Development of Zika Virus Vaccines

Mitigating the effects of climate change on human health with vaccines and vaccinations

Climate change represents an unprecedented threat to humanity and will be the ultimate challenge of the 21st century. As a public health consequence, the World Health Organization estimates an additional 250,000 deaths annually by 2030, with resource-poor countries being predominantly affected. Although climate change's direct and indirect consequences on human health are manifold and far from fully explored, a growing body of evidence demonstrates its potential to exacerbate the frequency and spread of transmissible infectious diseases. Effective, high-impact mitigation measures are critical in combating this global crisis. While vaccines and vaccination are among the most cost-effective public health interventions, they have yet to be established as a major strategy in climate change-related health effect mitigation. In this narrative review, we synthesize the available evidence on the effect of climate change on vaccine-preventable diseases. This review examines the direct effect of climate change on water-related diseases such as cholera and other enteropathogens, helminthic infections and leptospirosis. It also explores the effects of rising temperatures on vector-borne diseases like dengue, chikungunya, and malaria, as well as the impact of temperature and humidity on airborne diseases like influenza and respiratory syncytial virus infection. Recent advances in global vaccine development facilitate the use of vaccines and vaccination as a mitigation strategy in the agenda against climate change consequences. A focused evaluation of vaccine research and development, funding, and distribution related to climate change is required.

Global Dynamics of a Reaction-Diffusion Model of Zika Virus Transmission with Seasonality

In this paper, we propose a periodic reaction-diffusion model of Zika virus with seasonal and spatial heterogeneous structure in host and vector population. We introduce the basic reproduction ratio [Formula: see text] for this model and show that the disease-free periodic solution is globally asymptotically stable if [Formula: see text], while the system admits a globally asymptotically stable positive periodic solution if [Formula: see text]. Numerically, we study the Zika transmission in Rio de Janeiro Municipality, Brazil, and investigate the effects of some model parameters on [Formula: see text]. We find that the neglect of seasonality underestimates the value of [Formula: see text] and the maximum carrying capacity affects the spread of Zika virus.

Recent advances in immunotherapies against infectious diseases

Immunotherapies are disease management strategies that target or manipulate components of the immune system. Infectious diseases pose a significant threat to human health as evidenced by countries continuing to grapple with several emerging and re-emerging diseases, the most recent global health threat being the SARS-CoV2 pandemic. As such, various immunotherapeutic approaches are increasingly being investigated as alternative therapies for infectious diseases, resulting in significant advances towards the uncovering of pathogen-host immunity interactions. Novel and innovative therapeutic strategies are necessary to overcome the challenges typically faced by existing infectious disease prevention and control methods such as lack of adequate efficacy, drug toxicity, and the emergence of drug resistance. As evidenced by recent developments and success of pharmaceuticals such as monoclonal antibodies (mAbs), immunotherapies already show abundant promise to overcome such limitations while also advancing the frontiers of medicine. In this review, we summarize some of the most notable inroads made to combat infectious disease, over mainly the last 5 years, through the use of immunotherapies such as vaccines, mAb-based therapies, T-cell-based therapies, manipulation of cytokine levels, and checkpoint inhibition. While its most general applications are founded in cancer treatment, advances made towards the curative treatment of human immunodeficiency virus, tuberculosis, malaria, zika virus and, most recently COVID-19, reinforce the role of immunotherapeutic strategies in the broader field of disease control. Ultimately, the comprehensive specificity, safety, and cost of immunotherapeutics will impact its widespread implementation.

Vector-borne diseases in pregnancy

Vector-borne infections cause a significant proportion of world-wide morbidity and mortality and many are increasing in incidence. This is due to a combination of factors, primarily environmental change, encroachment of human habitats from urban to peri-urban areas and rural to previously uninhabited areas, persistence of poverty, malnutrition and resource limitation in geographical areas where these diseases are endemic. Pregnant women represent the single largest ‘at risk’ group, due to immune-modulation and a unique physiological state. Many of these diseases have not benefitted from the same level of drug development as other infectious and medical domains, a factor attributing to the ‘neglected tropical disease’ title many vector-borne diseases hold. Pregnancy compounds this issue as data for safety and efficacy for many drugs is practically non-existent, precluding exposure in pregnancy to many first-line therapeutic agents for ‘fear of the unknown’ or overstated adverse pregnancy-foetal outcomes. In this review, major vector-borne diseases, their impact on pregnancy outcomes, current treatment, vaccination and short-comings of current medical practice for pregnant women will be discussed.

