Chikungunya Vaccine Candidates: Current Landscape and Future Prospects

Pathogenicity and virulence of chikungunya virus

Chikungunya virus (CHIKV) is a mosquito-transmitted, RNA virus that causes an often-severe musculoskeletal illness characterized by fever, joint pain, and a range of debilitating symptoms. The virus has re-emerged as a global health threat in recent decades, spreading from its origin in Africa across Asia and the Americas, leading to widespread outbreaks impacting millions of people. Despite more than 50 years of research into the pathogenesis of CHIKV, there is still no curative treatment available. Current management of CHIKV infections primarily involves providing supportive care to alleviate symptoms and improve the patient's quality of life. Given the ongoing threat of CHIKV, there is an urgent need to better understand its pathogenesis. This understanding is crucial for deciphering the mechanisms underlying the disease and for developing effective strategies for both prevention and management. This review aims to provide a comprehensive overview of CHIKV and its pathogenesis, shedding light on the complex interactions of viral genetics, host factors, immune responses, and vector-related factors. By exploring these intricate connections, the review seeks to contribute to the knowledge base surrounding CHIKV, offering insights that may ultimately lead to more effective prevention and management strategies for this re-emerging global health threat.

Chikungunya Virus Vaccines: A Review of IXCHIQ and PXVX0317 from Pre-Clinical Evaluation to Licensure

Chikungunya virus is an emerging mosquito-borne alphavirus that causes febrile illness and arthritic disease. Chikungunya virus is endemic in 110 countries and the World Health Organization estimates that it has caused more than 2 million cases of crippling acute and chronic arthritis globally since it re-emerged in 2005. Chikungunya virus outbreaks have occurred in Africa, Asia, Indian Ocean islands, South Pacific islands, Europe, and the Americas. Until recently, no specific countermeasures to prevent or treat chikungunya disease were available. To address this need, multiple vaccines are in human trials. These vaccines use messenger RNA-lipid nanoparticles, inactivated virus, and viral vector approaches, with a live-attenuated vaccine VLA1553 and a virus-like particle PXVX0317 in phase III testing. In November 2023, the US Food and Drug Administration (FDA) approved the VLA1553 live-attenuated vaccine, which is marketed as IXCHIQ. In June 2024, Health Canada approved IXCHIQ, and in July 2024, IXCHIQ was approved by the European Commission. On August 13, 2024, the US FDA granted priority review for PXVX0317. The European Medicine Agency is considering accelerated assessment review of PXVX0317, with potential for approval by both agencies in 2025. In this review, we summarize published data from pre-clinical and clinical trials for the IXCHIQ and PXVX0317 vaccines. We also discuss unanswered questions including potential impacts of pre-existing chikungunya virus immunity on vaccine safety and immunogenicity, whether long-term immunity can be achieved, safety in children, pregnant, and immunocompromised individuals, and vaccine efficacy in people with previous exposure to other emerging alphaviruses in addition to chikungunya virus.

Immunogenicity and Safety of Chikungunya Vaccines: A Systematic Review and Meta-Analysis

Several vaccines against chikungunya fever have been developed and tested, and one has been recently licensed. We performed a meta-analysis to estimate the immunogenicity and safety of all chikungunya vaccines that have been progressed to clinical trial evaluation (VLA1553; mRNA-1388/VAL-181388; PXVX0317/VRC-CHKVLP059-00-VP; ChAdOx1 Chik; MV-CHIK). We included trials retrieved from MedLine, Scopus, and ClinicalTrials.gov. The outcomes were the rates of seroconversion/seroresponse and serious adverse events (SAEs) after the primary immunization course. We retrieved a total of 14 datasets, including >4000 participants. All candidate chikungunya vaccines were able to elicit an immunogenic response in ≥96% of vaccinated subjects, regardless of the vaccination schedule and platform used, and the seroconversion/seroresponse rates remained high 6 to 12 months after vaccination for most vaccines. Four of the five candidate vaccines showed a good overall safety profile (no data were available for ChAdOx1 Chik), with no significant increase in the risk of SAEs among the vaccinated, and a low absolute risk of product-related SAEs. Overall, the present findings support the potential use of the candidate vaccines for the prevention of chikungunya and the current indication for use in adult travelers to endemic regions of the licensed VLA 1553 vaccine. In order to extend chikungunya vaccination to a wider audience, further studies are needed on individuals from endemic countries and frail populations.

