrate the influence of pre-existing DENV immunity on Butantan DV-induced B-cell responses.

Short communication: Feasibility of dengue vaccine to infect different human cell lines: An alternative potency test using HEK293T cells

Dengue is caused by an arbovirus that belongs to the Flaviviridae family and there are four distinct, but close related, circulating serotypes. Dengue disease is of great importance for global public health, with vaccination being its main prophylactic measure. However, there is a paucity of biological models for evaluating tetravalent dengue vaccines. The aim of this study was to evaluate the susceptibility of human cell lines HEK293T and THP-1 to a commercial dengue vaccine and test the feasibility of this approach in the development of a potency assay with human cell lines, as a methodological alternative to the golden standard potency assay with VERO cells. In this context, we used a batch of the commercial vaccine Dengvaxia® (CYD-TDV) for the infection tests. We evaluated the presence of the vaccine virus in THP-1 cells, differentiated into macrophages (dTHP-1), and in HEK293T by confocal microscopy, using 4G2 pan-flavivirus antibody. Vaccine infectivity and potency were determined by immunocolorimetric assay using monoclonal antibodies specific for each serotype. The results indicated that the human strain HEK293T was responsive to the tetravalent vaccine, as shown by the presence of virus particles in the cell cytoplasm in a pattern similar to the one observed with VERO cells. Moreover, it was possible to determine the infectivity and potency values of each vaccine virus serotype in the HEK293T, with serotype 4 prevailing over the others. Thus, the human cell line HEK293T provides a potential candidate to be used in assays to determine potency and identity of tetravalent dengue vaccines.

Comparison of Neutralizing Dengue Virus B Cell Epitopes and Protective T Cell Epitopes With Those in Three Main Dengue Virus Vaccines

The four serotypes of Dengue virus (DENV1-4) are arboviruses (arthropod-borne viruses) that belong to the Flavivirus genus, Flaviviridae family. They are the causative agents of an infectious disease called dengue, an important global public health problem with significant social-economic impact. Thus, the development of safe and effective dengue vaccines is a priority according to the World Health Organization. Only one anti-dengue vaccine has already been licensed in endemic countries and two formulations are under phase III clinical trials. In this study, we aimed to compare the main anti-dengue virus vaccines, DENGVAXIA®, LAV-TDV, and TAK-003, regarding their antigens and potential to protect. We studied the conservation of both, B and T cell epitopes involved in immunological control of DENV infection along with vaccine viruses and viral isolates. In addition, we assessed the population coverage of epitope sets contained in each vaccine formulation with regard to different human populations. As main results, we found that all three vaccines contain the main B cell epitopes involved in viral neutralization. Similarly, LAV-TDV and TAK-003 contain most of T cell epitopes involved in immunological protection, a finding not observed in DENGVAXIA®, which explains main limitations of the only licensed dengue vaccine. In summary, the levels of presence and absence of epitopes that are target for protective immune response in the three main anti-dengue virus vaccines are shown in this study. Our results suggest that investing in vaccines that contain the majority of epitopes involved in protective immunity (cellular and humoral arms) is an important issue to be considered.

Dengue Vaccines: The Promise and Pitfalls of Antibody-Mediated Protection

More than 390 million human dengue virus (DENV) infections occur each year, worldwide. Dengvaxia, a live-virus tetravalent vaccine from Sanofi Pasteur, was recently approved for human clinical use, although vaccine performance against the four DENV serotypes is highly variable. Other dengue vaccines in advanced clinical testing also demonstrate variability in efficacy. In this review, we outline the benefits and challenges of developing a safe, effective, and balanced DENV vaccine that can provide uniform protection against all four serotypes. Even though T cell biology plays an important role in establishing protective immunity, this review focuses on B cell responses. We discuss the leading dengue vaccine candidates and review the specificity of antibody responses and the known immune correlates of protection against DENV infection. A better understanding of immune correlates of protection against DENV infection will inform the development of a vaccine that can provide long-term, uniform protection.

Immunogenicity and safety of simplified vaccination schedules for the CYD-TDV dengue vaccine in healthy individuals aged 9-50 years (CYD65): a randomised, controlled, phase 2, non-inferiority study

BACKGROUND

Three doses of the licensed tetravalent dengue vaccine CYD-TDV (Dengvaxia, Sanofi Pasteur, Lyon France) are immunogenic and effective against symptomatic dengue in individuals aged 9 years and older who are dengue seropositive. Previous trials have provided some evidence that antibody responses elicited after just one dose or two doses of CYD-TDV might be similar to those elicited after three doses. We compared antibody responses following one-dose, two-dose, and three-dose vaccination regimens in individuals who were dengue seropositive at baseline up to 1 year after the last injection.

METHODS

In this randomised, controlled, phase 2, non-inferiority study (CYD65), healthy individuals aged 9-50 years were recruited from the community in three sites in Colombia and three sites in the Philippines. Participants were randomly assigned (1:1:1), using a permuted block method with stratification by site and age group, to receive, at 6-month intervals (on day 0, month 6, and month 12), three doses of CYD-TDV (three-dose group), one dose of placebo (on day 0) and two doses of CYD-TDV (at months 6 and 12; two-dose group), or two doses of placebo (on day 0 and month 6) and one dose of CYD-TDV (at month 12; one-dose group). Each dose of CYD-TDV was 0·5 mL, administered subcutaneously into the deltoid of the upper arm. Participants, study staff, investigators, and the funder were masked to group assignment. The co-primary endpoints were geometric mean titres (GMTs) of neutralising antibodies against each dengue virus serotype at 28 days and 1 year after the last vaccine injection. After a protocol amendment during the conduct of the study, the original co-primary objectives of non-inferiority of the one-dose and two-dose groups to the three-dose group were altered to include non-inferiority of the two-dose group to the three-dose group only, to be assessed in individuals who were dengue seropositive at baseline. Non-inferiority was shown if the lower limit of the 95% CI for the ratio of GMTs (GMR) at 28 days and 1 year between groups was more than 0·5 for each serotype. The analysis of the coprimary objectives was done in the per-protocol analysis dataset, which included all participants who had been vaccinated, had no protocol deviations, and had a valid serology test result for at least one dengue serotype at 28 days after the third injection. Safety was assessed throughout in all participants who received at least one injection of study drug, regardless of serostatus. This trial is registered with ClinicalTrials.gov, NCT02628444, and is closed to accrual.

