5. Final thoughts

4.4. Vaccine candidates under preclinical assays

Table 6. Some DEN 80E Vaccine safety and immunogenicity studies.

Reference Lead author/

Preclinical development of a dengue tetravalent recombinant subunit vaccine: Immunogenicity and protective efficacy in nonhuman primates

160 Dengue Fever - a Resilient Threat in the Face of Innovation

Development of a recombinant tetravalent dengue virus vaccine: immunogenicity and efficacy studies

The development of recombinant subunit envelope-based vaccines to protect against dengue

virus induced disease

in mice and monkeys

year

Govindarajan et al. 2015 [51]

Coller et al. 2011 [24]

Clements et al. 2010 [23] Conclusion

clinical testing.

(2–3 months).

Overall, the subunit vaccine was demonstrated to induce strong neutralization titers resulting in protection against viremia following challenge even 8–12 months after the last vaccine dose.

The DEN-80E recombinant subunit proteins for all four dengue virus types are expressed at high levels and have been shown to maintain native-like conformation. When formulated with a variety of adjuvants the antigens are potent immunogens and induce high titer virus-neutralizing antibody responses. Furthermore, the antigens have been shown to protect against viral challenge in both mouse and nonhuman primate models. Tetravalent vaccine formulations have also been evaluated in preclinical models with no evidence of immune interference or competition between the four DEN-80E antigens being observed. These proofs of concept preclinical studies led to the advancement of a monovalent DEN1-80E vaccine candidate into

The production of recombinant dengue 80E proteins in Drosophila S2 cells that are capable of eliciting potent immune responses in mice and nonhuman primates represents a major

achievement in the effort to develop a recombinant dengue vaccine. The S2 cell expression system efficiently produces 80E from all four dengue serotypes. Our data show that co-administration of the subunits from the four serotypes results in a balanced immune response, equivalent to that observed when the four individual components are administered separately. Furthermore this response can be induced in a relatively short period of time

seen in Table 8.

There are numerous vaccine candidates that are being studied in preclinical trials, as can be

Te Pedro Kourí Tropical Medicine Institute (IPK) in collaboration with the Center for Genetic Engineering and Biotechnology (CIGB) in Cuba have led the development of various recombinant subunit vaccine candidates. One approach is based on fusion of DENV EDIII to the carrier protein p64k of Neisseria meningitidis, and this EDIII-p64k fusion protein is then expressed in E. coli. Evaluations in mice showed that monovalent vaccine candidates for all

4.4.1. EDIII-p64k fusion proteins and EDIII-capsid fusion proteins expressed in E. coli

Finally, we want to reflect on the implications of the co-circulation of the dengue virus and the Zika virus, as well as on the new indications for the use of the Dengvaxia vaccine.

First, we will analyze the fact that the appearance of the infection by the Zika virus (another flavivirus) in zones of high prevalence for dengue constitutes an interesting challenge for the development of the ideal vaccine for both viruses.

#### 5.1. Zika virus infection means new challenges in dengue vaccine development

Among pathogenic human flaviviruses, DENV and ZIKV are most closely related to each other, with 55.1–56.3% amino acid sequence identity. Zika virus is closer to dengue virus than to any of the other flaviviruses and indeed is almost close enough to think of it as a fifth serotype [10]. Accordingly, emerging literature indicates many similarities between these two viruses in terms of interactions between the virus and host immune system. For both viruses, the interferon system is the central mediator of host defense and target of a viral counterattack,


Currently, there is a high pressure to produce a vaccine against ZIKV, and in this context, the extensive serological cross-reaction between DENV and ZIKV must be considered. It is likely necessary that the vaccine be used in areas with high seroprevalence for DENV and raising de novo ZIKV-neutralizing responses in such a setting might be challenging. It is likewise possible that vaccination of DENV-naive subjects against ZIKV might promote ADE of DENV infection and, conversely, that vaccination against DENV might promote ADE of ZIKV infection. In summary, cross-reaction of antibodies to DENV with ZIKV and promotion of ADE of infection can occur due to the existing similarities between the two viruses, even though ZIKV differs in sequence identity from DENV by around 41–46% (in the sequence of the envelope protein). In this context, ZIKV could be considered a fifth member of the DENV serocomplex, a factor that must be considered in vaccine approaches to these two viruses [11]. The results of Barba-Spaeth group suggest that the epitope targeted by the EDE1 bnAbs is more adequate for developing an epitope-focused vaccine for viruses of the ZIKV/DENV super serogroup than is the FLE, which induces poorly neutralizing and strongly infection-

Current Status of Vaccines against Dengue Virus http://dx.doi.org/10.5772/intechopen.80820 163

