JNK pathway restricts DENV2, ZIKV and CHIKV infection by activating complement and apoptosis in mosquito salivary glands

Arbovirus infection of Aedes aegypti salivary glands (SGs) determines transmission. However, there is a dearth of knowledge on SG immunity. Here, we characterized SG immune response to dengue, Zika and chikungunya viruses using high-throughput transcriptomics. We also describe a transcriptomic response associated to apoptosis, blood-feeding and lipid metabolism. The three viruses differentially regulate components of Toll, Immune deficiency (IMD) and c-Jun N- terminal Kinase (JNK) pathways. However, silencing of the Toll and IMD pathway components showed variable effects on SG infection by each virus. In contrast, regulation of the JNK pathway produced consistent responses in both SGs and midgut. Infection by the three viruses increased with depletion of the activator Kayak and decreased with depletion of the negative regulator Puckered. Virus-induced JNK pathway regulates the complement factor, Thioester containing protein-20 (TEP20), and the apoptosis activator, Dronc, in SGs. Individual and co-silencing of these genes demonstrate their antiviral effects and that both may function together. Co-silencing either TEP20 or Dronc with Puckered annihilates JNK pathway antiviral effect. Upon infection in SGs, TEP20 induces antimicrobial peptides (AMPs), while Dronc is required for apoptosis independently of TEP20. In conclusion, we revealed the broad antiviral function of JNK pathway in SGs and showed that it is mediated by a TEP20 complement and Dronc-induced apoptosis response. These results expand our understanding of the immune arsenal that blocks arbovirus transmission.

Arboviral diseases caused by dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV) viruses are responsible for large number of death and debilitation around the world. These viruses are transmitted to humans by the mosquito vector, Aedes aegypti. During the bites, infected salivary glands (SGs) release saliva containing viruses, which initiate human infection. As the tissue where transmitted viruses are produced, SG infection is a key determinant of transmission. To bridge the knowledge gap in vector-virus molecular interactions in SGs, we describe the transcriptome after DENV, ZIKV and CHIKV infection using RNA-sequencing and characterized the immune response in this tissue. Our study reveals the broad antiviral function of c-Jun N-terminal kinase (JNK) pathway against DENV, ZIKV and CHIKV in SGs. We further show that it is mediated by the complement system and apoptosis, identifying the mechanism. Our study adds the JNK pathway to the immune arsenal that can be harnessed to engineer refractory vectors.

A predominant dengue virus-1 endemic strain and the vector competence of Aedes albopictus from Guangzhou City, China

INTRODUCTION

Dengue has been a serious public health burden and dengue virus-1 (DENV-1) is the predominant strain in Guangdong province, China. Differences exist in the transmission dynamics amongAedes albopictus and DENV in different geographical regions. However, little is known about the vector competence of indigenous Aedes albopictus for the predominant dengue strain in Guangdong province, China.

METHODOLOGY

In this study, the field-derivedAedes albopictus collected from Guangzhou city, Guangdong province were infected with the predominant DENV endemic strain DENV-1 GZ201401 by feeding on serially diluted artificial infectious blood or infected suckling mice. DENV-infected mosquitoes were evaluated for viral load at five-time intervals in three tissues, the head, body and legs using reverse transcription-quantitative PCR (RT-qPCR). The vertical transmission of DENV in Ades albopictus was also analysed. Suckling mice were used to assess the transmission of DENV by Aedes albopictus.

RESULTS

There was no difference in infection rates between mosquitoes infected by infected suckling mice or by artificial infectious blood. The proportion of DENV-1 positive mosquitoes increased over time after an infectious blood meal, but there was no difference in the positive rate beyond 7days after the blood meal. The positive rate of DENV-1 infected mosquitoes increased with the DENV titer in the blood meal. Most of the infections the infected mosquitoes were disseminated more than 7 days after imbibing the artificial infectious blood. The median infective doses (MID50) at 7,14,21 and 28 days after artificial infectious blood meal [7, 14, 21 and 28 days post-infection (dpi)] were 7.86 × 10⁷, 1.57 × 10⁷, 6.39 × 10⁶ and 4.96 × 10⁶ TCID₅₀ (50% tissue culture infective dose)/ml, respectively. The mosquitoes can spread DENV-1 GZ201401 to hosts as early as 3 dpi. The vertical transmission of DENV-1 was documented with a cumulative rate of 17.61%.