FINDINGS

Between May 2, 2016, and Sept 16, 2016, we recruited and enrolled 1050 individuals, of whom 1048 received at least one injection and 993 had at least one blood sample taken (full-analysis dataset; 333 in three-dose group, 328 in two-dose group, and 332 in one-dose group). 860 (86·6%) of 993 participants in the full-analysis dataset were dengue seropositive at baseline. Non-inferiority (two dose vs three dose) was shown for each serotype at both 28 days and 1 year among dengue-seropositive participants (number of participants assessed: 272 [two-dose group], 265 [three-dose group] at 28 days; and 190 [two-dose group], 185 [three-dose group] at 1 year). At 28 days after the last injection, neutralising antibody GMTs were 899 (95% CI 752-1075) in the two-dose group versus 822 (700-964) in the three dose group against dengue serotype 1 (GMR 1·09 [95% CI 0·86-1·39]); 869 (754-1002) versus 875 (770-995) against serotype 2 (GMR 0·99 [0·82-1·20]); 599 (524-685) versus 610 (535-694) against serotype 3 (GMR 0·98 [0·82-1·18]); and 510 (453-575) versus 531 (470-601) against serotype 4 (GMR 0·96 [0·81-1·14]). At year 1, GMTs had decreased but remained above baseline for all serotypes: 504 (95% CI 403-630) in the two-dose group versus 490 (398-604) in the three-dose group against serotype 1 (GMR 1·03 [0·76-1·40]); 737 (611-888) versus 821 (704-957) against serotype 2 (GMR 0·90 [0·71-1·14]); 437 (368-519) versus 477 (405-561) against serotype 3 (GMR 0·92 [0·72-1·16]); and 238 (205-277) versus 270 (235-310) against serotype 4 (GMR 0·88 [0·72-1·09]). Reactogenicity profiles were similar across treatment groups. Most unsolicited adverse events after any injection were non-serious and systemic in nature. During the study, 60 serious adverse events were reported in 58 participants (14 in three-dose group, 26 in two-dose group, 18 in one-dose group), mostly infection and infestations or injury, poisoning, and procedural complications. No serious adverse events of special interest or admissions to hospital for dengue occurred. Two deaths occurred, unrelated to study treatment.

INTERPRETATION

A two-dose CYD-TDV regimen might be an alternative to the licensed three-dose regimen in individuals who are dengue seropositive at baseline and aged 9 years and older. Vaccination with a reduced number of doses could lead to improved vaccine compliance and coverage, especially in low-resource settings.

FUNDING

Sanofi Pasteur.

Combine dengue vaccines to optimize effectiveness

Developing a completely effective and safe dengue vaccine has been a complicated process. Dengvaxia®, by Sanofi-Pasteur, and recently TAK003, by Takeda, have strengths and weaknesses, but they seem to complement each other. In this work, we elaborate a rationale that could be applicable in a combined program of these vaccines for the control of dengue.

Anti-dengue Vaccines: From Development to Clinical Trials

Dengue Virus (DENV) is an arbovirus (arthropod-borne virus). Four serotypes of DENV are responsible for the infectious disease called dengue that annually affects nearly 400 million people worldwide. Although there is only one vaccine formulation licensed for use in humans, there are other vaccine formulations under development that apply different strategies. In this review, we present information about anti-dengue vaccine formulations regarding development, pre-clinical tests, and clinical trials. The improvement in vaccine development against dengue is much needed, but it should be considered that the correlate of protection is still uncertain. Neutralizing antibodies have been proposed as a correlate of protection, but this ignores the key role of T-cell mediated immunity in controlling DENV infection. It is important to confirm the accurate correlate of protection against DENV infection, and also to have other anti-dengue vaccine formulations licensed for use.

Adaptive Immunity to Dengue Virus: Slippery Slope or Solid Ground for Rational Vaccine Design?

The four serotypes of dengue virus are the most widespread causes of arboviral disease, currently placing half of the human population at risk of infection. Pre-existing immunity to one dengue virus serotype can predispose to severe disease following secondary infection with a different serotype. The phenomenon of immune enhancement has complicated vaccine development and likely explains the poor long-term safety profile of a recently licenced dengue vaccine. Therefore, alternative vaccine strategies should be considered. This review summarises studies dissecting the adaptive immune responses to dengue virus infection and (experimental) vaccination. In particular, we discuss the roles of (i) neutralising antibodies, (ii) antibodies to non-structural protein 1, and (iii) T cells in protection and pathogenesis. We also address how these findings could translate into next-generation vaccine approaches that mitigate the risk of enhanced dengue disease. Finally, we argue that the development of a safe and efficacious dengue vaccine is an attainable goal.

Dengue: Status of current and under-development vaccines

Dengue is an emerging mosquito-borne viral infection with increasing reports of outbreaks. The clinical picture ranges from a benign febrile illness through to severe and potentially fatal manifestations. No specific anti-viral treatment exists, and therapy only consists of supportive care. During the last three decades, several attempts to develop an effective vaccine have been made. The first dengue vaccine to obtain licensure was Dengvaxia, which was authorized in 2015 and is currently available in over 20 countries. Its use has been approved with strict limitations regarding age and serostatus of the recipients, highlighting the necessity for a more safe and efficacious vaccine. At present several vaccine, candidates are undergoing clinical and pre-clinical trials. The most advanced candidates are TDV and TDV 003/005, two live-attenuated vaccines, but another 15 vaccines are under development, introducing novel immunization strategies to the traditional dengue vaccine scenario. This work reviews the current research status on dengue vaccines.

Evaluation of rapid diagnostic tests and conventional enzyme-linked immunosorbent assays to determine prior dengue infection

BACKGROUND

In September 2018, the World Health Organization recommended that prevaccination screening be used with the tetravalent dengue vaccine (CYD-TDV), to ensure that only individuals with evidence of prior dengue infection (PDI) are vaccinated. Dengue rapid diagnostic tests (RDTs) would offer a potential solution for prevaccination screening at the point-of-care, but data on performance of available RDTs for identifying PDI are limited. We determined the suitability of four dengue RDTs and two conventional enzyme-linked immunosorbent assays (ELISAs) to identify PDI and evaluated cross-reactivity with co-circulating flaviviruses.

Methods: Specificity was assessed using 534 dengue-negative [determined by 50% plaque reduction neutralization test (PRNT50)] serum samples from USA (n = 229) and dengue-endemic regions (n = 305). Sensitivity was assessed using 270 samples from recent (n = 90) or remote (n = 90) virologically confirmed prior dengue cases, and dengue PRNT50-positive samples (n = 90). Cross-reactivity was assessed in dengue-seronegative samples that were seropositive for yellow fever (n = 57), Japanese encephalitis (n = 37), West Nile (n = 59) or Zika (n = 41).

