Recent Progress in Vaccine Development Against Chikungunya Virus

Antiviral evaluation of 1,4-disubstituted-1,2,3-triazole derivatives against Chikungunya virus

Aim

This work aimed to investigate the antiviral activity of two 1,4-disubstituted-1,2,3-triazole derivatives (1 and 2) against Chikungunya virus (CHIKV) replication.

Materials & methods

Cytotoxicity was analyzed using colorimetric assays and the antiviral potential was evaluated using plaque assays and computational tools.

Results

Compound 2 showed antiviral activity against CHIKV 181-25 in BHK-21 and Vero cells. Also, this compound presented a higher activity against CHIKV BRA/RJ/18 in Vero cells, like compound 1. Compound 2 exhibited virucidal activity and inhibited virus entry while compound 1 inhibited virus release. Molecular docking suggested that these derivatives inhibit nsP1 protein while compound 1 may also target capsid protein.

Conclusion

Both compounds exhibit promising antiviral activity against CHIKV by blocking different steps of virus replication.

Host Factor Nucleophosmin 1 (NPM1/B23) Exerts Antiviral Effects against Chikungunya Virus by Its Interaction with Viral Nonstructural Protein 3

Chikungunya virus (CHIKV) hijacks host cell machinery to support its replication. Nucleophosmin 1 (NPM1/B23), a nucleolar phosphoprotein, is one of the host proteins known to restrict CHIKV infection; however, the mechanistic details of the antiviral role of NPM1 are not elucidated. It was seen in our experiments that the level of NPM1 expression affected the expression levels of interferon-stimulated genes (ISGs) that play antiviral roles in CHIKV infection, such as IRF1, IRF7, OAS3, and IFIT1, indicating that one of the antiviral mechanisms could be through modulation of interferon-mediated pathways. Our experiments also identified that for CHIKV restriction, NPM1 must move from the nucleus to the cytoplasm. A deletion of the nuclear export signal (NES), which confines NPM1 within the nucleus, abolishes its anti-CHIKV action. We observed that NPM1 binds CHIKV nonstructural protein 3 (nsP3) strongly via its macrodomain, thereby exerting a direct interaction with viral proteins to limit infection. Based on site-directed mutagenesis and coimmunoprecipitation studies, it was also observed that amino acid residues N24 and Y114 of the CHIKV nsP3 macrodomain, known to be involved in virus virulence, bind ADP-ribosylated NPM1 to inhibit infection. Overall, the results show a key role of NPM1 in CHIKV restriction and indicate it as a promising host target for developing antiviral strategies against CHIKV. IMPORTANCE Chikungunya, a recently reemerged mosquito-borne infection caused by a positive-sense, single-stranded RNA virus, has caused explosive epidemics in tropical regions. Unlike the classical symptoms of acute fever and debilitating arthralgia, incidences of neurological complications and mortality were reported. Currently there are no antivirals or commercial vaccines available against chikungunya. Like all viruses, CHIKV uses host cellular machinery for establishment of infection and successful replication. To counter this, the host cell activates several restriction factors and innate immune response mediators. Understanding these host-virus interactions helps to develop host-targeted antivirals against the disease. Here, we report the antiviral role of the multifunctional host protein NPM1 against CHIKV. The significant inhibitory effect of this protein against CHIKV involves its increased expression and movement from its natural location within the nucleus to the cytoplasm. There, it interacts with functional domains of key viral proteins. Our results support ongoing efforts toward development of host-directed antivirals against CHIKV and other alphaviruses.

Advances in mRNA vaccines for viral diseases

Since the onset of the pandemic caused by severe acute respiratory syndrome coronavirus 2, messenger RNA (mRNA) vaccines have demonstrated outstanding performance. mRNA vaccines offer significant advantages over conventional vaccines in production speed and cost-effectiveness, making them an attractive option against other viral diseases. This article reviewed recent advances in viral mRNA vaccines and their delivery systems to provide references and guidance for developing mRNA vaccines for new viral diseases.

A phase 1, randomized, placebo-controlled, dose-ranging study to evaluate the safety and immunogenicity of an mRNA-based chikungunya virus vaccine in healthy adults

BACKGROUND

Chikungunya, a mosquito-borne viral disease caused by the chikungunya virus (CHIKV), causes a significant global health burden, and there is currently no approved vaccine to prevent chikungunya disease. In this study, the safety and immunogenicity of a CHIKV mRNA vaccine candidate (mRNA-1388) were evaluated in healthy participants in a CHIKV-nonendemic region.

