Leitthema

Bundesgesundheitsbl 2020 · 63:40–44 Annelies Wilder-Smith1,2 https://doi.org/10.1007/s00103-019-03060-3 1 Department of Disease Control, London School of Hygiene and Tropical Medicine, London, UK Published online: 29 November 2019 2 Heidelberg Institute of Global Health, University of Heidelberg, Heidelberg, Germany © Springer-Verlag GmbH Deutschland, ein Teil von Springer Nature 2019 Dengue development: status and future

Introduction Rationale for a dengue vaccine serotypes. As a tetravalent immune re- sponse is desired, when a mixture of all Dengue is globally the most frequent ar- According to modeling estimates, about four serotypes in a tetravalent live at- boviral disease, present in more than 128 50–100 million dengue cases occur every tenuated vaccine is given, each compo- countries in the tropics and subtropics year [10]. Te incidence of dengue has nent would need to independently result and poised to increase even further in increased greatly, with the number of in four different monotypic immune re- terms of incidence and continued geo- cases more than doubling every decade, sponses that are solid to each serotype. graphic expansion [1, 2], thereby also af- from 8.3 million (3.3–17.2 million) ap- Tis has, unfortunately, proven to be dif- fecting international travelers [3, 4]. Te parent cases in 1990 to 58.4 million ficult to achieve. four serotypes belong to the (23.6–121.9 million) apparent cases in family of Flaviviridae and are genetically 2013, responsible for 1.14 million disabil- Dengue vaccine development distinct but still closely related. Infec- ity-adjusted life-years [10]. In dengue- tion with any of the four dengue virus endemic countries, approximately 10% Despite more than 30 years of efforts serotypes may be asymptomatic or may offebrileepisodesinchildrenandado- using various vaccine platforms includ- result in clinical manifestations ranging lescents are due to dengue, with a higher ing inactivated, DNA, and live , from a mild undifferentiated febrile syn- incidence in Asia (4.6 episodes per 100 only live attenuated vaccines have en- drome to severe dengue. Severe dengue person-years) compared to Latin Amer- tered phase 3 trials. Tree live attenu- is characterized by plasma leakage, hem- ica (2.9 episodes per 100 person-years); ateddenguevaccinesarenowinlate-stage orrhagic tendencies, organ failure, shock, the percentage of dengue re- development, with one candidate having and, occasionally,death[5]. Patientswith quiring hospitalization was 19% in Asia completed phase 3 trials including long- a second dengue with a dengue versus 11% in Latin America [11]. Many term follow-up of 5 years: CYD-TDV serotype different from the first are at dengue infections lead to hospitaliza- by Sanofi Pasteur, Lyon, France, with the increased risk for severe dengue. Te tions, which can overwhelm weak health trade name of Dengvaxia. hallmark of severe dengue is capillary carestructures, inparticularduringtimes leakage leading to shock and, if not man- of outbreaks. Given the unpredictability CYD-TDV dengue vaccine aged well, death. Te pathomechanism of outbreaks, the increasing magnitude of severe dengue is still poorly under- and frequency of such outbreaks, and CYD-TDV, a tetravalent live attenuated stood, although the most plausible hy- the current lack of highly effective and vaccine with a yellow fever 17D back- pothesisisantibody-dependentenhance- sustainable vector-control interventions, bone, is the first dengue vaccine to be li- ment in secondary infections [6]. Be- there is a clear indication for a dengue censed. Phase 3 trials revealed a vaccine cause effective vector-control measures vaccine for endemic populations. efficacy that depended on age, serosta- are not scalable or sustainable, commu- tus, and serotype but also showed a pop- nity-based approaches have led to mixed Challenges and hurdles in ulation-level benefit [13]. Interference results [7, 8], and promising novel strate- the development of dengue manifested by asymmetric immunolog- gies such as Wolbachia are still under de- vaccines ical responses to the mixtures of four velopment [9], a dengue vaccine would dengue vaccine viruses was recognized appear to be the best intervention. Te Severaldifficultieshave hampered the de- as a possible reason for this varied vac- purpose of this review is to elaborate on velopment of a dengue vaccine. One cine performance [14]. Post hoc retro- the first licensed dengue vaccine and re- challenge is the lack of an appropriate spective analyses of the long-term safety viewsecond-generationdenguevaccines, animal model and poor knowledge of data using a novel nonstructural protein both in the context of endemic popula- correlates, both for protection and dis- (NS1) antibody assay revealed an excess tions as well as international travelers. ease enhancement [12]. But the biggest risk of severe dengue in those who were hurdle is the interaction among the four seronegative at baseline, which means