CONCLUSION

Our results demonstrated that Aedes albopictus mosquitoes are competent vectors for DENV-1, and are capable of maintaining autochthonous dengue outbreaks in Guangdong province, China, which may have been promoted by vertical transmission.

Is asthma a protective factor for dengue fever? In vitro experiment and nationwide population-based cohort analysis

BACKGROUND

Dengue fever (DF) is the most rapidly spreading mosquito-borne viral disease. Practical vaccines or specific therapeutics are still expected. Environmental factors and genetic factors affect the susceptibility of Dengue virus (DV) infection. Asthma is a common allergic disease, with house dust mites (HDMs) being the most important allergens. Asthmatic patients are susceptible to several microorganism infections.

METHODS

A nationwide population-based cohort analysis was designed to assess whether to determine whether asthma can be a risk factor for DF.

RESULTS

Unexpectedly, our data from a nationwide population-based cohort revealed asthmatic patients are at a decreased risk of DF. Compared to patients without asthma, the hazard ratio (HR) for DF in patients with asthma was 0.166 (95% CI: 0.118-0.233) after adjustment for possible confounding factors. In the age stratification, the adjusted HR for DF in young adult patients with asthma was 0.063. Dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) of dendritic cells (DCs) is an important entry for DV. Through another in vitro experiment, we found that HDM can diminish surface expression of DC-SIGN in monocyte-derived DCs and further decrease the cellular entry of DV.

CONCLUSIONS

Decreased DC-SIGN expression in DCs of allergic asthmatic patient may be one of many factors for them to be protected against DF. This could implicate the potential for DC-SIGN modulation as a candidate target for designing therapeutic strategies for DF.

Dependency of Vaccine Efficacy on Preexposure and Age: A Closer Look at a Tetravalent Dengue Vaccine

Background

A recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) was licensed for children aged ≥9 years in a few countries, but the dependence of vaccine efficacy on baseline immunity status and age groups has not been fully characterized.

Methods

Combining the 2 phase 3 trials CYD14 and CYD15, we estimated the vaccine efficacy for each of the 4 serotypes of dengue virus (DENV), as well as all serotypes combined, simultaneously stratified by baseline immunity status and age group, while accounting for uncertainty in the baseline immunity status of subjects.

Results

Baseline seropositive subjects showed high efficacy for all serotypes: 70.2% (95% confidence interval [CI], 57.4%-80.1%) for dengue serotype 1 (DENV-1), 67.9% (95% CI, 49.9%-82.0%) for DENV-2, 77.5% (95% CI, 64.3%-90.2%) for DENV-3, 89.9% (95% CI, 79.8%-99.9%) for DENV-4, and 75.4% (95% CI, 68.3%-81.6%) overall. In contrast, baseline seronegative subjects showed moderate efficacy against DENV-4 (51.2% [95% CI, 20.0%-72.8%]) but no significant efficacy against other serotypes. Among seropositive children, the overall efficacy tended to increase with age: 35.9% (95% CI, -7.6% to 69.3%) for children ≤5 years old, 65.6% (95% CI, 40.3%-84.2%) for those 6-8 years old, 73.4% (95% CI, 62.6%-82.1%) for those 9-11 years old, and 80.6% (95% CI, 72.9%-87.3%) for those 12 years or older.

Conclusions

The CYD-TDV vaccine was highly efficacious for all dengue serotypes among children aged >5 years who have acquired baseline immunity from previous exposure. Increasing vaccine efficacy with age was not fully explained by increasing prevalence of baseline immunity with age.