Live-attenuated CHIKV vaccine with rearranged genome replicates in vitro and induces immune response in mice

Chikungunya fever virus (CHIKV) is a mosquito-borne alphavirus that causes wide-spread human infections and epidemics in Asia, Africa and recently, in the Americas. CHIKV is considered a priority pathogen by CEPI and WHO. Despite recent approval of a live-attenuated CHIKV vaccine, development of additional vaccines is warranted due to the worldwide outbreaks of CHIKV. Previously, we developed immunization DNA (iDNA) plasmid capable of launching live-attenuated CHIKV vaccine in vivo. Here we report the use of CHIKV iDNA plasmid to prepare a novel, live-attenuated CHIKV vaccine V5040 with rearranged RNA genome. In V5040, genomic RNA was rearranged to encode capsid gene downstream from the glycoprotein genes. Attenuated mutations derived from experimental CHIKV 181/25 vaccine were also engineered into E2 gene of V5040. The DNA copy of rearranged CHIKV genomic RNA with attenuated mutations was cloned into iDNA plasmid pMG5040 downstream from the CMV promoter. After transfection in vitro, pMG5040 launched replication of V5040 virus with rearranged genome and attenuating E2 mutations. Furthermore, V5040 virus was evaluated in experimental murine models for general safety and immunogenicity. Vaccination with V5040 virus subcutaneously resulted in elicitation of CHIKV-specific, virus-neutralizing antibodies. The results warrant further evaluation of V5040 virus with rearranged genome as a novel live-attenuated vaccine for CHIKV.

Development of Vaccines against Emerging Mosquito-Vectored Arbovirus Infections

Among emergent climate-sensitive infectious diseases, some mosquito-vectored arbovirus infections have epidemiological, social, and economic effects. Dengue virus (DENV), West Nile virus (WNV), and Chikungunya virus (CHIKV) disease, previously common only in the tropics, currently pose a major risk to global health and are expected to expand dramatically in the near future if adequate containment measures are not implemented. The lack of safe and effective vaccines is critical as it seems likely that emerging mosquito-vectored arbovirus infections will be con-trolled only when effective and safe vaccines against each of these infections become available. This paper discusses the clinical characteristics of DENV, WNV, and CHIKV infections and the state of development of vaccines against these viruses. An ideal vaccine should be able to evoke with a single administration a prompt activation of B and T cells, adequate concentrations of protecting/neutralizing antibodies, and the creation of a strong immune memory capable of triggering an effective secondary antibody response after new infection with a wild-type and/or mutated infectious agent. Moreover, the vaccine should be well tolerated, safe, easily administrated, cost-effective, and widely available throughout the world. However, the development of vaccines against emerging mosquito-vectored arbovirus diseases is far from being satisfactory, and it seems likely that it will take many years before effective and safe vaccines for all these infections are made available worldwide.

Maxizyme-mediated suppression of chikungunya virus replication and transmission in transgenic Aedes aegypti mosquitoes

Chikungunya virus (CHIKV) is an emerging mosquito-borne pathogen of significant public health importance. There are currently no prophylactic vaccines or therapeutics available to control CHIKV. One approach to arbovirus control that has been proposed is the replacement of transmission-competent mosquitoes with those that are refractory to virus infection. Several transgene effectors are being examined as potentially useful for this population replacement approach. We previously demonstrated the successful use of hammerhead ribozymes (hRzs) as an antiviral effector transgene to control CHIKV infection of, and transmission by, Aedes mosquitoes. In this report we examine a maxizyme approach to enhance the catalytic activity and prevent virus mutants from escaping these ribozymes. We designed a maxizyme containing minimized (monomer) versions of two hRzs we previously demonstrated to be the most effective in CHIKV suppression. Three versions of CHIKV maxizyme were designed: Active (Mz), inactive (ΔMz), and a connected CHIKV maxizyme (cMz). The maxizymes with their expression units (Ae-tRNA val promoter and its termination signal) were incorporated into lentivirus vectors with selection and visualization markers. Following transformation, selection, and single-cell sorting of Vero cells, clonal cell populations were infected with CHIKV at 0.05 and 0.5 MOI, and virus suppression was assessed using TCID50-IFA, RT-qPCR, and caspase-3 assays. Five transgenic mosquito lines expressing cMz were generated and transgene insertion sites were confirmed by splinkerette PCR. Our results demonstrate that Vero cell clones expressing Mz exhibited complete inhibition of CHIKV replication compared to their respective inactive control version or the two parent hRzs. Upon oral challenge of transgenic mosquitoes with CHIKV, three out of the five lines were completely refractory to CHIKV infection, and all five lines tested negative for salivary transmission. Altogether, this study demonstrates that maxizymes can provide a higher catalytic activity and viral suppression than hRzs.