Results: Dengue IgG RDTs and the Panbio ELISA exhibited favourable specificities (99-100%), higher than the Focus ELISA (95%). The RDTs had variable sensitivities (40-70%) that were lower than those of the ELISAs (≥90%). Cross-reactivity to other flaviviruses was low with RDTs (≤7%), but more significant with ELISAs (up to 51% for West Nile and 34% for Zika). No cross-reactivity to any of the four closely related flaviviruses was observed with the CTK Biotech RDT. For each SeroTest, sensitivity appeared similar in samples from individuals with recent (<13 months) vs remote (3-4 years) virologically confirmed PDI.

Conclusions: In general, dengue IgG RDTs were found to be more specific and less cross-reactive than the ELISAs, but the latter were more sensitive for identifying PDI cases. Currently available RDTs could be temporizing tools for rapid and safe prevaccination screening until improved RDTs with increased sensitivity become available.

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.

In vitro and in silico Models to Study Mosquito-Borne Flavivirus Neuropathogenesis, Prevention, and Treatment

Mosquito-borne flaviviruses can cause disease in the nervous system, resulting in a significant burden of morbidity and mortality. Disease models are necessary to understand neuropathogenesis and identify potential therapeutics and vaccines. Non-human primates have been used extensively but present major challenges. Advances have also been made toward the development of humanized mouse models, but these models still do not fully represent human pathophysiology. Recent developments in stem cell technology and cell culture techniques have allowed the development of more physiologically relevant human cell-based models. In silico modeling has also allowed researchers to identify and predict transmission patterns and discover potential vaccine and therapeutic candidates. This review summarizes the research on in vitro and in silico models used to study three mosquito-borne flaviviruses that cause neurological disease in humans: West Nile, Dengue, and Zika. We also propose a roadmap for 21st century research on mosquito-borne flavivirus neuropathogenesis, prevention, and treatment.

Dengue seroprevalence: data from the clinical development of a tetravalent dengue vaccine in 14 countries (2005-2014)

Dengue seroprevalence data in the literature is limited and the available information is difficult to compare between studies because of the varying survey designs and methods used. We assessed dengue seropositivity across 14 countries using data from 15 trials conducted during the development of a tetravalent dengue vaccine between October 2005 and February 2014. Participants’ dengue seropositivity (n=8592) was determined from baseline (before vaccination) serum samples at two centralized laboratories with the plaque reduction neutralization test (PRNT₅₀). Seropositivity rates generally increased with age in endemic settings. Although seropositivity rates varied across geographical areas, between countries, and within countries by region, no major differences were observed for given age groups between the two endemic regions, Latin America and Asia-Pacific. Seropositivity rates were generally stable over time. The proportion of participants who had only experienced primary infection tended to be higher in younger children than adolescents/adults. These results will help inform and guide dengue control strategies in the participating countries.

Trends in dengue research in the Philippines: A systematic review

Dengue is an important public health problem in the Philippines. We sought to describe the trends in dengue research in the country. We searched four databases and identified published studies on dengue research in the Philippines during the past 60 years. We reviewed 135 eligible studies, of which 33% were descriptive epidemiologic studies or case series, 16% were entomologic or vector control studies, 12% were studies on dengue virology and serologic response, 10% were socio-behavioral and economics studies, 8% were clinical trials, 7% were on burden of disease, 7% were investigations on markers of disease severity, 5% were on dengue diagnostics, and 2% were modeling studies. During the last decade, dengue research in the Philippines has increased and evolved from simple descriptive studies to those with more complex and diverse designs. We identified several key topics where more research would be useful.

Impact of Dengue Virus Serotype 2 Strain Diversity on Serological Immune Responses to Dengue

Dengue is a mosquito-borne disease caused by four dengue virus serotypes (DENV1-4) that are loosely categorized by sequence commonalities and antibody recognition profiles. The highly variable envelope protein (E) that is prominently displayed on the surface of DENV is an essential component of vaccines currently under development, yet the impact of using single strains to represent each serotype in tetravalent vaccines has not been adequately studied. We synthesized chimeric E by replacing highly variable residues from a dengue virus serotype 2 vaccine strain (PUO-218) with those from 16 DENV2 lineages spanning 60 years of antigen evolution. Examining sera from human and rhesus macaques challenged with single strains of DENV2, antibody-E interactions were markedly inhibited or enhanced by residues mainly focused within a 480 Ų footprint displayed on the E backbone. The striking impact of E diversity on polyclonal immune responses suggests that frequent antigen updates may be necessary for vaccines to counter shifts in circulating strains.

Dengue vaccination during pregnancy - An overview of clinical trials data

BACKGROUND

The live, attenuated, tetravalent dengue vaccine (CYD-TDV) is licensed in several endemic countries and contraindicated during pregnancy. Inadvertent vaccination during pregnancy may occur during clinical trials that include women of childbearing age. The potential risk associated with dengue vaccination in pregnancy remains unknown. We describe pregnancy outcomes following inadvertent dengue vaccination in pregnancy from CYD-TDV trial data.

METHODS

Data were collected from trials conducted as part of the CYD-TDV clinical development. Women who received CYD-TDV or placebo during the pre-specified pregnancy risk window (from 30 days before the date of their last menstrual period to end of pregnancy) were considered as exposed; pregnancies occurring in non-risk periods during the trials were considered to be non-exposed. Pregnancy losses were defined as abortion (spontaneous or unspecified), death in utero, and stillbirth.

RESULTS

615 pregnancies were reported from 19 CYD-TDV trials: 404 in the CYD-TDV arm, and 211 in the placebo arm. Exposure could not be determined for 7 pregnancies (5, CYD-TDV; 2, placebo). In the CYD-TDV arm, 58 pregnancies were considered as exposed. Most of these (n = 47, 81%) had healthy live births; 6 (10.3%) had pregnancy losses; 3 underwent elective termination and 2 had unknown outcome. In the placebo group, 30 pregnancies were considered exposed. Most of these (n = 25, 83%) had healthy births; 4 (13.3%) had pregnancy losses; and 1 had elective termination. Among non-exposed pregnancies, most resulted in healthy live births; 23/341 (6.7%) in the CYD-TDV group and 17/179 (9.5%) in the placebo group had pregnancy losses. Most reported pregnancy losses were in women considered high-risk for adverse pregnancy outcome, primarily due to young age.

CONCLUSION

In the small dataset assessed, no evidence of increased adverse pregnancy outcomes has been identified from inadvertent immunization of women in early pregnancy with CYD-TDV compared with the control group.

