Formalin-inactivated whole virus and recombinant subunit flavivirus vaccines

Methodical Design of Viral Vaccines Based on Avant-Garde Nanocarriers: A Multi-Domain Narrative Review

The current health crisis caused by coronavirus 2019 (COVID-19) and associated pathogens emphasize the urgent need for vaccine systems that can generate protective and long-lasting immune responses. Vaccination, employing peptides, nucleic acids, and other molecules, or using pathogen-based strategies, in fact, is one of the most potent approaches in the management of viral diseases. However, the vaccine candidate requires protection from degradation and precise delivery to the target cells. This can be achieved by employing different types of drug and vaccine delivery strategies, among which, nanotechnology-based systems seem to be more promising. This entry aims to provide insight into major aspects of vaccine design and formulation to address different diseases, including the recent outbreak of SARS-CoV-2. Special emphasis of this review is on the technical and practical aspects of vaccine construction and theranostic approaches to precisely target and localize the active compounds.

Long-Term Protection Elicited by a DNA Vaccine Candidate Expressing the prM-E Antigen of Dengue Virus Serotype 3 in Mice

Dengue virus (DENV) is the causative agent of dengue, and its incidence has increased 30-fold in the past five decades. Among the four cocirculating serotypes, DENV3 is associated with an increased number of severe infections and has become widespread. Vaccination is the mainstay of prevention in reducing disease burden. Previously, the protective efficacy of DNA vaccine candidates toward DENV1, 2, and 4 was confirmed in mice. In this study, a DNA vaccine candidate (pVAX1-D3ME) expressing the prM and E proteins of DENV3 was constructed, and then the immunogenicity and protection were assessed in mice to further develop a tetravalent dengue vaccine. Moreover, the cross-reactive immune responses against the other three serotypes were investigated. The results showed that three doses of 50 μg of pVAX1-D3ME were sufficient to induce strong antigen-specific T cell responses and robust and consistent neutralizing antibodies. Additionally, immunization with pVAX1-D3ME offered protective immunity against not only DENV3 but also the other three serotypes, which could be observed even after 12 months. This study shows great promise for the further evaluation of a dengue tetravalent DNA vaccine candidate in large animal models, including non-human primates.

BVDV Npro protein mediates the BVDV induced immunosuppression through interaction with cellular S100A9 protein

The innate immune response is a vital part of the body's antiviral defense system. The innate immune response is initiated by various receptor interactions, including danger associated molecular patterns (DAMPs). The S100A9 is a member of the DAMPs protein family and, is released by activated phagocytic cells such as neutrophils, monocytes, macrophages or endothelial cells, and S100A9 induces its effect through TLR4/MyD88 pathway.

Bovine viral diarrhea virus (BVDV) is one of the major devastating disease in the cattle industry worldwide. It shows its effect through immunosuppression and develops persistent infection in calves born from infected cows. The current study revealed that BVDV potentially induced immunosuppression by the interaction of BVDV Npro protein with cellular S100A9 protein. The Inhibition of S100A9 protein expression by small interfering RNA (siRNA) enhanced the virus replication in infected cells. Overexpression of bovine S100A9 enhanced the ncpBVDV2a 1373 mediated Type-I interferon production. A co-immunoprecipitation experiment demonstrated a strong interaction between ncp BVDV2a 1373 Npro protein and cellular S100A9 protein. This suggested that BVDV Npro reduced the S100A9 protein availability/activity in infected cells, resulting in reduced Type-I interferon production. A further study of S100A9-BVDV interaction will be need for better understanding of BVDV pathophysiology.

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The bovine viral diarrhea virus (BVDV) nonstructural protein, Npro, is responsible for immunosuppression.

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The mechanism of Npro immune immunosuppression is not well characterized.

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S100A9, a cell protein that contains danger associated molecular patterns (DAMP), is important in innate immunity.

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S100A9 protein and Npro protein associate while overexpression of S100A9 enhanced Type-I interferon production.

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Inhibition of S100A9 by siRNA aided BVDV replication. Npro interacting with S100A9 may result in immunosuppression.