Dengvaxia is the only vaccine licensed to date for use in humans, which is why epidemiologists, health professionals, clinical physicians, and basic researchers (virologists, immunologists, molecular biologists, etc.) should be concerned about the future of this vaccine, which has had a reverse according to the latest publications of its results, so we will end this chapter

Since April 2016, Dengvaxia has been licensed for use in 19 countries, and was recommended by the WHO Strategic Advisory Group of Experts (SAGE) on immunization to be used in regions with high endemicity, as defined by a prevalence of dengue antibodies of more than 50% in the targeted age group of people aged 9–45 years. Nevertheless, Guiar's mathematical model finds that a significant reduction of hospitalizations can be only achieved when the vaccine is directed exclusively to seropositive individuals [58]. Along this same line, this group of researchers in 2017 predicted a significant reduction in dengue virus infectionrelated hospital admissions resulting from the administration of Dengvaxia only to dengue seropositive individuals, based on the analysis of an age-structured model using the available vaccine trial data. Moreover, the researchers predicted a significant increase in the number of dengue-related admissions, over a 5-year period, if the vaccine is to be administered without previous population screening for serostatus. The take-home message is that individual serostatus is the most important feature when implementing this vaccine and that only individuals of any age who have experienced at least one dengue virus infection will benefit from vaccination [59, 60]. New data by Sanofi in November 2017 showed that Dengvaxia could increase the risk of severe dengue in people who had not been previously exposed to the virus. For any countries considering vaccination as part of their dengue control program, the WHO recommends a "prevaccination screening strategy," in which only dengue seropositive people are vaccinated. The prescreening process could be achieved by conventional serological testing for dengue virus to identify people who have had previous dengue infections. As Sanofi stated, "We are confident in Dengvaxia's safety and its proven potential to

with the following reflection based on the publications from 2016 to date.

enhancing antibodies [57].

5.2. The Dengvaxia future

Table 8. Active dengue vaccine candidates in preclinical development that have been evaluated in NHP models.

whereas complex interplays between antibody and T cell responses likely determine the outcome of infection in flavivirus immune settings [55]. Dejnirattisai et al. found that most mAbs to DENV also bound to ZIKV, yet the antibodies targeting the major linear fusion-loop epitope (FLE) did not neutralize ZIKV, whereas they showed neutralizing activity against DENV. ZIKV virus infection was found to be potently enhanced by DENV-immune plasma and mAbs to DENV, suggesting the possibility that preexisting immunity to DENV might increase ZIKV replication; thus, this data indicate that immunity to DENV might drive greater ZIKV replication and have clear implications for disease pathogenesis and future vaccine programs for ZIKV and DENV [11]. There have been safety concerns related to Dengvaxia resulting from long-term vaccine trials. In patient groups under 9 years of age, hospitalization from DENV infection was greater for vaccinated children than for the nonvaccinated control group. These findings suggest ADE of infection in DENV naive children at the start of the study trial and who had been primed by but not protected by the vaccine. Consequently, the vaccine is not licensed for use in children under 9 years of age and, furthermore, it is recommended for use only in populations with a seroprevalence of 70% or greater of prior DENV exposure in the age group to be vaccinated [56].

Currently, there is a high pressure to produce a vaccine against ZIKV, and in this context, the extensive serological cross-reaction between DENV and ZIKV must be considered. It is likely necessary that the vaccine be used in areas with high seroprevalence for DENV and raising de novo ZIKV-neutralizing responses in such a setting might be challenging. It is likewise possible that vaccination of DENV-naive subjects against ZIKV might promote ADE of DENV infection and, conversely, that vaccination against DENV might promote ADE of ZIKV infection. In summary, cross-reaction of antibodies to DENV with ZIKV and promotion of ADE of infection can occur due to the existing similarities between the two viruses, even though ZIKV differs in sequence identity from DENV by around 41–46% (in the sequence of the envelope protein). In this context, ZIKV could be considered a fifth member of the DENV serocomplex, a factor that must be considered in vaccine approaches to these two viruses [11]. The results of Barba-Spaeth group suggest that the epitope targeted by the EDE1 bnAbs is more adequate for developing an epitope-focused vaccine for viruses of the ZIKV/DENV super serogroup than is the FLE, which induces poorly neutralizing and strongly infectionenhancing antibodies [57].