Seroprevalence of dengue among healthy adults in a rural community in Southern Malaysia: a pilot study

BACKGROUND

The frequency and magnitude of dengue epidemics continue to increase exponentially in Malaysia, with a shift in the age range predominance toward adults and an expansion to rural areas. Despite this, information pertaining to the extent of transmission of dengue virus (DENV) in the rural community is lacking. This community-based pilot study was conducted to establish DENV seroprevalence amongst healthy adults in a rural district in Southern Malaysia, and to identify influencing factors.

METHODS

In this study undertaken between April and May 2015, a total of 277 adult participants were recruited from households across three localities in the Sungai Segamat subdistrict in Segamat district. Sera were tested for immunoglobulin G (IgG) (Panbio® Dengue Indirect IgG ELISA/high-titer capture) and immunoglobulin M (IgM) (Panbio®) antibodies. The plaque reduction neutralization test (PRNT) was conducted on random samples of IgG-positive sera for further confirmation. Medical history and a recall of previous history of dengue were collected through interviews, whereas sociodemographic information was obtained from an existing database.

RESULTS

The overall seroprevalence for DENV infection was 86.6% (240/277) (95% CI: 83-91%). Serological evidence of recent infection (IgM/high-titer capture IgG) was noted in 11.2% (31/277) of participants, whereas there was evidence of past infection in 75.5% (209/277) of participants (indirect IgG minus recent infections). The PRNT assay showed that the detected antibodies were indeed specific to DENV. The multivariate analysis showed that the older age group was significantly associated with past DENV infections. Seropositivity increased with age; 48.5% in the age group of <25 years to more than 85% in age group of >45 years (P < 0.001). No associations with occupation, study site, housing type, comorbidity, educational level, and marital status were observed, although the latter two were statistically significant in the univariate analysis. None of the studied factors were significantly associated with recent DENV infections in the multivariate analysis, although there was a pattern suggestive of recent outbreak in two study sites populated predominately by Chinese people. The majority of infections did not give rise to recognizable disease (either asymptomatic or nonspecific symptoms) as only 12.9% of participants (31/240) recalled having dengue in the past.

CONCLUSIONS

The predominantly rural community under study had a very high previous exposure to dengue. The finding of a high proportion of unreported cases possibly due to subclinical infections underscores the need for enhanced surveillance and control methods. This finding also has implications for measuring disease burden, understanding transmission dynamics, and hypothesizing effects on DENV vaccine efficacy and uptake.

Replication and Excretion of the Live Attenuated Tetravalent Dengue Vaccine CYD-TDV in a Flavivirus-Naive Adult Population: Assessment of Vaccine Viremia and Virus Shedding

Background

We assessed replication and excretion of the live attenuated tetravalent dengue vaccine (CYD-TDV) into biological fluids following vaccination in dengue-naive adults in Australia.

Methods

Vaccinal viremia/shedding was assessed in a subset of participants enrolled in a lot-to-lot consistency study; 95 participants received 3 subcutaneous doses of CYD-TDV from phase 2/3 lots of the vaccine, and 8 received placebo; doses were administered 6 months apart. Quantitative reverse-transcription polymerase chain reaction (qR-PCR) analysis was used to initially detect the yellow fever virus (YFV) core protein gene in the backbone of CYD-TDV in serum, saliva and urine, followed by serotype-specific qRT-PCR analysis of samples positive for YFV by qRT-PCR (lower limit of detection, 5.16 GEq/mL).

Results

YFV viremia was detected by qRT-PCR in 69.5% of participants (66 of 95) who received CYD-TDV, mainly 6-14 days after injection 1. The serotypes detected were serotype 4 (in 68.2% of participants [45 of 95]), serotype 3 (in 19.7% [13 of 95]), and serotype 1 (in 12.1% [8 of 95]); serotype 2 was not detected. None of the placebo recipients had vaccinal viremia/shedding. No participants had detectable viral shedding into saliva at levels above the lower limit of quantitation. Two participants had low-level viral shedding (serotype 3) in urine (5.47 and 5.77 GEq/mL). None of the participants with viremia or shedding experienced concomitant fever.

Conclusions

Low-level vaccinal viremia may occur following vaccination with CYD-TDV, but this is not associated with any symptom or adverse event.

Clinical Trials Registration

NCT01134263.

Immune correlates of protection for dengue: State of the art and research agenda

Dengue viruses (DENV1-4) are mosquito-borne flaviviruses estimated to cause up to ∼400 million infections and ∼100 million dengue cases each year. Factors that contribute to protection from and risk of dengue and severe dengue disease have been studied extensively but are still not fully understood. Results from Phase 3 vaccine efficacy trials have recently become available for one vaccine candidate, now licensed for use in several countries, and more Phase 2 and 3 studies of additional vaccine candidates are ongoing, making these issues all the more urgent and timely. At the "Summit on Dengue Immune Correlates of Protection", held in Annecy, France, on March 8-9, 2016, dengue experts from diverse fields came together to discuss the current understanding of the immune response to and protection from DENV infection and disease, identify key unanswered questions, discuss data on immune correlates and plans for comparison of results across assays/consortia, and propose a research agenda for investigation of dengue immune correlates, all in the context of both natural infection studies and vaccine trials.

Clinical Efficacy, Safety, and Immunogenicity of a Live Attenuated Tetravalent Dengue Vaccine (CYD-TDV) in Children: A Systematic Review with Meta-analysis

BACKGROUND

Dengue hemorrhagic fever is the leading cause of hospitalization and death in children living in Asia and Latin America. There is an urgent need for an effective and safe dengue vaccine to reduce morbidity and mortality in this high-risk population given the lack of dengue specific treatment at present. This review aims to determine the efficacy, safety, and immunogenicity of CYD-TDV vaccine in children.

METHODS

This is a systematic review including meta-analysis of randomized controlled clinical trial data from Embase, Medline, the Cochrane Library, Web of Science, and ClinicalTrials.gov. Studies that assessed CYD-TDV vaccine efficacy [(1 - RR)*100], safety (RR), and immunogenicity (weighted mean difference) in children were included in this study. Random effects model was employed to analyze patient-level data extracted from primary studies.

RESULTS

The overall efficacy of CYD-TDV vaccine was 54% (40-64), while serotype-specific efficacy was 77% (66-85) for DENV4, 75% (65-82) for DENV3, 50% (36-61) for DENV1, and 34% (14-49) for DENV2. 15% (-174-74) vaccine efficacy was obtained for the unknown serotype. Meta-analysis of included studies with longer follow-up time (25 months) revealed that CYD-TDV vaccine significantly increased the risk of injection site reactions (RR = 1.1: 1.04-1.17; p-value = 0.001). Immunogenicity (expressed as geometric mean titers) in descending order was 439.7 (331.7-547.7), 323 (247 - 398.7), 144.1 (117.9-170.2), and 105 (88.7-122.8) for DENV3, DENV2, DENV1, and DENV4, respectively.