Zika virus-like particle (VLP) based vaccine

The newly emerged mosquito-borne Zika virus poses a major public challenge due to its ability to cause significant birth defects and neurological disorders. The impact of sexual transmission is unclear but raises further concerns about virus dissemination. No specific treatment or vaccine is currently available, thus the development of a safe and effective vaccine is paramount. Here we describe a novel strategy to assemble Zika virus-like particles (VLPs) by co-expressing the structural (CprME) and non-structural (NS2B/NS3) proteins, and demonstrate their effectiveness as vaccines. VLPs are produced in a suspension culture of mammalian cells and self-assembled into particles closely resembling Zika viruses as shown by electron microscopy studies. We tested various VLP vaccines and compared them to analogous compositions of an inactivated Zika virus (In-ZIKV) used as a reference. VLP immunizations elicited high titers of antibodies, as did the In-ZIKV controls. However, in mice the VLP vaccine stimulated significantly higher virus neutralizing antibody titers than comparable formulations of the In-ZIKV vaccine. The serum neutralizing activity elicited by the VLP vaccine was enhanced using a higher VLP dose and with the addition of an adjuvant, reaching neutralizing titers greater than those detected in the serum of a patient who recovered from a Zika infection in Brazil in 2015. Discrepancies in neutralization levels between the VLP vaccine and the In-ZIKV suggest that chemical inactivation has deleterious effects on neutralizing epitopes within the E protein. This along with the inability of a VLP vaccine to cause infection makes it a preferable candidate for vaccine development.

Pre-clinical development of a hydrogen peroxide-inactivated West Nile virus vaccine

West Nile virus (WNV) is a mosquito-transmitted pathogen with a wide geographical range that can lead to long-term disability and death in some cases. Despite the public health risk posed by WNV, including an estimated 3 million infections in the United States alone, no vaccine is available for use in humans. Here, we present a scaled manufacturing approach for production of a hydrogen peroxide-inactivated whole virion WNV vaccine, termed HydroVax-001WNV. Vaccination resulted in robust virus-specific neutralizing antibody responses and protection against WNV-associated mortality in mice or viremia in rhesus macaques (RM). A GLP-compliant toxicology study performed in rats demonstrated an excellent safety profile with clinical findings limited to minor and transient irritation at the injection site. An in vitro relative potency (IVRP) assay was developed and shown to correlate with in vivo responses following forced degradation studies. Long-term in vivo potency comparisons between the intended storage condition (2-8°C) and a thermally stressed condition (40±2°C) demonstrated no loss in vaccine efficacy or protective immunity over a 6-month span of time. Together, the positive pre-clinical findings regarding immunogenicity, safety, and stability indicate that HydroVax-001WNV is a promising vaccine candidate.

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.

Trials and Tribulations on the Path to Developing a Dengue Vaccine

Dengue is a rapidly expanding global health problem. Development of a safe and efficacious tetravalent vaccine along with strategic application of vector control activities represents a promising approach to reducing the global disease burden. Although many vaccine development challenges exist, numerous candidates are in clinical development and one has been tested in three clinical endpoint studies. The results of these studies have raised numerous questions about how we measure vaccine immunogenicity and how these readouts are associated with clinical outcomes in vaccine recipients who experience natural infection. In this review the authors discuss the dengue vaccine pipeline, development challenges, the dengue vaccine-immunologic profiling intersection, and research gaps.

Formaldehyde crosslinking: a tool for the study of chromatin complexes

Formaldehyde has been used for decades to probe macromolecular structure and function and to trap complexes, cells, and tissues for further analysis. Formaldehyde crosslinking is routinely employed for detection and quantification of protein-DNA interactions, interactions between chromatin proteins, and interactions between distal segments of the chromatin fiber. Despite widespread use and a rich biochemical literature, important aspects of formaldehyde behavior in cells have not been well described. Here, we highlight features of formaldehyde chemistry relevant to its use in analyses of chromatin complexes, focusing on how its properties may influence studies of chromatin structure and function.