## 5.2. The Dengvaxia future

whereas complex interplays between antibody and T cell responses likely determine the outcome of infection in flavivirus immune settings [55]. Dejnirattisai et al. found that most mAbs to DENV also bound to ZIKV, yet the antibodies targeting the major linear fusion-loop epitope (FLE) did not neutralize ZIKV, whereas they showed neutralizing activity against DENV. ZIKV virus infection was found to be potently enhanced by DENV-immune plasma and mAbs to DENV, suggesting the possibility that preexisting immunity to DENV might increase ZIKV replication; thus, this data indicate that immunity to DENV might drive greater ZIKV replication and have clear implications for disease pathogenesis and future vaccine programs for ZIKV and DENV [11]. There have been safety concerns related to Dengvaxia resulting from long-term vaccine trials. In patient groups under 9 years of age, hospitalization from DENV infection was greater for vaccinated children than for the nonvaccinated control group. These findings suggest ADE of infection in DENV naive children at the start of the study trial and who had been primed by but not protected by the vaccine. Consequently, the vaccine is not licensed for use in children under 9 years of age and, furthermore, it is recommended for use only in populations with a seroprevalence of 70% or greater of prior

DEN/DEN chimeric viruses, live, attenuated Chiang Mai University/

Table 8. Active dengue vaccine candidates in preclinical development that have been evaluated in NHP models.

Antigen Vaccine developer Valency under

EDIII-p64k fusion proteins and EDIII-capsid fusion proteins expressed in E. coli

Bivalent 80E-STF2 fusion proteins expressed in

Tetravalent consensus EDIII protein expressed in

Tetravalent EDIII and DENV-1 ectoM expressed from live-attenuated measles virus vector

baculovirus/insect cells

DNA vaccine prM/E expressed from plasmid vector DNA

VLP Vaccines EDIII-HBsAg VLPs or ectoE-based VLPs expressed in P. pastoris

E. coli.

162 Dengue Fever - a Resilient Threat in the Face of Innovation

vaccine

evaluation or evaluated in NHP

Tetravalent

Monovalent

IPK/CIGB Monovalent

VaxInnate Tetravalent

NHRI Tetravalent

US CDC Tetravalent

ICGEB Tetravalent

Themis Bioscience/Institut X

Mahidol X University/ NSTDA/BioNet-Asia

Pasteur

E85 expressed from single-cycle VEE virus vector Global Vaccines Tetravalent

Psoralen-inactivated DENV US NMRC Monovalent

Purified inactivated DENV WRAIR/GSK/FIOCRUZ Tetravalent

Inactivated virus (+VEE-particle adjuvant) Global Vaccines Tetravalent

DEN host range mutations Arbovax Tetravalent

DENV exposure in the age group to be vaccinated [56].

Techonological approach

Recombinant subunit vaccines

Virus-vectored vaccines

Purified inactivated virus vaccine

Purified inactivated DENV

Live-attenuated virus vaccines

Dengvaxia is the only vaccine licensed to date for use in humans, which is why epidemiologists, health professionals, clinical physicians, and basic researchers (virologists, immunologists, molecular biologists, etc.) should be concerned about the future of this vaccine, which has had a reverse according to the latest publications of its results, so we will end this chapter with the following reflection based on the publications from 2016 to date.

Since April 2016, Dengvaxia has been licensed for use in 19 countries, and was recommended by the WHO Strategic Advisory Group of Experts (SAGE) on immunization to be used in regions with high endemicity, as defined by a prevalence of dengue antibodies of more than 50% in the targeted age group of people aged 9–45 years. Nevertheless, Guiar's mathematical model finds that a significant reduction of hospitalizations can be only achieved when the vaccine is directed exclusively to seropositive individuals [58]. Along this same line, this group of researchers in 2017 predicted a significant reduction in dengue virus infectionrelated hospital admissions resulting from the administration of Dengvaxia only to dengue seropositive individuals, based on the analysis of an age-structured model using the available vaccine trial data. Moreover, the researchers predicted a significant increase in the number of dengue-related admissions, over a 5-year period, if the vaccine is to be administered without previous population screening for serostatus. The take-home message is that individual serostatus is the most important feature when implementing this vaccine and that only individuals of any age who have experienced at least one dengue virus infection will benefit from vaccination [59, 60]. New data by Sanofi in November 2017 showed that Dengvaxia could increase the risk of severe dengue in people who had not been previously exposed to the virus. For any countries considering vaccination as part of their dengue control program, the WHO recommends a "prevaccination screening strategy," in which only dengue seropositive people are vaccinated. The prescreening process could be achieved by conventional serological testing for dengue virus to identify people who have had previous dengue infections. As Sanofi stated, "We are confident in Dengvaxia's safety and its proven potential to

reduce dengue disease burden in endemic countries. We will continue to work with the international public health community and endemic countries, to ensure the best usage of the vaccine to increase protection for populations at risk of subsequent dengue infections [that are] potentially more debilitating" [61].

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Current Status of Vaccines against Dengue Virus http://dx.doi.org/10.5772/intechopen.80820 165

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