A measles virus-based vaccine induces robust chikungunya virus-specific CD4+ T-cell responses in a phase II clinical trial

Chikungunya virus (CHIKV) is an alphavirus transmitted by mosquitos that causes a debilitating disease characterized by fever and long-lasting polyarthralgia. To date, no vaccine has been licensed, but multiple vaccine candidates are under evaluation in clinical trials. One of these vaccines is based on a measles virus vector encoding for the CHIKV structural genes C, E3, E2, 6K, and E1 (MV-CHIK), which proved safe in phase I and II clinical trials and elicited CHIKV-specific antibody responses in adult measles seropositive vaccine recipients. Here, we predicted T-cell epitopes in the CHIKV structural genes and investigated whether MV-CHIK vaccination induced CHIKV-specific CD4+ and/or CD8+ T-cell responses. Immune-dominant regions containing multiple epitopes in silico predicted to bind to HLA class II molecules were found for four of the five structural proteins, while no such regions were predicted for HLA class I. Experimentally, CHIKV-specific CD4+ T-cells were detected in six out of twelve participants after a single MV-CHIK vaccination and more robust responses were found 4 weeks after two vaccinations (ten out of twelve participants). T-cells were mainly directed against the three large structural proteins C, E2 and E1. Next, we sorted and expanded CHIKV-specific T cell clones (TCC) and identified human CHIKV T-cell epitopes by deconvolution. Interestingly, eight out of nine CD4+ TCC recognized an epitope in accordance with the in silico prediction. CHIKV-specific CD8+ T-cells induced by MV-CHIK vaccination were inconsistently detected. Our data show that the MV-CHIK vector vaccine induced a functional transgene-specific CD4+ T cell response which, together with the evidence of neutralizing antibodies as correlate of protection for CHIKV, makes MV-CHIK a promising vaccine candidate in the prevention of chikungunya.

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.

Live-Attenuated CHIKV Vaccine with Rearranged Genome Replicates in vitro and Induces Immune Response in Mice

Chikungunya fever virus (CHIKV) is a mosquito-borne alphavirus that causes wide-spread human infections and epidemics in Asia, Africa and recently, in the Americas. There is no approved vaccine and CHIKV is considered a priority pathogen by CEPI and WHO. Previously, we developed immunization DNA (iDNA) plasmid capable of launching live-attenuated CHIKV vaccine in vivo . Here we report the use of CHIKV iDNA plasmid to prepare a novel, live-attenuated CHIKV vaccine V5040 with rearranged RNA genome for improved safety. In V5040, genomic RNA was rearranged to encode capsid gene downstream from the glycoprotein genes. To secure safety profile, attenuated mutations derived from experimental CHIKV 181/25 vaccine were also engineered into E2 gene of V5040. The DNA copy of rearranged CHIKV genomic RNA with attenuated mutations was cloned into iDNA plasmid pMG5040 downstream from the CMV promoter. After transfection in vitro, pMG5040 launched replication of V5040 virus with rearranged genome and attenuating E2 mutations. Furthermore, V5040 virus was evaluated in experimental murine models for safety and immunogenicity. Vaccination with V5040 virus subcutaneously resulted in elicitation of CHIKV-specific, virus-neutralizing antibodies. The results warrant further evaluation of V5040 virus with rearranged genome as a novel live-attenuated vaccine for CHIKV.

Strategic considerations on developing a CHIKV vaccine and ensuring equitable access for countries in need

Chikungunya is an arboviral disease caused by the chikungunya virus (CHIKV) afflicting tropical and sub-tropical countries worldwide. It has been identified as a priority pathogen by the Coalition for Epidemics Preparedness Innovations (CEPI) and as an emerging infectious disease (EID) necessitating further action as soon as possible by the World Health Organization (WHO). Recent studies suggest that disability-adjusted life years (DALYs) due to CHIKV infection are as high as 106,089 DALYs lost globally. Significant progress has been made in the development of several vaccines, aimed at preventing CHIKV infections. This perspective article summarizes CEPI's efforts and strategic considerations for developing a CHIKV vaccine and ensuring equitable access for CHIKV endemic countries.