C-Type Lectin-20 Interacts with ALP1 Receptor to Reduce Cry Toxicity in Aedes aegypti

Aedes aegypti is a crucial vector for human diseases, such as yellow fever, dengue, chikungunya, and Zika viruses. Today, a major challenge throughout the globe is the insufficient availability of antiviral drugs and vaccines against arboviruses, and toxins produced by Bacillus thuringiensis (Bt) are still used as biological agents for mosquito control. The use of Cry toxins to kill insects mainly depends on the interaction between Cry toxins and important toxin receptors, such as alkaline phosphatase (ALP). In this study, we investigated the function of A. aegypti C-type lectin-20 (CTL-20) in the tolerance of Cry toxins. We showed that recombinant CTL-20 protein interacted with both Cry11Aa and ALP1 by the Far-Western blot and ELISA methods, and CTL-20 bound to A. aegypti larval brush border membrane vesicles (BBMVs). Binding affinity of CTL-20 to ALP1 was higher than that of Cry11Aa to ALP1. Furthermore, the survival rate of A. aegypti larvae fed with Cry11Aa toxin mixed with recombinant CTL-20 fusion protein was significantly increased compared with that of the control larvae fed with Cry11Aa mixed with thioredoxin. Our novel results suggest that midgut proteins like CTLs may interfere with interactions between Cry toxins and toxin receptors by binding to both Cry toxins and receptors to alter Cry toxicity.

Recognizing spatial and temporal clustering patterns of dengue outbreaks in Taiwan

BACKGROUND

Dengue fever is the most common arboviral infection in humans, with viral transmissions occurring in more than 100 countries in tropical regions. A global strategy for dengue prevention and control was established more than 10 years ago. However, the factors that drive the transmission of the dengue virus and subsequent viral infection continue unabated. The largest dengue outbreaks in Taiwan since World War II occurred in two recent successive years: 2014 and 2015.

METHODS

We performed a systematic analysis to detect and recognize spatial and temporal clustering patterns of dengue incidence in geographical areas of Taiwan, using the map-based pattern recognition procedure and scan test. Our aim was to recognize geographical heterogeneity patterns of varying dengue incidence intensity and detect hierarchical incidence intensity clusters.

RESULTS

Using the map-based pattern recognition procedure, we identified and delineated two separate hierarchical dengue incidence intensity clusters that comprise multiple mutually adjacent geographical units with high dengue incidence rates. We also found that that dengue incidence tends to peak simultaneously and homogeneously among the neighboring geographic units with high rates in the same cluster.

CONCLUSION

Beyond significance testing, this study is particularly desired by and useful for health authorities who require optimal characteristics of disease incidence patterns on maps and over time. Among the integrated components for effective prevention and control of dengue and dengue hemorrhagic fever are active surveillance and community-based integrated mosquito control, for which this study provides valuable inferences. Effective dengue prevention and control programs in Taiwan are critical, and have the added benefit of controlling the potential emergence of Zika.

Imported cases and minimum temperature drive dengue transmission in Guangzhou, China: evidence from ARIMAX model

Dengue is the fastest spreading mosquito-transmitted disease in the world. In China, Guangzhou City is believed to be the most important epicenter of dengue outbreaks although the transmission patterns are still poorly understood. We developed an autoregressive integrated moving average model incorporating external regressors to examine the association between the monthly number of locally acquired dengue infections and imported cases, mosquito densities, temperature and precipitation in Guangzhou. In multivariate analysis, imported cases and minimum temperature (both at lag 0) were both associated with the number of locally acquired infections (P < 0.05). This multivariate model performed best, featuring the lowest fitting root mean squared error (RMSE) (0.7520), AIC (393.7854) and test RMSE (0.6445), as well as the best effect in model validation for testing outbreak with a sensitivity of 1.0000, a specificity of 0.7368 and a consistency rate of 0.7917. Our findings suggest that imported cases and minimum temperature are two key determinants of dengue local transmission in Guangzhou. The modelling method can be used to predict dengue transmission in non-endemic countries and to inform dengue prevention and control strategies.