Computational tools for modern vaccine development

Vaccines play an essential role in controlling the rates of fatality and morbidity. Vaccines not only arrest the beginning of different diseases but also assign a gateway for its elimination and reduce toxicity. This review gives an overview of the possible uses of computational tools for vaccine design. Moreover, we have described the initiatives of utilizing the diverse computational resources by exploring the immunological databases for developing epitope-based vaccines, peptide-based drugs, and other resources of immunotherapeutics. Finally, the applications of multi-graft and multivalent scaffolding, codon optimization and antibodyomics tools in identifying and designing in silico vaccine candidates are described.

Serological evidence of DENV, JEV, and ZIKV among the indigenous people (Orang Asli) of Peninsular Malaysia

Dengue virus (DENV), Japanese encephalitis virus (JEV), and Zika virus (ZIKV) are mosquito-borne flavivirus of medical importance in tropical countries such as Malaysia. However, much remains unknown regarding their prevalence among the underserved indigenous people (Orang Asli) living in communities in the forest fringe areas of Peninsular Malaysia. Information on the prevalence of diseases is necessary to elevate the effectiveness of disease control and preventive measures. This study aimed to determine the seroprevalence of the three major flaviviruses among the Orang Asli and investigate the association between demographic factors and seropositivities. Sampling activities were conducted in the Orang Asli villages to obtain serum samples and demographic data from consenting volunteers. The presence of DENV, JEV, and ZIKV immunoglobulin G (IgG) antibodies in the sera were examined using commercial enzyme-linked immunosorbent assay kits. A focus reduction neutralization assay was performed to measure virus-specific neutralizing antibodies. A total of 872 serum samples were obtained from the Orang Asli volunteers. Serological assay results revealed that DENV IgG, JEV IgG, and ZIKV IgG seropositivities among the Orang Asli were at 4.9%, 48.4%, and 13.2%, respectively. Neutralizing antibodies (FRNT50 ≥ 1:40) against JEV and ZIKV were found in 86.7% and 100.0%, respectively, out of the samples tested. Positive serology to all three viruses corresponded significantly to the age of the volunteers with increasing seropositivity in older volunteers. Findings from the study suggest that Orang Asli are at significant risk of contracting JEV and ZIKV infections despite the lack of active transmission of the viruses in the country.

Zika Virus-Derived E-DIII Protein Displayed on Immunologically Optimized VLPs Induces Neutralizing Antibodies without Causing Enhancement of Dengue Virus Infection

Zika virus (ZIKV) is a flavivirus similar to Dengue virus (DENV) in terms of transmission and clinical manifestations, and usually both viruses are found to co-circulate. ZIKV is usually transmitted by mosquitoes bites, but may also be transmitted by blood transfusion, via the maternal–foetal route, and sexually. After 2015, when the most extensive outbreak of ZIKV had occurred in Brazil and subsequently spread throughout the rest of South America, it became evident that ZIKV infection during the first trimester of pregnancy was associated with microcephaly and other neurological complications in newborns. As a result, the development of a vaccine against ZIKV became an urgent goal. A major issue with DENV vaccines, and therefore likely also with ZIKV vaccines, is the induction of antibodies that fail to neutralize the virus properly and cause antibody-dependent enhancement (ADE) of the infection instead. It has previously been shown that antibodies against the third domain of the envelope protein (EDIII) induces optimally neutralizing antibodies with no evidence for ADE for other viral strains. Therefore, we generated a ZIKV vaccine based on the EDIII domain displayed on the immunologically optimized Cucumber mosaic virus (CuMVtt) derived virus-like particles (VLPs) formulated in dioleoyl phosphatidylserine (DOPS) as adjuvant. The vaccine induced high levels of specific IgG after a single injection. The antibodies were able to neutralise ZIKV without enhancing infection by DENV in vitro. Thus, the here described vaccine based on EDIII displayed on VLPs was able to stimulate production of antibodies specifically neutralizing ZIKV without potentially enhancing disease caused by DENV.