Safety and Immunogenicity of a Dengue Virus Serotype-1 Purified-Inactivated Vaccine: Results of a Phase 1 Clinical Trial

We describe the results from a human clinical trial of a dengue virus serotype-1, purified-inactivated vaccine (DENV-1 PIV) adjuvanted with aluminum hydroxide. This first-in-man, Phase 1, open-label clinical trial consisted of two groups of flavivirus-naïve healthy adult volunteers that received two intramuscular vaccine doses of either 2.5 μg or 5 μg of DENV-1 PIV administered on days 0 and 28. Following vaccination, both vaccine doses exhibited an acceptable safety profile with minimal injection site and systemic reactions. By study day 42, 2 weeks following the second vaccine dose, all volunteers in both vaccine groups developed serum-neutralizing antibodies against DENV-1. Additional testing using an enzyme-linked immunosorbent assay demonstrated induction of a humoral immune response following both vaccine doses. The DENV-1 PIV was safe and immunogenic in a small number of volunteers supporting development and further testing of a tetravalent DENV PIV formulation.

Developing a dengue vaccine: progress and future challenges

Dengue is an expanding public health problem in the tropics and subtropical areas. Millions of people, most from resource-constrained countries, seek treatment every year for dengue-related disease. Despite more than 70 years of effort, a safe and efficacious vaccine remains unavailable. Antidengue antiviral drugs also do not exist despite attempts to develop or repurpose drug compounds. Gaps in the knowledge of dengue immunology, absence of a validated animal or human model of disease, and suboptimal assay platforms to measure immune responses following infection or experimental vaccination are obstacles to drug and vaccine development efforts. The limited success of one vaccine candidate in a recent clinical endpoint efficacy trial challenges commonly held beliefs regarding potential correlates of protection. If a dengue vaccine is to become a reality in the near term, vaccine developers should expand development pathway explorations beyond those typically required to demonstrate safety and efficacy.

Development of a new hydrogen peroxide–based vaccine platform

Safe and effective vaccines are crucial for maintaining public health and reducing the global burden of infectious disease. Here we introduce a new vaccine platform that uses hydrogen peroxide (H(2)O(2)) to inactivate viruses for vaccine production. H(2)O(2) rapidly inactivates both RNA and DNA viruses with minimal damage to antigenic structure or immunogenicity and is a highly effective method when compared with conventional vaccine inactivation approaches such as formaldehyde or β-propiolactone. Mice immunized with H(2)O(2)-inactivated lymphocytic choriomeningitis virus (LCMV) generated cytolytic, multifunctional virus-specific CD8(+) T cells that conferred protection against chronic LCMV infection. Likewise, mice vaccinated with H(2)O(2)-inactivated vaccinia virus or H(2)O(2)-inactivated West Nile virus showed high virus-specific neutralizing antibody titers and were fully protected against lethal challenge. Together, these studies demonstrate that H(2)O(2)-based vaccines are highly immunogenic, provide protection against a range of viral pathogens in mice and represent a promising new approach to future vaccine development.

Bioinformatics in new generation flavivirus vaccines

Flavivirus infections are the most prevalent arthropod-borne infections world wide, often causing severe disease especially among children, the elderly, and the immunocompromised. In the absence of effective antiviral treatment, prevention through vaccination would greatly reduce morbidity and mortality associated with flavivirus infections. Despite the success of the empirically developed vaccines against yellow fever virus, Japanese encephalitis virus and tick-borne encephalitis virus, there is an increasing need for a more rational design and development of safe and effective vaccines. Several bioinformatic tools are available to support such rational vaccine design. In doing so, several parameters have to be taken into account, such as safety for the target population, overall immunogenicity of the candidate vaccine, and efficacy and longevity of the immune responses triggered. Examples of how bio-informatics is applied to assist in the rational design and improvements of vaccines, particularly flavivirus vaccines, are presented and discussed.