Characterization of the adult Aedes aegypti early midgut peritrophic matrix proteome using LC-MS

The Aedes aegypti mosquito is the principal vector of arboviruses such as dengue, chikungunya, yellow fever, and Zika virus. These arboviruses are transmitted during adult female mosquito bloodfeeding. While these viruses must transverse the midgut to replicate, the blood meal must also reach the midgut to be digested, absorbed, or excreted, as aggregation of blood meal metabolites can be toxic to the female mosquito midgut. The midgut peritrophic matrix (PM), a semipermeable extracellular layer comprised of chitin fibrils, glycoproteins, and proteoglycans, is one such mechanism of protection for the mosquito midgut. However, this structure has not been characterized for adult female Ae. aegypti. We conducted a mass spectrometry based proteomic analysis to identify proteins that comprise or are associated with the adult female Ae. aegypti early midgut PM. Altogether, 474 unique proteins were identified, with 115 predicted as secreted. GO-term enrichment analysis revealed an abundance of serine-type proteases and several known and novel intestinal mucins. In addition, approximately 10% of the peptides identified corresponded to known salivary proteins, indicating Ae. aegypti mosquitoes extensively swallow their own salivary secretions. However, the physiological relevance of this remains unclear, and further studies are needed to determine PM proteins integral for midgut protection from blood meal derived toxicity and pathogen protection. Finally, we describe substantial discordance between previously described transcriptionally changes observed in the midgut in response to a bloodmeal and the presence of the corresponding protein in the PM. Data are available via ProteomeXchange with identifier PXD007627.

Assessing current temporal and space-time anomalies of disease incidence

Approaches used to early and accurately characterize epidemiologic patterns of disease incidence in a temporal and spatial series are becoming increasingly important. Cluster tests are generally designed for retrospective detection of epidemiologic anomalies in a temporal or space-time series. Timely identification of anomalies of disease or poisoning incidence during ongoing surveillance or an outbreak requires the use of sensitive statistical methods that recognize an incidence pattern at the time of occurrence. This report describes 2 novel analytical methods that focus on detecting anomalies of incidence at the time of occurrence in a temporal and space-time series. The first method describes the paucity of incidence at the time of occurrence in an ongoing surveillance and is designed to evaluate whether a decline in incidence occurs on the single current day or during the most recent few days. The second method provides an overall assessment of current clustering or paucity of incidence in a space-time series, allowing for several space regions. We illustrate the application of these methods using a subsample of a temporal series of data on the largest dengue outbreak in Taiwan in 2015 since World War II and demonstrate that they are useful to efficiently monitor incoming data for current clustering and paucity of incidence in a temporal and space-time series. In light of the recent global emergence and resurgence of Zika, dengue, and chikungunya infection, these approaching for detecting current anomalies of incidence in the ongoing surveillance of disease are particularly desired and needed.

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.

Progress and Works in Progress: Update on Flavivirus Vaccine Development

Most areas of the globe are endemic for at least one flavivirus, putting billions at risk for infection. This diverse group of viral pathogens causes a range of manifestations in humans from asymptomatic infection to hemorrhagic fever to encephalitis to birth defects and even death. Many flaviviruses are transmitted by mosquitos and have expanded in geographic distribution in recent years, with dengue virus being the most prevalent, infecting approximately 400 million people each year. The explosive emergence of Zika virus in Latin America in 2014 refocused international attention on this medically important group of viruses. Meanwhile, yellow fever has caused major outbreaks in Africa and South America since 2015 despite a reliable vaccine. There is no vaccine for Zika yet, and the only licensed dengue vaccine performs suboptimally in certain contexts. Further lessons are found when considering the experience with Japanese encephalitis virus, West Nile virus, and tickborne encephalitis virus, all of which now have protective vaccination in human or veterinary populations. Thus, vaccination is a mainstay of public health strategy for combating flavivirus infections; however, numerous challenges exist along the path from development to delivery of a tolerable and effective vaccine. Nevertheless, intensification of investment and effort in this area holds great promise for significantly reducing the global burden of disease attributable to flavivirus infection.

Peridomestic Aedes malayensis and Aedes albopictus are capable vectors of arboviruses in cities

BACKGROUND

Dengue and chikungunya are global re-emerging mosquito-borne diseases. In Singapore, sustained vector control coupled with household improvements reduced domestic mosquito populations for the past 45 years, particularly the primary vector Aedes aegypti. However, while disease incidence was low for the first 30 years following vector control implementation, outbreaks have re-emerged in the past 15 years. Epidemiological observations point to the importance of peridomestic infection in areas not targeted by control programs. We investigated the role of vectors in peri-domestic areas.