METHODS

This phase 1, first-in-human, randomized, placebo-controlled, dose-ranging study enrolled healthy adults (ages 18-49 years) between July 2017 and March 2019 in the United States. Participants were randomly assigned (3:1) to receive 2 intramuscular injections 28 days apart with mRNA-1388 in 3 dose-level groups (25 μg, 50 μg, and 100 μg) or placebo and were followed for up to 1 year. Safety (unsolicited adverse events [AEs]), tolerability (local and systemic reactogenicity; solicited AEs), and immunogenicity (geometric mean titers [GMTs] of CHIKV neutralizing and binding antibodies) of mRNA-1388 versus placebo were evaluated.

RESULTS

Sixty participants were randomized and received ≥ 1 vaccination; 54 (90 %) completed the study. mRNA-1388 demonstrated favorable safety and reactogenicity profiles at all dose levels. Immunization with mRNA-1388 induced substantial and persistent humoral responses. Dose-dependent increases in neutralizing antibody titers were observed; GMTs (95 % confidence intervals [CIs]) at 28 days after dose 2 were 6.2 (5.1-7.6) for mRNA-1388 25 μg, 53.8 (26.8-108.1) for mRNA-1388 50 μg, 92.8 (43.6-197.6) for mRNA-1388 100 μg, and 5.0 (not estimable) for placebo. Persistent humoral responses were observed up to 1 year after vaccination and remained higher than placebo in the 2 higher mRNA-1388 dose groups. The development of CHIKV-binding antibodies followed a similar trend as that observed with neutralizing antibodies.

CONCLUSIONS

mRNA-1388, the first mRNA vaccine against CHIKV, was well tolerated and elicited substantial and long-lasting neutralizing antibody responses in healthy adult participants in a nonendemic region.

CLINICALTRIALS

gov: NCT03325075.

Application of Traditional Vaccine Development Strategies to SARS-CoV-2

Over the past 150 years, vaccines have revolutionized the relationship between people and disease. During the COVID-19 pandemic, technologies such as mRNA vaccines have received attention due to their novelty and successes. However, more traditional vaccine development platforms have also yielded important tools in the worldwide fight against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A variety of approaches have been used to develop COVID-19 vaccines that are now authorized for use in countries around the world. In this review, we highlight strategies that focus on the viral capsid and outwards, rather than on the nucleic acids inside. These approaches fall into two broad categories: whole-virus vaccines and subunit vaccines. Whole-virus vaccines use the virus itself, in either an inactivated or an attenuated state. Subunit vaccines contain instead an isolated, immunogenic component of the virus. Here, we highlight vaccine candidates that apply these approaches against SARS-CoV-2 in different ways. In a companion article (H. M. Rando, R. Lordan, L. Kolla, E. Sell, et al., mSystems 8:e00928-22, 2023, https://doi.org/10.1128/mSystems.00928-22), we review the more recent and novel development of nucleic acid-based vaccine technologies. We further consider the role that these COVID-19 vaccine development programs have played in prophylaxis at the global scale. Well-established vaccine technologies have proved especially important to making vaccines accessible in low- and middle-income countries. Vaccine development programs that use established platforms have been undertaken in a much wider range of countries than those using nucleic acid-based technologies, which have been led by wealthy Western countries. Therefore, these vaccine platforms, though less novel from a biotechnological standpoint, have proven to be extremely important to the management of SARS-CoV-2. IMPORTANCE The development, production, and distribution of vaccines is imperative to saving lives, preventing illness, and reducing the economic and social burdens caused by the COVID-19 pandemic. Vaccines that use cutting-edge biotechnology have played an important role in mitigating the effects of SARS-CoV-2. However, more traditional methods of vaccine development that were refined throughout the 20th century have been especially critical to increasing vaccine access worldwide. Effective deployment is necessary to reducing the susceptibility of the world's population, which is especially important in light of emerging variants. In this review, we discuss the safety, immunogenicity, and distribution of vaccines developed using established technologies. In a separate review, we describe the vaccines developed using nucleic acid-based vaccine platforms. From the current literature, it is clear that the well-established vaccine technologies are also highly effective against SARS-CoV-2 and are being used to address the challenges of COVID-19 globally, including in low- and middle-income countries. This worldwide approach is critical for reducing the devastating impact of SARS-CoV-2.