Role of amphotericin B upon enhancement of protective immunity elicited by oral administration with liposome-encapsulated-Japanese encephalitis virus nonstructural protein 1 (NS1) in mice

Amphotericin B (AmB) is an antifungal antibiotic the activity of which has been associated with modulation of pro-inflammatory cytokines expression in cultured cells. Herein we reveal that co-administration with AmB enhances the immunogenicity of oral Lip-JENS1 vaccine which derived from liposomes functionalized with DSPC (distearoylphosphatidylcholine) and cholesterol (2:1, molar ratio)-bearing JE virus NS1 protein (600 microg ml(-1)). Oral single dose of Lip-JENS1 elicited a detectable serum NS1-specific IgG antibody response from a mouse model. Remarkably, the addition of AmB (125 microg per mouse), particularly, 2 h prior to, but not simultaneously with, the administration of Lip-JENS1 significantly enhanced the systemic antigen-specific antibody response, providing superior protection against lethal JEV challenges. Further, we observed AmB-induced the transcription of cytokine expression and translocation of transcriptional factor NF-kappaB from the cytoplasm to the nucleus for the murine macrophage J774A.1. Moreover, Peyer's-patch lymphocytes (PPL) from AmB-treated mice produced high levels of IL-1beta, IL-6 and TNF-alpha expression compared to the corresponding control of cells from non-treated mice. Taken together, the results suggest that AmB exerts a profound influence upon mucosal vaccination with Lip-JENS1, possibly playing an adjuvant-augmented role to "fine-tune" humoral as well as cellular immune response, thus conferring enhanced protective immunity for immunising individuals against JE infection.

Recent approaches in hantavirus vaccine development

Rodent-borne hantaviruses are associated with two main clinical disorders in humans: hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome. Although hantavirus diseases can be life threatening and numerous research efforts are focused on the development of hantavirus prevention, no specific antiviral therapy is yet available and, at this time, no WHO-approved vaccine has gained widespread acceptance. This review will summarize the current knowledge and recent progress as well as new speculative approaches in the development of hantavirus vaccines.

Utility of formaldehyde cross-linking and mass spectrometry in the study of protein-protein interactions

For decades, formaldehyde has been routinely used to cross-link proteins in cells, tissue, and in some instances, even entire organisms. Due to its small size, formaldehyde can readily permeate cell walls and membranes, resulting in efficient cross-linking, i.e. the formation of covalent bonds between proteins, DNA, and other reactive molecules. Indeed, formaldehyde cross-linking is an instrumental component of many mainstream analytical/cell biology techniques including chromatin immunoprecipitation (ChIP) of protein-DNA complexes found in nuclei; immunohistological analysis of protein expression and localization within cells, tissues, and organs; and mass spectrometry (MS)-compatible silver-staining methodologies used to visualize low abundance proteins in polyacrylamide gels. However, despite its exquisite suitability for use in the analysis of protein environments within cells, formaldehyde has yet to be commonly employed in the directed analysis of protein-protein interactions and cellular networks. The general purpose of this article is to discuss recent advancements in the use of formaldehyde cross-linking in combination with MS-based methodologies. Key advantages and limitations to the use of formaldehyde over other cross-linkers and technologies currently used to study protein-protein interactions are highlighted, and formaldehyde-based experimental approaches that are proving very promising in their ability to accurately and efficiently identify novel protein-protein and multiprotein interaction complexes are presented.

An immunogenic and protective alphavirus replicon particle-based dengue vaccine overcomes maternal antibody interference in weanling mice

A candidate pediatric dengue virus (DENV) vaccine based on nonpropagating Venezuelan equine encephalitis virus replicon particles (VRP) was tested for immunogenicity and protective efficacy in weanling mice in the presence and absence of potentially interfering maternal antibodies. A gene cassette encoding envelope proteins prM and E from mouse-adapted DENV type 2 (DENV2) strain NGC was cloned into a VEE replicon vector and packaged into VRP, which programmed proper in vitro expression and processing of DENV2 envelope proteins upon infection of Vero cells. Primary immunization of 3-week-old weanling BALB/c mice in the footpad with DENV2 VRP resulted in high levels of DENV-specific serum immunoglobulin G antibodies and significant titers of neutralizing antibodies in all vaccinates. A booster immunization 12 weeks after the prime immunization resulted in increased neutralizing antibodies that were sustained for at least 30 weeks. Immunization at a range of doses of DENV2 VRP protected mice from an otherwise-lethal intracranial DENV2 challenge. To model vaccination in the presence of maternal antibodies, weanling pups born to DENV2-immune or DENV2-naïve dams were immunized with either DENV2 VRP or live DENV2 given peripherally. The DENV2 VRP vaccine induced neutralizing-antibody responses in young mice regardless of the maternal immune status. In contrast, live-DENV2 vaccination performed poorly in the presence of preexisting anti-DENV2 antibodies. This study demonstrates the feasibility of a VRP vaccine approach as an early-life DENV vaccine in populations with high levels of circulating DENV antibodies and suggests the utility of VRP-based vaccines in other instances where maternal antibodies make early vaccination problematic.