METHODS

We carried out entomological surveys to identify the Aedes species present in vegetated sites in highly populated areas and determine whether mosquitoes were present in open-air areas frequented by people. We compared vector competence of Aedes albopictus and Aedes malayensis with Ae. aegypti after oral infection with sympatric dengue serotype 2 and chikungunya viruses. Mosquito saliva was tested for the presence of infectious virus particles as a surrogate for transmission following oral infection.

RESULTS

We identified Aedes albopictus and Aedes malayensis throughout Singapore and quantified their presence in forested and opened grassy areas. Both Ae. albopictus and Ae. malayensis can occupy sylvatic niches and were highly susceptible to both arboviruses. A majority of saliva of infected Ae. malayensis contained infectious particles for both viruses.

CONCLUSIONS

Our study reveals the prevalence of competent vectors in peri-domestic areas, including Ae. malayensis for which we established the vector status. Epidemics can be driven by infection foci, which are epidemiologically enhanced in the context of low herd immunity, selective pressure on arbovirus transmission and the presence of infectious asymptomatic persons, all these conditions being present in Singapore. Learning from Singapore's vector control success that reduced domestic vector populations, but has not sustainably reduced arboviral incidence, we suggest including peri-domestic vectors in the scope of vector management.

Lack of Durable Cross-Neutralizing Antibodies Against Zika Virus from Dengue Virus Infection

Cross-reactive antibodies elicited by dengue virus (DENV) infection might affect Zika virus infection and confound serologic tests. Recent data demonstrate neutralization of Zika virus by monoclonal antibodies or human serum collected early after DENV infection. Whether this finding is true in late DENV convalescence (>6 months after infection) is unknown. We studied late convalescent serum samples from persons with prior DENV or Zika virus exposure. Despite extensive cross-reactivity in IgG binding, Zika virus neutralization was not observed among primary DENV infections. We observed low-frequency (23%) Zika virus cross-neutralization in repeat DENV infections. DENV-immune persons who had Zika virus as a secondary infection had distinct populations of antibodies that neutralized DENVs and Zika virus, as shown by DENV-reactive antibody depletion experiments. These data suggest that most DENV infections do not induce durable, high-level Zika virus cross-neutralizing antibodies. Zika virus-specific antibody populations develop after Zika virus infection irrespective of prior DENV immunity.

Dengue virus serological prevalence and seroconversion rates in children and adults in Medellin, Colombia: implications for vaccine introduction

BACKGROUND

Dengue is an important public health problem worldwide. A vaccine has recently been licensed in some countries of Latin America and Asia. Recommendations for dengue vaccine introduction include endemicity and a high serological prevalence of dengue in the territories considering its introduction.

METHODS

A community-based survey was conducted to estimate dengue seroprevalence and age-specific seroconversion rates in a community in Medellin, Colombia, using a dengue serological test (IgG indirect ELISA). Residents were selected at random and were first screened for dengue infection; they were then followed over 2.5 years.

RESULTS

A total of 3684 individuals aged between 1 and 65 years participated in at least one survey. The overall dengue seroprevalence was 61%, and only 3.3% of seropositive subjects self-reported a past history of dengue. Among dengue virus (DENV)-naïve subjects with more than two visits (n=1002), the overall seroconversion rate was 8.7% (95% confidence interval 7.3-10.4) per 1000 person-months, over the study period. Overall, the mean age of DENV prevalent subjects was significantly higher than the mean age of seroconverted subjects. Specifically, DENV seropositivity over 70% was observed in participants over 21 years old. Serotype-specific plaque-reduction neutralization tests (PRNT) revealed that all four dengue serotypes were circulating, with DENV4 being most prevalent.

CONCLUSIONS

These laboratory-based findings could inform dengue vaccine decisions, as they provide age-specific seroprevalence and seroconversion data, evidencing permanent and ongoing dengue transmission in the study area. This study provides evidence for the existing rates of secondary and heterotypic responses, presenting a challenge that must be addressed adequately by the new vaccine candidates.