Application of Traditional Vaccine Development Strategies to SARS-CoV-2

Over the past 150 years, vaccines have revolutionized the relationship between people and disease. During the COVID-19 pandemic, technologies such as mRNA vaccines have received attention due to their novelty and successes. However, more traditional vaccine development platforms have also yielded important tools in the worldwide fight against the SARS-CoV-2 virus. A variety of approaches have been used to develop COVID-19 vaccines that are now authorized for use in countries around the world. In this review, we highlight strategies that focus on the viral capsid and outwards, rather than on the nucleic acids inside. These approaches fall into two broad categories: whole-virus vaccines and subunit vaccines. Whole-virus vaccines use the virus itself, either in an inactivated or attenuated state. Subunit vaccines contain instead an isolated, immunogenic component of the virus. Here, we highlight vaccine candidates that apply these approaches against SARS-CoV-2 in different ways. In a companion manuscript, we review the more recent and novel development of nucleic-acid based vaccine technologies. We further consider the role that these COVID-19 vaccine development programs have played in prophylaxis at the global scale. Well-established vaccine technologies have proved especially important to making vaccines accessible in low- and middle-income countries. Vaccine development programs that use established platforms have been undertaken in a much wider range of countries than those using nucleic-acid-based technologies, which have been led by wealthy Western countries. Therefore, these vaccine platforms, though less novel from a biotechnological standpoint, have proven to be extremely important to the management of SARS-CoV-2.

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.

Long lasting anti-IgG chikungunya seropositivity in the Mayotte population will not be enough to prevent future outbreaks: A seroprevalence study, 2019

Chikungunya is an arboviral disease causing arthralgia which may develop into a debilitating chronic arthritis. In Mayotte, a French overseas department in the Indian Ocean, a chikungunya outbreak was reported in 2006, affecting a third of the population. We aimed at assessing the chikungunya seroprevalence in this population, after over a decade from that epidemic. A multi-stage cross sectional household-based study exploring socio-demographic factors, and knowledge and attitude towards mosquito-borne disease prevention was carried out in 2019. Blood samples from participants aged 15-69 years were taken for chikungunya IgG serological testing. We analyzed associations between chikungunya serological status and selected factors using Poisson regression models, and estimated weighted and adjusted prevalence ratios (w/a PR). The weighted seroprevalence of chikungunya was 34.75% (n = 2853). Seropositivity for IgG anti-chikungunya virus was found associated with living in Mamoudzou (w/a PR = 1.49, 95%CI: 1.21-1.83) and North (w/a PR = 1.41, 95%CI: 1.08-1.84) sectors, being born in the Comoros islands (w/a PR = 1.30, 95%CI: 1.03-1.61), being a student or unpaid trainee (w/a PR = 1.35, 95%CI: 1.01-1.81), living in precarious housing (w/a PR = 1.30, 95%CI: 1.02-1.67), accessing water streams for bathing (w/a PR = 1.72, 95%CI: 1.1-2.7) and knowing that malaria is a mosquito-borne disease (w/a PR = 1.42, 95%CI: 1.21-1.83). Seropositivity was found inversely associated with high education level (w/a PR = 0.50, 95%CI: 0.29-0.86) and living in households with access to running water and toilets (w/a PR = 0.64, 95%CI: 0.51-0.80) (n = 1438). Our results indicate a long-lasting immunity from chikungunya exposure. However, the current population seroprevalence is not enough to protect from future outbreaks. Individuals naïve to chikungunya and living in precarious socio-economic conditions are likely to be at high risk of infection in future outbreaks. To prevent and prepare for future chikungunya epidemics, it is essential to address socio-economic inequalities as a priority, and to strengthen chikungunya surveillance in Mayotte.