Efficacy of a live attenuated tetravalent candidate dengue vaccine in naïve and previously infected cynomolgus macaques

The development of a safe and effective vaccine against dengue is a public health priority. Attempts to evaluate candidate vaccine formulations in human volunteers were largely unsuccessful, at least in part due to too high reactogenicity of some of the candidate vaccines tested. We evaluated a live attenuated tetravalent dengue vaccine candidate in flavivirus naïve and dengue virus type 3 immune non-human primates. Immune responses were measured both at the humoral and the cellular level and the efficacy of this vaccine candidate was evaluated by challenging the vaccinated animals with dengue virus type 4. Humoral and cellular immune responses upon vaccination were similar to those described after natural infection in humans. All animals were protected from developing viremia upon challenge infection. In addition, primary dengue virus type 3 infection of macaques neither influenced the immune response upon vaccination, nor interfered with vaccine-induced protection from dengue virus type 4 challenge infection. The data suggest that the live attenuated tetravalent vaccine candidate used is promising and warrant further safety and efficacy testing in clinical trials.

Bacterially expressed and refolded envelope protein (domain III) of dengue virus type-4 binds heparan sulfate

An arboviral infection like dengue fever/dengue hemorrhagic fever (DHF) with high morbidity and mortality rate are extensively prevalent in several parts of the world. Global efforts have been directed towards development of vaccine for prevention of dengue. However, lack of thorough understanding about biology and pathogenesis of dengue virus restricts us from development of an effective vaccine. Here we report molecular interaction of domain III of envelope protein of dengue virus type-4 with heparan sulfate. A codon optimized synthetic gene encoding domain III of dengue virus type-4 envelope protein was expressed in Escherichia coli and purified under denaturing conditions, refolded and purified to homogeneity. Refolded Den4-DIII was characterized using biochemical and biophysical methods and shown to be pure and homogeneous. The purified protein was recognized in Western analyses by monoclonal antibody specific for the 6x His tag as well as the H241 monoclonal antibody. The in vitro refolded recombinant protein preparation was biologically functional and found to bind cell free heparan sulfate. This is the first report providing molecular evidence on binding of dengue-4 envelope protein to heparan sulfate. We developed a homology model of dengue-4 envelope protein (domain III) and mapped the possible amino acid residues critical for binding to heparan sulfate. Domain III envelope protein of dengue virus is a lead vaccine candidate. Our findings further the understanding on biology of dengue virus and will help in development of bioassay for the proposed vaccine candidate.

An inactivated West Nile virus vaccine for domestic geese-efficacy study and a summary of 4 years of field application

Following the isolation in 1997 of West Nile virus from the brains of geese with an acute neuroparalytic disease in Israel, which reappeared in the following years, an inactivated vaccine was prepared from suckling mouse brains. The brain homogenate was inactivated with formaldehyde and blended with mineral oil adjuvant. In 2000, the first flocks were vaccinated according to a schedule of two subcutaneous doses, commencing at the age of 2 weeks and given with a 2-weeks interval. In efficacy trials, the challenge virus was injected at 7 weeks by the intracranial route, and over 85% protection was recorded in vaccinated geese. In extensive field trials conducted in 2001--2003, the vaccine was demonstrated to be safe and efficacious, and over 3 million doses were manufactured in 2000--2003.

New developments in flavivirus vaccines with special attention to yellow fever

PURPOSE OF REVIEW

Here we review recent epidemiological trends in flavivirus diseases, findings related to existing vaccines, and new directions in flavivirus vaccine research. We emphasize the need for stepped-up efforts to stop further spread and intensification of these infections worldwide.