40 Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz 1 · 2020 those who were dengue-naïve at the time cination screening strategy [22]. In May and phase 2 clinical trials, with high of administration of the first dose [15]. 2019, the U.S. Food and Drug Adminis- titers of neutralizing antibody to all four Tisincreasedriskwasobservedstart- tration (FDA) approved CYD-TDV for serotypes in nonhuman primates and ing from 30 months afer administration use in seropositive individuals 9–16 years humans, including cross-reactive T-cell- of the first dose. Te reasons for the of age living in endemic areas of the mediated responses that may be neces- excess cases are not fully understood, United States. Te European Medicines sary for broad protection against dengue but a plausible hypothesis is that Deng- Agency also endorsed the use of this vac- fever [25, 26]. Te vaccine efficacy is vaxia may trigger an immune response cine in seropositive individuals only. currently being tested in approximately to dengue in seronegative persons that Te World Health Organization has 20,000 recipients in phase 3 trials in predisposes them to a higher risk of se- published guidance on evaluating the Asia and Latin America using a two- vere disease, analogous to what is seen quality, safety, and efficacy of live at- dose regimen given 3 months apart. in natural secondary dengue infections. tenuated dengue tetravalent vaccines, Efficacy data for the first 18 months are In other words, it is plausible that Deng- including the need for baseline blood imminent. vaxia results in a “primary-like” silent samples from all participants for a priori Te other tetravalent live attenuated infection (which live attenuated vaccines analysis plans stratified by serostatus, as dengue vaccine was developed by the U.S. ofen elicit) [16]. A subsequent infection well as long-term follow-up for 3–5 years National Institutes of Health (NIH) and with the first true wild-type dengue virus afer the first dose [23]. Tis document is currently in a phase 3 trial in Brazil, but would then be a “secondary-like”, clin- will guide vaccine developers in trial itwasalsolicensedtoMerckandvarious ically more severe dengue illness. It is design and facilitate regulatory review other vaccine manufacturers for further not the vaccine itself that causes excess to enable broader public health rec- development outside Brazil. Tis vac- cases, but rather the vaccine’s induction ommendations for second-generation cine consists of three full-length dengue of an immune status that increases the dengue vaccines. Indeed, the phase 3 virus (DENV) serotypes attenuated by ′ risk that subsequent infections will be efficacy trials of the two second-genera- one or more deletions in the 3 untrans- more severe. tion dengue vaccines have incorporated lated region with DEN1Δ30, DEN2Δ30, Despite licensure in 20 dengue-en- all these requirements. Furthermore, and DEN4Δ30, while the fourth com- demic countries to date, CYD-TDV has there is a need for the development ponent is a chimeric virus in which the been introduced in only two subnational of standardized end points for vaccine prM and E proteins of DENV-2 replace public health programs: those in the and other interventional trials, includ- thoseofDENV-4intheDEN4Δ30back- Philippines and in Brazil. Afer a me- ing the need for subsequent validation ground[27]. Tisvaccineperformedwell dia release in November 2017 about the with prospective data sets [24]. Te and was safe in phase 1 and phase 2 tri- safety concern for seronegative persons, complexity of developing moderate dis- als [28]. A single dose induced robust the Philippines decided to suspend its ease research end points for dengue is tetravalent antibody and cellular T-cell program, while Brazil completed its pro- particularly challenging. responsesandresultedin100%efficacyin grambuthasnotexpandedit.Temedia ahumanchallengestudy[29]. Tecapac- release resulted in a major public outcry Second-generation dengue ity to elicit CD4+ cell responses closely in the Philippines, with heightened anx- vaccines mirrored those observed in a population iety and lack of confidence around vac- associated with natural immunity [30]. cines in general [17], which led to the Two live attenuated dengue vaccines are Teadvantagesofthesesecond-gener- subsequent resurgence of measles in the nowinphase3trials.Onesuchliveatten- ationdenguevaccinesaretheinclusionof Philippines, reflecting the global resur- uated dengue vaccine is being developed NS proteins of the dengue backbone and gence of measles [18–20]. Communi- by Takeda: DENVax vaccine consists more convenient dosing, with reduced cation around the introduction of any of an attenuated DENV-2 (DEN2-PDK- numbers of doses needed: While Deng- newvaccine, butespeciallythosevaccines 53), whereby three chimeric viruses con- vaxia is licensed for three doses 6 months with partial efficacy or complex vaccine taining the prM and envelope proteins of apart, the Takeda vaccine is currently be- performance, needs to be improved to DENV-1, DENV-3, and DENV-4 are in- ing considered for two doses 3 months avoid public distrust and lack in vaccine serted into the DEN2-PDK-53 backbone. apart and the NIH vaccine for a sin- confidence. Te difference from Dengvaxia, there- gle dose. Whether these second-genera- Te World Health Organization rec- fore, isthepresenceofnonstructural(NS) tion vaccines will provide balanced high ommends that for countries considering proteins due to the DENV2 backbone. protection against all four serotypes and CYD-TDV as part of their Te conserved NS proteins within the thus overcome the serostatus-dependent dengue-control program, a prevaccina- dengue backbone may well be required problemofCYD-TDVremainsunknown tion screening strategy is recommended to generate T-cell-mediated responses to and can be addressed only by the long- so that only dengue-seropositive persons dengue infection, and antibodies against term results of the pending phase 3 trials. are vaccinated [21]. Te challenge is now NS1 are associated with cross-protective to urgently develop and license rapid di- humoral immune responses [25]. Tis agnostic tests to support such a prevac- vaccine has performed well in phase 1

Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz 1 · 2020 41 Abstract · Zusammenfassung

Dengue vaccines for travelers Bundesgesundheitsbl 2020 · 63:40–44 https://doi.org/10.1007/s00103-019-03060-3 © Springer-Verlag GmbH Deutschland, ein Teil von Springer Nature 2019 Many dengue-endemic countries are commonly visited travel destinations, A. Wilder-Smith and therefore dengue has become a fre- Dengue vaccine development: status and future quent cause of febrile illness among international travelers [31]. An increase Abstract in hospitalizations and health care visits Dengue, the most common arbovirus, to facilitate prevaccination screening. Two represents an increasingly significant cause of second-generation dengue vaccine candida- for dengue has been seen in American morbidity worldwide, including in travelers. tes, both also live attenuated recombinant [32] and European travelers [33, 34]. After decades of research, the first dengue vaccines in late-stage development, may GeoSentinel is an international network vaccine was licensed in 2015: CYD-TDV, not present the same limitations because of of travel medicine providers [35]thathas a tetravalent live with differences in the backbone used, but results also reported an increase in dengue over a backbone. Recent of phase 3 trials need to be available before analyses have shown that vaccine perfor- firm conclusions can be drawn. the past decade [36]. Dengue can affect mance is dependent on serostatus. In those Dengue is increasingly frequent in travelers, tourists, business travelers, expatriates who have had a previous dengue infection, but the only licensed dengue vaccine to date [37, 38], pilgrims [40], and migrants, i.e., who are seropositive, the efficacy is can be used only in seropositive individuals. including those visiting friends and rel- high and the vaccine is safe. However, in However, the vast majority of travelers are atives [39], and can affect both adults seronegative vaccinees, approximately seronegative. Furthermore, the primary series 3 years after vaccination the vaccine increases of three doses given 6 months apart renders and children [4, 41, 42]. Interruption the risk of developing severe dengue when this vaccine difficult in the travel medicine of travel, premature return, hospital- the individual experiences a natural dengue context. ization during or afer travel, and out- infection. of-pocket expenses are the result [43]. The World Health Organization recommends Keywords With an incidence of about 1–5% for that this vaccine be administered only to Severedengue·CYD-TDV·Antibody- seropositive individuals. Current efforts are dependent enhancement · Travelers · Live travelers to dengue-endemic countries underway to develop rapid diagnostic tests attenuated chimeric dengue vaccine [31], dengue is much more frequent than many of the other travel-associated vaccine-preventable diseases, such as Entwicklung von Impfstoffen gegen Dengue: aktueller Stand und hepatitis A, yellow fever, and