Understanding the Biology and Immune Pathogenesis of Chikungunya Virus Infection for Diagnostic and Vaccine Development

Chikungunya virus, the causative agent of chikungunya fever, is generally characterized by the sudden onset of symptoms, including fever, rash, myalgia, and headache. In some patients, acute chikungunya virus infection progresses to severe and chronic arthralgia that persists for years. Chikungunya infection is more commonly identified in tropical and subtropical regions. However, recent expansions and epidemics in the temperate regions have raised concerns about the future public health impact of chikungunya diseases. Several underlying factors have likely contributed to the recent re-emergence of chikungunya infection, including urbanization, human travel, viral adaptation to mosquito vectors, lack of effective control measures, and the spread of mosquito vectors to new regions. However, the true burden of chikungunya disease is most likely to be underestimated, particularly in developing countries, due to the lack of standard diagnostic assays and clinical manifestations overlapping with those of other endemic viral infections in the regions. Additionally, there have been no chikungunya vaccines available to prevent the infection. Thus, it is important to update our understanding of the immunopathogenesis of chikungunya infection, its clinical manifestations, the diagnosis, and the development of chikungunya vaccines.

mRNA Vaccine Designing Using Chikungunya Virus E Glycoprotein through Immunoinformatics-Guided Approaches

Chikungunya virus is an alphavirus transmitted by mosquitos that develops into chikungunya fever and joint pain in humans. This virus’ name originated from a Makonde term used to describe an illness that changes the joints and refers to the posture of afflicted patients who are affected by excruciating joint pain. There is currently no commercially available drug or vaccine for chikungunya virus infection and the treatment is performed by symptom reduction. Herein, we have developed a computationally constructed mRNA vaccine construct featuring envelope glycoprotein as the target molecule to aid in the treatment process. We have utilized the reverse vaccinology approach to determine epitopes that would generate adaptive immune reactions. The resulting T and B lymphocytes epitopes were screened by various immunoinformatic tools and a peptide vaccine construct was designed. It was validated by proceeding to docking and MD simulation studies. The following design was then back-translated in nucleotide sequence and codons were optimized according to the expression host system (H. sapiens). Various sequences, including 3′ and 5′ UTR regions, Kozak sequence, poly (A) tail, etc., were introduced into the sequence for the construction of the final mRNA vaccine construct. The secondary structure was generated for validation of the mRNA vaccine construct sequence. Additionally, in silico cloning was also performed to design a vector for proceeding towards in vitro experimentation. The proposed designed vaccine construct may proceed with experimental testing for further efficacy verification and the final development of a vaccine against chikungunya virus infection.

Vaccines against Emerging and Neglected Infectious Diseases: An Overview

Neglected Tropical Diseases (NTDs) are a group of diseases that are highly prevalent in tropical and subtropical regions, and closely associated with poverty and marginalized populations. Infectious diseases affect over 1.6 billion people annually, and vaccines are the best prophylactic tool against them. Along with NTDs, emerging and reemerging infectious diseases also threaten global public health, as they can unpredictably result in pandemics. The recent advances in vaccinology allowed the development and licensing of new vaccine platforms that can target and prevent these diseases. In this work, we discuss the advances in vaccinology and some of the difficulties found in the vaccine development pipeline for selected NTDs and emerging and reemerging infectious diseases, including HIV, Dengue, Ebola, Chagas disease, malaria, leishmaniasis, zika, and chikungunya.

Visualization of conformational changes and membrane remodeling leading to genome delivery by viral class-II fusion machinery

Chikungunya virus (CHIKV) is a human pathogen that delivers its genome to the host cell cytoplasm through endocytic low pH-activated membrane fusion mediated by class-II fusion proteins. Though structures of prefusion, icosahedral CHIKV are available, structural characterization of virion interaction with membranes has been limited. Here, we have used cryo-electron tomography to visualize CHIKV's complete membrane fusion pathway, identifying key intermediary glycoprotein conformations coupled to membrane remodeling events. Using sub-tomogram averaging, we elucidate features of the low pH-exposed virion, nucleocapsid and full-length E1-glycoprotein's post-fusion structure. Contrary to class-I fusion systems, CHIKV achieves membrane apposition by protrusion of extended E1-glycoprotein homotrimers into the target membrane. The fusion process also features a large hemifusion diaphragm that transitions to a wide pore for intact nucleocapsid delivery. Our analyses provide comprehensive ultrastructural insights into the class-II virus fusion system function and direct mechanistic characterization of the fundamental process of protein-mediated membrane fusion.