CONCLUSION

CYD-TDV vaccine is effective and immunogenic in children overall. Reduced efficacy of CYD-TDV vaccine against DENV2 notoriously known for causing severe dengue infection and dengue outbreaks cause for serious concern. Post hoc meta-analysis of long-term follow-up data (≥25 months) from children previously vaccinated with CYD-TDV vaccine is needed to make a conclusion regarding CYD-TDV vaccine safety in children. However, CYD-TDV vaccine should be considered for use in regions where DENV2 is not endemic as currently there is no specific treatment for dengue infection.

Immunogenicity and safety of a tetravalent dengue vaccine in healthy adults in India: A randomized, observer-blind, placebo-controlled phase II trial

Dengue is a mosquito-borne viral disease that is endemic in India. We evaluated the immunogenicity and safety of recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) in Indian adults. In this observer-blind, randomized, placebo-controlled, Phase II study, adults aged 18–45 years were randomized 2:1 to receive CYD-TDV or placebo at 0, 6 and 12 months in sub-cutaneous administration. Immunogenicity was assessed using a 50% plaque reduction neutralization test (PRNT₅₀) at baseline and 28 days after each study injection. 189 participants were enrolled (CYD-TDV [n = 128]; placebo, [n = 61]). At baseline, seropositivity rates for dengue serotypes 1, 2, 3 and 4 ranged from 77.0% to 86.9%. Seropositivity rates for each serotype increased after each CYD-TDV injection with a more pronounced increase after the first injection. In the CYD-TDV group, geometric mean titres (GMTs) were 2.38 to 6.11-fold higher after the third injection compared with baseline but remained similar to baseline in the placebo group. In the CYD-TDV group, the GMTs were 1.66 to 4.95-fold higher and 9.23 to 24.6-fold higher after the third injection compared with baseline in those who were dengue seropositive and dengue seronegative, respectively. Pain was the most commonly reported solicited injection site reaction after the first injection in both the CYD-TDV (6.3%) and placebo groups (4.9%), but occurred less frequently after subsequent injections. No serious adverse events were vaccine-related, no immediate unsolicited adverse events, and no virologically-confirmed cases of dengue, were reported during the study. The immunogenicity and safety of CYD-TDV was satisfactory in both dengue seropositive and seronegative Indian adults.

Immunogenicity and Safety of Yellow Fever Vaccine (Stamaril) When Administered Concomitantly With a Tetravalent Dengue Vaccine Candidate in Healthy Toddlers at 12-13 Months of Age in Colombia and Peru: A Randomized Trial

BACKGROUND

Dengue and yellow fever (YF) viruses are closely related members of the Flaviviridae family. Given the inherent similarities between the YF vaccine and dengue vaccine (CYD-TDV) candidate, it is possible that the latter could interfere with the response to the licensed YF vaccine when coadministered.

METHODS

In this randomized, observer-blind, controlled, phase III trial, conducted in Colombia and Peru, 787 toddlers were administered YF vaccine concomitantly with CYD-TDV (group 1) or placebo (group 2), followed by CYD-TDV after 6 and 12 months. YF and dengue neutralizing antibody titers were determined using a 50% plaque reduction neutralization test. Noninferiority was demonstrated if the lower limit of the 2-sided 95% confidence interval of the difference in seroconversion rates [(YF + CYD-TDV) - YF alone] was greater than -10%. The safety of both vaccines was also assessed.

RESULTS

Concomitant administration of YF with either CYD-TDV or placebo yielded YF seroconversion rates of 100.0% and 99.7%, respectively. The difference in YF seroconversion rates between the 2 groups was 0.33% (95% confidence interval:0.98; 1.87), demonstrating that the immune response against YF administered concomitantly with CYD-TDV was noninferior to YF administered with placebo. After 2 injections of CYD-TDV, the percentage of participants with dengue titres ≥10 (1/dil) for the 4 dengue serotypes were 91.2%-100% for group 1 and 97.2%-100% in group 2. There were no safety concerns during the study period.

CONCLUSIONS

Concomitant administration of YF vaccine with CYD-TDV has no relevant impact on the immunogenicity or safety profile of the YF vaccine.

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.

Neutropenia as an Adverse Event following Vaccination: Results from Randomized Clinical Trials in Healthy Adults and Systematic Review

BACKGROUND

In the context of early vaccine trials aimed at evaluating the safety profile of novel vaccines, abnormal haematological values, such as neutropenia, are often reported. It is therefore important to evaluate how these trials should be planned not to miss potentially important safety signals, but also to understand the implications and the clinical relevance.

METHODOLOGY

We report and discuss the results from five clinical trials (two with a new Shigella vaccine in the early stage of clinical development and three with licensed vaccines) where the absolute neutrophil counts (ANC) were evaluated before and after vaccination. Additionally, we have performed a systematic review of the literature on cases of neutropenia reported during vaccine trials to discuss our results in a more general context.

PRINCIPAL FINDINGS

Both in our clinical trials and in the literature review, several cases of neutropenia have been reported, in the first two weeks after vaccination. However, neutropenia was generally transient and had a benign clinical outcome, after vaccination with either multiple novel candidates or well-known licensed vaccines. Additionally, the vaccine recipients with neutropenia frequently had lower baseline ANC than non-neutropenic vaccinees. In many instances neutropenia occurred in subjects of African descent, known to have lower ANC compared to western populations.

CONCLUSIONS

It is important to include ANC and other haematological tests in early vaccine trials to identify potential safety signals. Post-vaccination neutropenia is not uncommon, generally transient and clinically benign, but many vaccine trials do not have a sampling schedule that allows its detection. Given ethnic variability in the level of circulating neutrophils, normal ranges taking into account ethnicity should be used for determination of trial inclusion/exclusion criteria and classification of neutropenia related adverse events.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02017899, NCT02034500, NCT01771367, NCT01765413, NCT02523287.