Heterologous DNA Prime- Subunit Protein Boost with Chikungunya Virus E2 Induces Neutralizing Antibodies and Cellular-Mediated Immunity

Chikungunya virus (CHIKV) has become a significant public health concern due to the increasing number of outbreaks worldwide and the associated comorbidities. Despite substantial efforts, there is no specific treatment or licensed vaccine against CHIKV to date. The E2 glycoprotein of CHIKV is a promising vaccine candidate as it is a major target of neutralizing antibodies during infection. In this study, we evaluated the immunogenicity of two DNA vaccines (a non-targeted and a dendritic cell-targeted vaccine) encoding a consensus sequence of E2_CHIKV and a recombinant protein (E2*_CHIKV). Mice were immunized with different homologous and heterologous DNAprime-E2* protein boost strategies, and the specific humoral and cellular immune responses were accessed. We found that mice immunized with heterologous non-targeted DNA prime- E2*_CHIKV protein boost developed high levels of neutralizing antibodies, as well as specific IFN-γ producing cells and polyfunctional CD4⁺ and CD8⁺ T cells. We also identified 14 potential epitopes along the E2_CHIKV protein. Furthermore, immunization with recombinant E2*_CHIKV combined with the adjuvant AS03 presented the highest humoral response with neutralizing capacity. Finally, we show that the heterologous prime-boost strategy with the non-targeted pVAX-E2 DNA vaccine as the prime followed by E2* protein + AS03 boost is a promising combination to elicit a broad humoral and cellular immune response. Together, our data highlights the importance of E2_CHIKV for the development of a CHIKV vaccine.

An Overview of Indian Biomedical Research on the Chikungunya Virus with Particular Reference to Its Vaccine, an Unmet Medical Need

Chikungunya virus (CHIKV) is an infectious agent spread by mosquitos, that has engendered endemic or epidemic outbreaks of Chikungunya fever (CHIKF) in Africa, South-East Asia, America, and a few European countries. Like most tropical infections, CHIKV is frequently misdiagnosed, underreported, and underestimated; it primarily affects areas with limited resources, like developing nations. Due to its high transmission rate and lack of a preventive vaccine or effective treatments, this virus poses a serious threat to humanity. After a 32-year hiatus, CHIKV reemerged as the most significant epidemic ever reported, in India in 2006. Since then, CHIKV-related research was begun in India, and up to now, more than 800 peer-reviewed research papers have been published by Indian researchers and medical practitioners. This review gives an overview of the outbreak history and CHIKV-related research in India, to favor novel high-quality research works intending to promote effective treatment and preventive strategies, including vaccine development, against CHIKV infection.

In silico design and validation of a novel multi-epitope vaccine candidate against structural proteins of Chikungunya virus using comprehensive immunoinformatics analyses

Chikungunya virus (CHIKV) is an emerging viral infectious agent with the potential of causing pandemic. There is neither a protective vaccine nor an approved drug against the virus. The aim of this study was design of a novel multi-epitope vaccine (MEV) candidate against the CHIKV structural proteins using comprehensive immunoinformatics and immune simulation analyses. In this study, using comprehensive immunoinformatics approaches, we developed a novel MEV candidate using the CHIKV structural proteins (E1, E2, 6 K, and E3). The polyprotein sequence was obtained from the UniProt Knowledgebase and saved in FASTA format. The helper and cytotoxic T lymphocytes (HTLs and CTLs respectively) and B cell epitopes were predicted. The toll-like receptor 4 (TLR4) agonist RS09 and PADRE epitope were employed as promising immunostimulatory adjuvant proteins. All vaccine components were fused using proper linkers. The MEV construct was checked in terms of antigenicity, allergenicity, immunogenicity, and physicochemical features. The docking of the MEV construct and the TLR4 and molecular dynamics (MD) simulation were also performed to assess the binding stability. The designed construct was non-allergen and was immunogen which efficiently stimulated immune responses using the proper synthetic adjuvant. The MEV candidate exhibited acceptable physicochemical features. Immune provocation included prediction of HTL, B cell, and CTL epitopes. The docking and MD simulation confirmed the stability of the docked TLR4-MEV complex. The high-level protein expression in the Escherichia coli (E. coli) host was observed through in silico cloning. The in vitro, in vivo, and clinical trial investigations are required to verify the findings of the current study.