Effectiveness of CHIKV vaccine VLA1553 demonstrated by passive transfer of human sera

Chikungunya virus (CHIKV) is a reemerging mosquito-borne alphavirus responsible for numerous outbreaks. Chikungunya can cause debilitating acute and chronic disease. Thus, the development of a safe and effective CHIKV vaccine is an urgent global health priority. This study evaluated the effectiveness of the live-attenuated CHIKV vaccine VLA1553 against WT CHIKV infection by using passive transfer of sera from vaccinated volunteers to nonhuman primates (NHP) subsequently exposed to WT CHIKV and established a serological surrogate of protection. We demonstrated that human VLA1553 sera transferred to NHPs conferred complete protection from CHIKV viremia and fever after challenge with homologous WT CHIKV. In addition, serum transfer protected animals from other CHIKV-associated clinical symptoms and from CHIKV persistence in tissue. Based on this passive transfer study, a 50% micro–plaque reduction neutralization test titer of ≥ 150 was determined as a surrogate of protection, which was supported by analysis of samples from a seroepidemiological study. In conclusion, considering the unfeasibility of an efficacy trial due to the unpredictability and explosive, rapidly moving nature of chikungunya outbreaks, the definition of a surrogate of protection for VLA1553 is an important step toward vaccine licensure to reduce the medical burden caused by chikungunya.

Novel molecular approaches to combat vectors and vector-borne viruses: Special focus on RNA interference (RNAi) mechanisms

Vector-borne diseases, such as dengue, chikungunya, zika, yellow fever etc pose significant burden among the infectious diseases globally, especially in tropical and sub-tropical regions. Globalization, deforestation, urbanization, climate change, uncontrolled population growth, inadequate waste management and poor vector-management infrastructure have all contributed to the expansion of vector habitats and subsequent increase in vector-borne diseases throughout the world. Conventional vector control methods, such as use of insecticides, have significant negative environmental repercussions in addition to developing resistance in vectors. Till date, a very few vaccines or antiviral therapies have been approved for the treatment of vector borne diseases. In this review, we have discussed emerging molecular approaches like CRISPR (clustered regularly interspaced short palindromic repeats)/Cas-9, sterile insect technique (SIT), release of insects carrying a dominant lethal (RIDL), Wolbachia (virus transmission blocking) and RNA interference (RNAi) to combat vector and vector-borne viruses. Due to the extensive advancements in RNAi research, a special focus has been given on its types, biogenesis, mechanism of action, delivery and experimental studies evaluating their application as anti-mosquito and anti-viral agent. These technologies appear to be highly promising in terms of contributing to vector control and antiviral drug development, and hence can be used to reduce global vector and vector-borne disease burden.

Two Conserved Phenylalanine Residues in the E1 Fusion Loop of Alphaviruses Are Essential for Viral Infectivity

Alphaviruses infect cells by a low pH-dependent fusion reaction between viral and host cell membranes that is mediated by the viral E1 glycoprotein. Most reported alphavirus E1 sequences include two phenylalanines (F87 and F95) in the fusion loop, yet the role of these residues in viral infectivity remains to be defined. Following introduction of wild type (WT), E1-F87A, and E1-F95A chikungunya virus (CHIKV) RNA genomes into cells, viral particle production was similar in magnitude. However, CHIKV E1-F87A and E1-F95A virions displayed impaired infectivity compared with WT CHIKV particles. Although WT, E1-F87A, and E1-F95A particles bound cells with similar efficiencies, E1-F87A and E1-F95A particles were unable to undergo fusion and entry into cells. Introduction of an F95A mutation in the E1 fusion loop of Mayaro virus or Venezuelan equine encephalitis virus also resulted in poorly infectious virions. We further tested whether an E1-F87A or E1-F95A mutation could be incorporated into a live-attenuated vaccine strain, CHIKV 181/25, to enhance vaccine safety. Infection of immunocompromised Ifnar1-/- and Irf3-/-Irf5-/-Irf7-/- mice with 181/25E1-F87A or 181/25E1-F95A resulted in 0% mortality, compared with 100% mortality following 181/25 infection. Despite this enhanced attenuation, surviving Ifnar1-/- and Irf3-/-Irf5-/-Irf7-/- mice were protected against virulent virus re-challenge. Moreover, single-dose immunization of WT mice with either 181/25, 181/25E1-F87A, or 181/25E1-F95A elicited CHIKV-specific antibody responses and protected against pathogenic CHIKV challenge. These studies define a critical function for residues E1-F87 and E1-F95 in alphavirus fusion and entry into target cells and suggest that incorporation of these mutations could enhance the safety of live-attenuated alphavirus vaccine candidates. IMPORTANCE Alphaviruses are human pathogens that cause both debilitating acute and chronic musculoskeletal disease and potentially fatal encephalitis. In this study, we determined that two highly conserved phenylalanine residues in the alphavirus E1 glycoprotein are required for fusion of viral and host cell membranes and viral entry into target cells. We further demonstrated that mutation of these phenylalanines results in a substantial loss of viral virulence but not immunogenicity. These data enhance an understanding of the viral determinants of alphavirus entry into host cells and could contribute to the development of new antivirals targeting these conserved phenylalanines or new live-attenuated alphavirus vaccines.