Dengue Fever: Causes, Complications, and Vaccine Strategies

Dengue is a highly endemic infectious disease of the tropical countries and is rapidly becoming a global burden. It is caused by any of the 4 serotypes of dengue virus and is transmitted within humans through female Aedes mosquitoes. Dengue disease varies from mild fever to severe conditions of dengue hemorrhagic fever and shock syndrome. Globalization, increased air travel, and unplanned urbanization have led to increase in the rate of infection and helped dengue to expand its geographic and demographic distribution. Dengue vaccine development has been a challenging task due to the existence of four antigenically distinct dengue virus serotypes, each capable of eliciting cross-reactive and disease-enhancing antibody response against the remaining three serotypes. Recently, Sanofi Pasteur's chimeric live-attenuated dengue vaccine candidate has been approved in Mexico, Brazil, and Philippines for usage in adults between 9 and 45 years of age. The impact of its limited application to the public health system needs to be evaluated. Simultaneously, the restricted application of this vaccine candidate warrants continued efforts in developing a dengue vaccine candidate which is additionally efficacious for infants and naïve individuals. In this context, alternative strategies of developing a designed vaccine candidate which does not allow production of enhancing antibodies should be explored, as it may expand the umbrella of efficacy to include infants and naïve individuals.

Safety Overview of a Recombinant Live-Attenuated Tetravalent Dengue Vaccine: Pooled Analysis of Data from 18 Clinical Trials

A recombinant live attenuated tetravalent dengue vaccine (CYD-TDV) has been shown to be efficacious in preventing virologically-confirmed dengue disease, severe dengue disease and dengue hospitalization in children aged 2-16 years in Asia and Latin America. We analyzed pooled safety data from 18 phase I, II and III clinical trials in which the dengue vaccine was administered to participants aged 2-60 years, including long-term safety follow-up in three efficacy trials. The participants were analyzed according to their age at enrollment. The percentage of participants aged 2-60 years reporting ≥1 solicited injection-site or systemic reactions was slightly higher in the CYD-TDV group than in the placebo group. The most common solicited injection-site reactions were pain. Headache and malaise were the most common solicited systemic reactions. In both groups 0.3% of participants discontinued for safety reasons. The most common unsolicited adverse events were injection-site reactions, gastrointestinal disorders, and infections. Reactogenicity did not increase with successive doses of CYD-TDV. The frequency and nature of SAEs occurring within 28 days of any dose were similar in the CYD-TDV and placebo groups and were common medical conditions that could be expected as a function of age. Baseline dengue virus serostatus did not appear to influence the safety profile. No vaccine-related anaphylactic reactions, neurotropic events or viscerotropic events were reported. In year 3 after dose 1, an imbalance for dengue hospitalization, including for severe dengue, observed in participants aged <9 years in the CYD-TDV group compared with the placebo group was not observed for participants aged ≥9 years. In Year 4, this imbalance in participants aged <9 years was less marked, giving an overall lower risk of dengue hospitalization or severe dengue from dose 1 to Year 4 in the CYD-TDV group. These results have contributed to the definition of the target population for vaccination (≥9 years old) for which CYD-TDV has a satisfactory safety profile. Long-term safety will continue to be monitored in the ongoing follow-up of efficacy trials. Safety and effectiveness in real-life settings will be assessed through post-licensure studies.

The tolerability of a combined hepatitis A and typhoid vaccine in children aged 2-16 years: an observational study

BACKGROUND

Combined hepatitis A and typhoid vaccines have been widely used globally and proven to be safe, well tolerated and efficacious in adults. The combined hepatitis A and typhoid vaccine (Vivaxim) available in Australia is licenced for use from age 16 years but the monovalent components are approved for use from age 2 years. Advantages of a single injection have led to widespread 'off-label' use of Vivaxim in children. This study aimed to investigate the tolerability of Vivaxim in children aged 2-16 years.

METHODS

A prospective observational study was conducted at Travel Medicine Alliance clinics across Australia. Children who required vaccination for both hepatitis A and typhoid were offered the option of receiving Vivaxim. Parents were contacted 3 days post-vaccination and asked to respond to a questionnaire on adverse events following immunization (AEFIs). Reactions to Vivaxim were compared with reported reactions to the monovalent vaccines.

RESULTS

Our study included 425 children who received Vivaxim, including 189 (44.5%) who received other vaccines on the same day. No serious AEFIs were reported, and 26.8% did not experience any side effects. In children who did not receive other vaccines in the same arm as Vivaxim (n = 325), most common local reactions were sore arm (70.5%), redness (16.0%) and swelling (11.1%). Reports of local AEFIs in our subjects was significantly more common than those reported for the individual monovalent vaccines. In children who did not receive other vaccines on the same day (n = 236), the most common systemic reactions were tiredness/lethargy/malaise (5.9%), headache (4.2%), fever (3.4%) and sore muscles and joints (3.4%). Fever was more common in children aged <6 years. Less than 5% of children reported missing school, sport or other regular activities.

CONCLUSIONS

Vivaxim was well tolerated in children aged 2-16 years. Parents should be advised about AEFIs to Vivaxim so that they can make informed decisions about vaccination options.

Epidemiology of Infant Dengue Cases Illuminates Serotype-Specificity in the Interaction between Immunity and Disease, and Changes in Transmission Dynamics

Background

Infants born to dengue immune mothers acquire maternal antibodies to dengue. These antibodies, though initially protective, decline during the first year of life to levels thought to be disease enhancing, before reaching undetectable levels. Infants have long been studied to understand the interaction between infection and disease on an individual level.

Methods/Findings

Considering infants (cases <1 year old) as a unique group, we analyzed serotype specific dengue case data from patients admitted to a pediatric hospital in Bangkok, Thailand. We show differences in the propensity of serotypes to cause disease in individuals with dengue antibodies (infants and post-primary cases) and in individuals without dengue antibodies (primary cases). The mean age of infant cases differed among serotypes, consistent with previously observed differential waning of maternal antibody titers by serotype. We show that trends over time in epidemiology of infant cases are consistent with those observed in the whole population, and therefore with trends in the force of infection.

Conclusions/Significance

Infants with dengue are informative about the interaction between antibody and the dengue serotypes, confirming that in this population DENV-2 and DENV-4 almost exclusively cause disease in the presence of dengue antibody despite infections occurring in others. We also observe differences between the serotypes in the mean age in infant cases, informative about the interaction between waning immunity and disease for the different serotypes in infants. In addition, we show that the mean age of infant cases over time is informative about transmission in the whole population. Therefore, ongoing surveillance for dengue in infants could provide useful insights into dengue epidemiology, particularly after the introduction of a dengue vaccine targeting adults and older children.

Infants born to dengue immune mothers acquire maternal dengue antibodies. These antibodies, though initially protective, decline during the first year of life to levels thought to be disease enhancing, before reaching undetectable levels. We show that in this population, DENV-2 and DENV-4 almost exclusively cause disease in the presence of dengue antibody, despite infections occurring in others. We also observe serotype-specificity in the mean age of infant cases, consistent with differential waning of antibody to each serotype. These results highlight serotype-specificity in the way the immune response interacts with infection to cause disease. In addition, we show that the mean age of infant cases over time is informative about transmission in the whole population. Therefore, ongoing surveillance for dengue in infants could provide useful insights into dengue epidemiology, particularly after the introduction of a dengue vaccine targeting adults and older children.