Identification of relevant regions on structural and nonstructural proteins of Zika virus for vaccine and diagnostic test development: an in silico approach

Zika virus (ZIKV) is an arbovirus belonging to the Flaviviridae family and the genus Flavivirus. Infection with ZIKV causes a mild, self-limiting febrile illness called Zika fever. However, ZIKV infection has been recently associated with microcephaly and Guillain-Barré syndrome. Vaccines for the disease are a high priority of World Health Organization. Several studies are currently being conducted to develop a vaccine against ZIKV, but until now there is no licensed ZIKV vaccine. This study used a novel immunoinformatics approach to identify potential T-cell immunogenic epitopes present in the structural and nonstructural proteins of ZIKV. Fourteen T-cell candidate epitopes were identified on ZIKV structural and nonstructural proteins: pr^36-50; C^61-75; C^103-117; E^374-382; E^477-491; NS2a^90-104; NS2a^174-188; NS2a^179-193; NS2a^190-204; NS2a^195-209; NS2a^200-214; NS3^175-189; and NS4a^82-96; NS4a^99-113. Among these epitopes, only E^374-382 is a human leukocyte antigen (HLA) type I restricted epitope. All identified epitopes showed a low similarity with other important flaviviruses but had a high conservation rate among the ZIKV strains and a high population coverage rate. Therefore, these predicted T-cell epitopes are potential candidates targets for development of vaccines to prevent ZIKV infection.

Human T cell leukemia virus type 1 and Zika virus: tale of two reemerging viruses with neuropathological sequelae of public health concern

Human T cell leukemia virus type 1 (HTLV-1) and Zika virus (ZIKV) have been considered neglected viruses of low public health concern until recently when incidences of HTLV-1 and ZIKV were observed to be linked to serious immune-related disease and neurological complications. This review will discuss the epidemiology, genomic evolution, virus-host interactions, virulence factors, neuropathological sequelae, and current perspectives of these reemerging viruses. There are no FDA-approved therapeutics or vaccines against these viruses, and as such, it is important for clinical trials to focus on developing vaccines that can induce cell-mediated immune response to confer long-term protective immunity. Furthermore, attention should be paid to reducing the transmission of these viruses through unprotected sex, infected blood during sharing of contaminated needles, donated blood and organs, and vertical transmission from mother to baby via breastfeeding. There is an urgent need to re-evaluate repurposing current antiviral therapies as well as developing novel antiviral agents with enhanced efficacy due to the high morbidity rate associated with these two reemerging chronic viral diseases.

A Vaccine Based on a Modified Vaccinia Virus Ankara Vector Expressing Zika Virus Structural Proteins Controls Zika Virus Replication in Mice

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus that affects humans and can cause severe neurological complications, including Guillain-Barré syndrome and microcephaly. Since 2007 there have been three large outbreaks; the last and larger spread in the Americas in 2015. Actually, ZIKV is circulating in the Americas, Southeast Asia, and the Pacific Islands, and represents a potential pandemic threat. Given the rapid ZIKV dissemination and the severe neurological and teratogenic sequelae associated with ZIKV infection, the development of a safe and efficacious vaccine is critical. In this study, we have developed and characterized the immunogenicity and efficacy of a novel ZIKV vaccine based on the highly attenuated poxvirus vector modified vaccinia virus Ankara (MVA) expressing the ZIKV prM and E structural genes (termed MVA-ZIKV). MVA-ZIKV expressed efficiently the ZIKV structural proteins, assembled in virus-like particles (VLPs) and was genetically stable upon nine passages in cell culture. Immunization of mice with MVA-ZIKV elicited antibodies that were able to neutralize ZIKV and induced potent and polyfunctional ZIKV-specific CD8⁺ T cell responses that were mainly of an effector memory phenotype. Moreover, a single dose of MVA-ZIKV reduced significantly the viremia in susceptible immunocompromised mice challenged with live ZIKV. These findings support the use of MVA-ZIKV as a potential vaccine against ZIKV.