Japanese Zukunft encephalitis [44, 45]. Vaccination would be of clear benefit to travelers, but the Zusammenfassung benefit versus risk needs to be clearly Das Dengue-Virus, das am meisten verbreitete beide ebenfalls attenuierte rekombinante Lebendimpfstoffe, befinden sich in der weighed [46]. Although vaccination is Arbovirus, stellt weltweit eine zunehmende Ursache für Morbidität dar, auch bei Spätphase der Entwicklungspipeline und now licensed in Europe by the European Reisenden. Nach jahrzehntelanger Forschung könnten aufgrund der Unterschiede der Medicines Agency and in the United wurde 2015 der erste Impfstoff gegen verwendeten „backbones“ nicht dieselben States by the FDA, and is also licensed in Dengue-Fieber zugelassen: CYD-TDV, ein Limitierungen aufweisen; es müssen aber die Australia, it has not yet been endorsed tetravalenter, attenuierter Lebendimpfstoff Ergebnisse der Phase-3-Studien abgewartet werden, um dies sicher beurteilen zu können. for the travel medicine indication. Fur- auf Basis des Gelbfieber-Impfvirus („back- bone“). Neuste Analysen haben gezeigt, Dengue-Fieber tritt immer häufiger bei thermore, the only currently licensed dass die Performance des Impfstoffs vom Reisenden auf. Die überwiegende Mehrheit dengue vaccine, CYD-TDV, should be Serostatus abhängig ist. Bei Menschen, die der Reisenden ist jedoch seronegativ, weshalb used only in seropositive travelers [47]. bereits eine Dengue-Infektion hatten und bei ihnen der bisher einzige zugelassene Most travelers, however, are seronegative seropositiv sind, ist die Wirksamkeit hoch Impfstoff gegen Dengue-Fieber nicht eingesetzt werden kann. Darüber hinaus [48]. Furthermore, the dosing schedule und der Impfstoff sicher. Bei seronegativen Impflingen erhöht der Impfstoff jedoch sind für die Grundimmunisierung drei of three doses 6 months apart for CYD- im Fall einer nachfolgenden Dengue- Impfdosen nach dem Schema 0-6-12 Monate TDV renders the use of such a vaccine Wildvirusinfektion das Risiko für eine schwere erforderlich, wodurch der Einsatz dieses difficult in the travel medicine context. Dengue-Erkrankung etwa 3 Jahre nach der Impfstoffes im reisemedizinischen Kontext A safe and efficacious vaccine that can Impfung. Die Weltgesundheitsorganisation schwierig ist. be used regardless of serostatus would empfiehlt daher, den Impfstoff nur an seropositive Menschen zu verabreichen. Schlüsselwörter enhance the use of a dengue vaccine in Derzeit wird intensiv an der Entwicklung von Schweres Dengue-Fieber · CYD-TDV · travelers [49]. Travelers should be ad- Schnelltests gearbeitet, um das Screening vor Antibody-dependent enhancement · vised to take daytime personal protective der Impfung zu erleichtern. Zwei Dengue- Reisende · Attenuierter chimärer Dengue- measures against mosquito bites [50]. Impfstoffkandidaten der zweiten Generation, Lebendimpfstoff

Conclusions

Given the unpredictability of dengue out- breaks, theincreasingmagnitudeandfre-

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