Tackling dengue fever: Current status and challenges

According to recent statistics, 96 million apparent dengue infections were estimated worldwide in 2010. This figure is by far greater than the WHO prediction which indicates the rapid spread of this disease posing a growing threat to the economy and a major challenge to clinicians and health care services across the globe particularly in the affected areas.This article aims at bringing to light the current epidemiological and clinical status of the dengue fever. The relationship between genetic mutations, single nucleotide polymorphism (SNP) and the pathophysiology of disease progression will be put into perspective. It will also highlight the recent advances in dengue vaccine development.Thus far, a significant progress has been made in unraveling the risk factors and understanding the molecular pathogenesis associated with the disease. However, further insights in molecular features of the disease and the development of animal models will enormously help improving the therapeutic interventions and potentially contribute to finding new preventive measures for population at risk.

Dengue vaccine: hypotheses to understand CYD-TDV-induced protection

Dengue virus (DENV) is a human pathogen with a large impact on public health. Although no vaccine against DENV is currently licensed, a recombinant vaccine - chimeric yellow fever virus-DENV tetravalent dengue vaccine (CYD-TDV) - has shown efficacy against symptomatic dengue disease in two recent Phase III clinical trials. Safety observations were also recently reported for these trials. In this Opinion article, we review the data from recent vaccine clinical trials and discuss the putative mechanisms behind the observed efficacy of the vaccine against different forms of the disease, focusing on the interactions between the infecting virus, pre-existing host immunity and vaccine-induced immune responses.

Estimation of parameters related to vaccine efficacy and dengue transmission from two large phase III studies

BACKGROUND

A tetravalent dengue vaccine was shown to be efficacious against symptomatic dengue in two phase III efficacy studies performed in five Asian and five Latin American countries. The objective here was to estimate key parameters of a dengue transmission model using the data collected during these studies.

METHODS

Parameter estimation was based on a Sequential Monte Carlo approach and used a cohort version of the transmission model. Serotype-specific basic reproduction numbers were derived for each country. Parameters related to serotype interactions included duration of cross-protection and level of cross-enhancement characterized by differences in symptomaticity for primary, secondary and post-secondary infections. We tested several vaccine efficacy profiles and simulated the evolution of vaccine efficacy over time for the scenarios providing the best fit to the data.

RESULTS

Two reference scenarios were identified. The first included temporary cross-protection and the second combined cross-protection and cross-enhancement upon wild-type infection and following vaccination. Both scenarios were associated with differences in efficacy by serotype, higher efficacy for pre-exposed subjects and against severe dengue, increase in efficacy with doses for naïve subjects and by a more important waning of vaccine protection for subjects when naïve than when pre-exposed. Over 20 years, the median reduction of dengue risk induced by the direct protection conferred by the vaccine ranged from 24% to 47% according to country for the first scenario and from 34% to 54% for the second.

CONCLUSION

Our study is an important first step in deriving a general framework that combines disease dynamics and mechanisms of vaccine protection that could be used to assess the impact of vaccination at a population level.

Laboratory-confirmed Dengue in Children in Three Regional Hospitals in the Philippines in 2009-2010

BACKGROUND

The burden of dengue is high in the Philippines but the prevalence of confirmed cases is unknown, and the disease is subject to underreporting because surveillance of suspected cases is passive. We conducted a prospective epidemiological study to estimate the proportion of laboratory-confirmed dengue among clinically suspected hospitalized cases in the pediatric wards of 3 regional hospitals in the Philippines and to describe the clinical and laboratory features, age distributions, case fatality rates and serotype distributions of these hospitalized cases.

METHODS

Patients ≤18 years and hospitalized for suspected dengue were included if they had an axillary temperature ≥38°C for 2-7 days and 2 or more dengue-associated symptoms. Dengue infection was confirmed in acute blood samples by serotype-specific reverse transcription-polymerase chain reaction and IgM immunoassay.

RESULTS

We confirmed dengue infection in 1809 (86.1%) cases of 2103 suspected cases between November 2009 and November 2010. The 6- to 10-year-old age group had the highest proportion of cases overall (36.7%). Fever, anorexia, myalgia, abdominal pain and headache were the most common symptoms at admission. Hemorrhagic manifestations, signs of plasma leakage, thrombocytopenia and leucopenia were all significantly more common in confirmed than in nonconfirmed cases. Most cases (76.5%) developed dengue hemorrhagic fever or dengue shock syndrome, and the overall case fatality rate was 0.94%. Distributions of all 4 virus serotypes varied at each hospital.

CONCLUSIONS

The clinical burden of pediatric dengue continues to be substantial in the Philippines. Most hospitalized cases of suspected pediatric dengue can be laboratory confirmed and most develop severe disease.

Guiding dengue vaccine development using knowledge gained from the success of the yellow fever vaccine

Flaviviruses comprise approximately 70 closely related RNA viruses. These include several mosquito-borne pathogens, such as yellow fever virus (YFV), dengue virus (DENV), and Japanese encephalitis virus (JEV), which can cause significant human diseases and thus are of great medical importance. Vaccines against both YFV and JEV have been used successfully in humans for decades; however, the development of a DENV vaccine has encountered considerable obstacles. Here, we review the protective immune responses elicited by the vaccine against YFV to provide some insights into the development of a protective DENV vaccine.

Safety and Immunogenicity of a Live Attenuated Tetravalent Dengue Vaccine Candidate in Flavivirus-Naive Adults: A Randomized, Double-Blinded Phase 1 Clinical Trial

BACKGROUND

Dengue viruses (DENVs) infect >300 million people annually, causing 96 million cases of dengue disease and 22 000 deaths [1]. A safe vaccine that protects against DENV disease is a global health priority [2].

METHODS

We enrolled 72 flavivirus-naive healthy adults in a phase 1 double-blinded, randomized, placebo-controlled dose-escalation trial (low and high dose) of a live attenuated recombinant tetravalent dengue vaccine candidate (TDV) given in 2 doses 90 days apart. Volunteers were followed for safety, vaccine component viremia, and development of neutralizing antibodies to the 4 DENV serotypes.

RESULTS

The majority of adverse events were mild, with no vaccine-related serious adverse events. Vaccinees reported injection site pain (52% vs 17%) and erythema (73% vs 25%) more frequently than placebo recipients. Low levels of TDV-serotype 2 (TDV-2), TDV-3, and TDV-4 viremia were observed after the first but not second administration of vaccine. Overall seroconversion rates and geometric mean neutralization titers after 2 doses were 84.2% and 54.1, respectively, for DENV serotype 1 (DENV-1); 92.1% and 292.8, respectively, for DENV-2; 86.8% and 32.3, respectively, for DENV-3; and 71.1% and 15.0, respectively, for DENV-4. More than 90.0% of high-dose recipients had trivalent or broader responses.