Resveratrol treatment reveals a novel role for HMGB1 in regulation of the type 1 interferon response in dengue virus infection

Dengue is one of the most significant mosquito-borne virus diseases worldwide, particularly in tropical and subtropical regions. This study sought to examine the antiviral activity of resveratrol (RESV), a phytoalexin secreted naturally by plants, against dengue virus (DENV) infection. Our data showed that RESV inhibits the translocation of high mobility group box 1 (HMGB1), a DNA binding protein that normally resides in the nucleus, into the cytoplasm and extracellular milieu. HMGB1 migrates out of the nucleus during DENV infection. This migration is inhibited by RESV treatment and is mediated by induction of Sirt1 which leads to the retention of HMGB1 in the nucleus and consequently helps in the increased production of interferon-stimulated genes (ISGs). Nuclear HMGB1 was found to bind to the promoter region of the ISG and positively regulated the expression of ISG. The enhanced transcription of ISGs by nuclear HMGB1 thus contributes to the antiviral activity of RESV against DENV. To the best of our knowledge, this is the first report to demonstrate that RESV antagonizes DENV replication and that nuclear HMGB1 plays a role in regulating ISG production.

Prevention and control of dengue-the light at the end of the tunnel

Advances in the development of new dengue control tools, including vaccines and vector control, herald a new era of desperately needed dengue prevention and control. The burden of dengue has expanded for decades, and now affects more than 120 countries. Complex, large-scale global forces have and will continue to contribute to the expansion of dengue, including population growth, unplanned urbanisation, and suboptimal mosquito control in urban centres. Although no so-called magic bullets are available, there is new optimism following the first licensure of a dengue vaccine and other promising vaccine candidates, and the development of novel vector control interventions to help control dengue and other expanding mosquito-borne diseases such as Zika virus. Implementation of effective and sustainable immunisation programmes to complement existing methods will add complexity to the health systems of affected countries, which have varying levels of robustness and maturity. Long-term high prioritisation and adequate resources are needed. The way forward is full commitment to addressing a complex disease with a set of solutions integrating vaccination and vector control methods. A whole systems approach is thus needed to integrate these various approaches and strategies for controlling dengue within the goal of universal health coverage. The ultimate objective of these interventions will be to reduce the disease burden in a sustainable and equitable manner.

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.

Estimating the public health importance of the CYD-tetravalent dengue vaccine: Vaccine preventable disease incidence and numbers needed to vaccinate

BACKGROUND

To evaluate the potential public health impact of the live attenuated tetravalent Sanofi Pasteur dengue vaccine (CYD-TDV) we analyzed data from the reported clinical trials to calculate vaccine preventable disease incidence (VPDI) and number needed to vaccinate (NNV) based on the licensure indication for persons age 9 years and above.

METHODS

VPDI is defined as incidence in an unvaccinated population X vaccine efficacy (VE), and thus incorporates both VE and the underlying burden of disease. NNV was calculated as 100,000 divided by VPDI divided by 2-year length of study. We compared these values to data for three newer vaccines that are currently integrated into some national immunization programs in Asia and Latin America, namely pneumococcal conjugate, Haemophilus influenzae type b, and rotavirus vaccines.

RESULTS

In the Asian-Pacific trial, in the first 25 months after the first dose of the dengue vaccine, CYD-TDV prevented annually 2639 cases of virologically confirmed dengue for every 100,000 persons vaccinated, for an NNV of 18. In the Latin American trial, given the overall lower annual dengue incidence compared to Asia, VPDI was 1707, and NNV 28. For the Asian-Pacific and Latin American studies, the VPDIs for hospitalized virologically confirmed disease at the trials' end were 638 and 239 per 100,000 population per year, respectively, with NNVs of 75 and 201. VPDI for confirmed dengue hospitalization was higher than that for Hib vaccine against Hib meningitis or all cause severe pneumonia while lower than that for rotavirus vaccine against severe rotavirus gastroenteritis.

CONCLUSIONS

Our analysis found that the CYD-TDV dengue vaccine had favorable VPDI and NNV, also when compared to existing vaccines used in Latin America and Asia. VPDI and NNV varied by serotype distribution, extent of prior dengue exposure (baseline seroprevalence) and country. These findings will help policy-makers decide where and how to introduce this vaccine post-licensure.

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.