Zika Virus Vaccines: Challenges and Perspectives

Zika virus is an arbovirus that has rapidly spread within the Americas since 2014, presenting a variety of clinical manifestations and neurological complications resulting in congenital malformation, microcephaly, and possibly, in male infertility. These significant clinical manifestations have led investigators to develop several candidate vaccines specific to Zika virus. In this review we describe relevant targets for the development of vaccines specific for Zika virus, the development status of various vaccine candidates and their different platforms, as well as their clinical progression.

Zika virus vaccines: immune response, current status, and future challenges

Zika virus (ZIKV) is the most recent mosquito-transmitted virus to cause a global health crisis following its entrance into a naïve population in the Western Hemisphere. Once the ZIKV outbreak began investigators rapidly established small and large animal models of pathogenesis, developed a number candidate vaccines using different platforms, and defined mechanisms of protection. In this review, we characterize the adaptive immune response elicited by ZIKV infections and vaccines, the status of ongoing clinical trials in humans, and discuss future challenges within the field.

A mathematical model for Zika virus transmission dynamics with a time-dependent mosquito biting rate

BACKGROUND

Mathematical modeling has become a tool used to address many emerging diseases. One of the most basic and popular modeling frameworks is the compartmental model. Unfortunately, most of the available compartmental models developed for Zika virus (ZIKV) transmission were designed to describe and reconstruct only past, short-time ZIKV outbreaks in which the effects of seasonal change to entomological parameters can be ignored. To make an accurate long-term prediction of ZIKV transmission, the inclusion of seasonal effects into an epidemic model is unavoidable.

METHODS

We developed a vector-borne compartmental model to analyze the spread of the ZIKV during the 2015-2016 outbreaks in Bahia, Brazil and to investigate the impact of two vector control strategies, namely, reducing mosquito biting rates and reducing mosquito population size. The model considered the influences of seasonal change on the ZIKV transmission dynamics via the time-varying mosquito biting rate. The model was also validated by comparing the model prediction with reported data that were not used to calibrate the model.

RESULTS

We found that the model can give a very good fit between the simulation results and the reported Zika cases in Bahia (R-square = 0.9989). At the end of 2016, the total number of ZIKV infected people was predicted to be 1.2087 million. The model also predicted that there would not be a large outbreak from May 2016 to December 2016 due to the decrease of the susceptible pool. Implementing disease mitigation by reducing the mosquito biting rates was found to be more effective than reducing the mosquito population size. Finally, the correlation between the time series of estimated mosquito biting rates and the average temperature was also suggested.

CONCLUSIONS

The proposed ZIKV transmission model together with the estimated weekly biting rates can reconstruct the past long-time multi-peak ZIKV outbreaks in Bahia.

Zika virus, vaccines, and antiviral strategies

INTRODUCTION

Zika virus (ZIKV) recently emerged as a global public health emergency of international concern. ZIKV is responsible for severe neurological complications in adults and infection during pregnancy and can lead to congenital Zika syndrome. There is no licensed vaccine or drug to prevent or treat ZIKV infection. Areas covered: The aim of this article is to provide an overview and update of the progress of research on anti-ZIKV vaccine and medications until the end of 2017, with a special emphasis on drugs that can be used during pregnancy. Expert commentary: Development of new vaccines and drugs is challenging and several points particular to ZIKV infections augment this difficulty: (1) Cross-reactions between ZIKV and other flaviviruses, the impact of ZIKV vaccination on subsequent flavivirus infections, and vice-versa, is unknown, (2) Drugs against ZIKV should be safe in pregnant women, and (3) Evaluation of the efficacy of vaccine and drugs against ZIKV in clinical trials phase II-IV will be complicated due to the decline of ZIKV circulation.