CONCLUSIONS

TDV was generally well tolerated, induced trivalent or broader neutralizing antibodies to DENV in most flavivirus-naive vaccinees, and is undergoing further development.

CLINICAL TRIALS REGISTRATION

NCT01110551.

Assessment of bivalent and tetravalent dengue vaccine formulations in flavivirus-naïve adults in Mexico

Several ChimeriVax-Dengue (CYD)-based vaccination strategies were investigated as potential alternatives to vaccination with tetravalent CYD vaccine (CYD-TDV) in this phase IIa trial conducted in 2008–9 in 150 healthy adults. Participants were randomized and vaccinated on D0 and D105 (± 15 days). One group received bivalent CYD vaccine against serotypes 1 and 3 (CYD-1;3) on day 0 and CYD-2;4 on day 105 (±15 days). Two groups received an injection at each timepoint of a tetravalent blend of CYD-1;3;4 and a VERO cell derived, live attenuated vaccine against serotype 2 (VDV-2), or the reference CYD-TDV. A fourth group received Japanese encephalitis (JE) vaccine on days -14, -7 and 0, followed by CYD-TDV on day 105. Viraemia was infrequent in all groups. CYD-4 viraemia was most frequent after tetravalent vaccination, while CYD-3 viraemia was most frequent after the first bivalent vaccination. Immunogenicity as assessed by 50% plaque reduction neutralisation test on D28 was comparable after the first injection of either tetravalent vaccine, and increased after the second injection, particularly with the blended CYD-1;3;4/ VDV-2 vaccine. In the bivalent vaccine group, immune response against serotype 3 was highest and the second injection elicited a low immune response against CYD 2 and 4. Immune responses after the first injection of CYD-TDV in the JE-primed group were in general higher than after the first injection in the other groups. All tested regimens were well tolerated without marked differences between groups. Bivalent vaccination showed no advantage in terms of immunogenicity.

Clinical trial registration number: NCT00740155

Lot-to-lot consistency of a tetravalent dengue vaccine in healthy adults in Australia: a randomised study

BACKGROUND

The recombinant yellow fever-17D-dengue virus, live, attenuated, tetravalent dengue vaccine (CYD-TDV) has undergone extensive clinical trials. Here safety and consistency of immunogenicity of phase III manufacturing lots of CYD-TDV were evaluated and compared with a phase II lot and placebo in a dengue-naïve population.

METHODS

Healthy 18-60 year-olds were randomly assigned in a 3:3:3:3:1 ratio to receive three subcutaneous doses of either CYD-TDV from any one of three phase III lots or a phase II lot, or placebo, respectively in a 0, 6, 12 month dosing schedule. Neutralising antibody geometric mean titres (PRNT50 GMTs) for each of the four dengue serotypes were compared in sera collected 28 days after the third vaccination-equivalence among lots was demonstrated if the lower and upper limits of the two-sided 95% CIs of the GMT ratio were ≥0.5 and ≤2.0, respectively.

RESULTS

712 participants received vaccine or placebo and 614 (86%) completed the study; 17 (2.4%) participants withdrew after adverse events. Equivalence of phase III lots was demonstrated for 11 of 12 pairwise comparisons. One of three comparisons for serotype 2 was not statistically equivalent. GMTs for serotype 2 in phase III lots were close to each other (65.9, 44.1 and 58.1, respectively).

CONCLUSIONS

Phase III lots can be produced in a consistent manner with predictable immune response and acceptable safety profile similar to previously characterised phase II lots. The phase III lots may be considered as not clinically different as statistical equivalence was shown for serotypes 1, 3 and 4 across the phase III lots. For serotype 2, although equivalence was not shown between two lots, the GMTs observed in the phase III lots were consistently higher than those for the phase II lot. As such, in our view, biological equivalence for all serotypes was demonstrated.

First Experience of Concomitant Vaccination Against Dengue and MMR in Toddlers

BACKGROUND

Dengue is a major public health concern in pediatric populations in endemic regions. A recombinant, live, attenuated, tetravalent dengue vaccine (CYD-TDV) is under development for the control of dengue with a 3-dose (0-6-12 month) vaccination schedule.

METHODS

In this controlled phase II trial conducted in the Philippines, 210 toddlers aged 12-15 months were randomized to 4 groups: 3 groups received the CYD-TDV vaccination schedule and a measles, mumps and rubella (MMR) vaccine given either concomitantly with the first CYD-TDV dose or 1 month earlier; 1 group received 3 active control vaccines. Safety and reactogenicity were assessed after each dose. Immunogenicity was assessed 30 days after vaccinations using the plaque reduction neutralization test against dengue and enzyme-linked immunosorbent assay methods against MMR antigens.

RESULTS

Injection site and systemic reactions occurred at similar rates across CYD-TDV groups, except for fever, which was more frequent after CYD-TDV and MMR coadministration (28.8%) compared with other groups (12-20%). Reactogenicity did not increase with subsequent CYD-TDV injections. There were no safety issues with the study vaccine. CYD-TDV achieved a balanced antibody response to all 4 dengue serotypes across the study groups, with geometric mean titers in the range of 105-124, 147-213, 311-387 and 127-160 for serotypes 1, 2, 3 and 4, respectively. CYD-TDV coadministration did not affect MMR immunogenicity (≥95% seroprotection against MMR) and vice versa.

CONCLUSIONS

The CYD-TDV has an acceptable safety and immunogenicity profile in toddlers and when coadministered with MMR.

Prospective cohort study with active surveillance for fever in four dengue endemic countries in Latin America

To prepare for a Phase III dengue vaccine efficacy trial, 20 investigational sites were selected for this observational study to identify dengue infections in a closed cohort (N = 3,000 children 9-16 years of age). Of 255 acute febrile episodes experienced by 235 children, 50 (21.3%) were considered serologically probable dengue, and 18 (7.7%) were considered virologically confirmed (i.e., dengue NS1 antigen positive) dengue cases. Considering the disease-free and at-risk period from study start to onset of symptoms, the overall incidence density of acute febrile episodes was 17.7 per 100 person-years of follow-up, ranging from 15.3 in Colombia to 22.0 in Puerto Rico. This study showed that all sites were capable of capturing and following up acute febrile episodes within a specific timeframe among the established cohort and to detect dengue cases.