RECENT FINDINGS

Although the incidence and geographic distribution of flavivirus diseases have increased in recent years, human vaccines are available only for yellow fever, Japanese encephalitis, tick-borne encephalitis and Kyasanur forest disease. Factors contributing to resurgence include insufficient supplies of available vaccines, incomplete vaccination coverage and relaxation in vector control. Research has been underway for 60 years to develop effective vaccines against dengue, and recent progress is encouraging. The development of vaccines against West Nile, virus recently introduced to North America, has been initiated. In addition, there is considerable interest in improving existing vaccines with respect to increasing safety (e.g. eliminating the newly recognized syndrome of yellow fever vaccine-associated viscerotropic adverse disease), and to reducing the cost and number of doses required for effective immunization.

SUMMARY

Traditional approaches to flavivirus vaccines are still employed, while recent advancements in biotechnology produced new approaches to vaccine design, such as recombinant live virus, subunit and DNA vaccines. Live chimeric vaccines against dengue, Japanese encephalitis and West Nile based on yellow fever 17D virus (ChimeriVax) are in phase I/II trials, with encouraging results. Other chimeric dengue, tick-borne encephalitis and West Nile virus candidates were developed based on attenuated dengue backbones. To further reduce the impact of flavivirus diseases, vaccination policies and vector control programs in affected countries require revision.

Immunogenicity and protective efficacy in mice of a formaldehyde-inactivated Indian strain of Japanese encephalitis virus grown in Vero cells

P20778, an Indian strain of Japanese encephalitis virus (JEV) obtained from Vellore in the Southern India, was grown in Vero cells cultured on microcarriers in a spinner flask. The virus was formalin-inactivated and its immunogenicity and protective efficacy in mice were tested in comparison with a commercially available vaccine. Our studies indicated that formalin-inactivated JEV P20778 induced high levels of protective immunity in mice. Virus inactivation with formalin at 22 degrees C, which required shorter incubation period, was found to be as good or better to virus inactivation at 4 degrees C for generating high titers of anti-JEV antibodies. Similarly, the 22 degrees C-inactivated virus generated JEV neutralizing antibody titers as good or higher than those induced by the 4 degrees C-inactivated virus. Thus, for the vaccine production, inactivation of JEV with formalin at 22 degrees C would be a preferred method as it is faster and does not require cold room storage.

An attenuated West Nile prototype virus is highly immunogenic and protects against the deadly NY99 strain: a candidate for live WN vaccine development

In a short time, West Nile virus has developed into a nationwide health and veterinary problem. The high virulence of the circulating virus and related lineage 1 WN strains hinders development of an attenuated live vaccine. We describe an attenuated WN isolate, WN1415, which is a molecularly cloned descendant of the WN prototype B956 strain. The parent virus belongs to lineage 2, members of which have not been associated with epidemic or epizootic outbreaks. A set of non-conservative mutations, mostly in non-structural protein genes, distinguishes the WN1415 isolate from the parent B956 prototype strain. Immunization with WN1415 (55-550,000 pfu) established a potent immunity, which protected the majority of mice against lethal challenge with WN NY99. The attenuated nature of the isolate and its excellent growth characteristics combined with the availability of a highly stable infectious clone make the isolate an attractive candidate for live WN vaccine development.

Recent advancement in flavivirus vaccine development

Lately, the magnitude of cumulative diseases burden caused by flaviviruses, such as dengue virus, Japanese encephalitis virus, tick-borne encephalitis virus, West Nile virus and yellow fever virus, has reached an unprecedented level with the sizes of human and animal populations at risk increasing sharply. These diseases present highly complex medical, economic and ecologic problems, some effecting primarily human and others affecting human, livestock and wildlife. The large body of recent publications on the development of vaccines taking advantage of new generations of bio-engineering techniques clearly reflects the profound interests and deep sense of urgency in the scientific and medical communities in combating those diseases. This review reveals a collection of remarkable progresses thus far made in flaviviral vaccine research not only employing a diverse range of new strategies but also re-tooling old techniques to improve the existing vaccines. The efficacy and safety of some of the new vaccine candidates have been evaluated and proven in human clinical trials. Besides the technical advancement in vaccine development, in this review, the importance of somewhat neglected and yet critical subjects, such as adequacy of animal model, vaccine safety, vaccine formulation and delivery, complication in serodiagostics and economic factor, was examined in-depth.