Expression, Purification, and Refolding of Chikungunya Virus Full-Length Envelope E2 Protein along with B-Cell and T-Cell Epitope Analyses Using Immuno-Informatics Approaches

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus, which causes severe illness in humans and is responsible for epidemic outbreaks in Africa, Asia, North and South America, and Europe. Despite its increased global prevalence, no licensed vaccines are available to date for treating or preventing CHIKV infection. The envelope E2 protein is one of the promising subunit vaccine candidates against CHIKV. In this study, we describe successful cloning, expression, and purification of CHIKV E2 full-length (E2-FL) and truncated (E2-ΔC and E2-ΔNC) proteins in the Escherichia coli expression system. The recombinant E2 proteins were purified from inclusion bodies using Ni-NTA chromatography. Further, we describe a detailed refolding procedure for obtaining the CHIKV E2-FL protein in native conformation, which was confirmed using circular dichroism and Fourier transform infrared spectroscopy. BALB/c mice immunized with the three different E2 proteins exhibited increased E2-specific antibody titers compared to sham-immunized controls, suggesting induction of strong humoral immune response. On analyzing the E2-specific antibody response generated in immunized mice, the CHIKV E2-FL protein was observed to be the most immunogenic among the three different CHIKV E2 antigens used in the study. Our B-cell and T-cell epitope mapping results indicate that the presence of specific immunogenic peptides located in the N-terminal and C-terminal regions of the CHIKV E2-FL protein may contribute to its increased immunogenicity, compared to truncated CHIKV E2 proteins. In summary, our study provides a detailed protocol for expressing, purifying, and refolding of the CHIKV E2-FL protein and provides an understanding of its immunogenic epitopes, which can be exploited for the development of novel multiepitope-based anti-CHIKV vaccine strategies.

Plant-Derived Recombinant Vaccines against Zoonotic Viruses

Emerging and re-emerging zoonotic diseases cause serious illness with billions of cases, and millions of deaths. The most effective way to restrict the spread of zoonotic viruses among humans and animals and prevent disease is vaccination. Recombinant proteins produced in plants offer an alternative approach for the development of safe, effective, inexpensive candidate vaccines. Current strategies are focused on the production of highly immunogenic structural proteins, which mimic the organizations of the native virion but lack the viral genetic material. These include chimeric viral peptides, subunit virus proteins, and virus-like particles (VLPs). The latter, with their ability to self-assemble and thus resemble the form of virus particles, are gaining traction among plant-based candidate vaccines against many infectious diseases. In this review, we summarized the main zoonotic diseases and followed the progress in using plant expression systems for the production of recombinant proteins and VLPs used in the development of plant-based vaccines against zoonotic viruses.

Secreted Trimeric Chikungunya Virus Spikes from Insect Cells: Production, Purification, and Glycosylation Status

Chikungunya virus (CHIKV) is a rapidly emerging mosquito-borne virus that causes a severe febrile illness with long-lasting arthralgia in humans. As there is no vaccine to protect humans and limit CHIKV epidemics, the virus continues to be a global public health concern. The CHIKV envelope glycoproteins E1 and E2 are important immunogens; therefore, the aim of this study is to produce trimeric CHIKV spikes in insect cells using the baculovirus expression system. The CHIKV E1 and E2 ectodomains were covalently coupled by a flexible linker that replaces the 6K transmembrane protein. The C-terminal E1 transmembrane was replaced by a Strep-tag II for the purification of secreted spikes from the culture fluid. After production in Sf9 suspension cells (product yields of 5.8–7.6 mg/L), the CHIKV spikes were purified by Strep-Tactin affinity chromatography, which successfully cleared the co-produced baculoviruses. Bis(sulfosuccinimidyl)suberate cross-linking demonstrated that the spikes are secreted as trimers. PNGase F treatment showed that the spikes are glycosylated. LC–MS/MS-based glycoproteomic analysis confirmed the glycosylation and revealed that the majority are of the mannose- or hybrid-type N-glycans and <2% have complex-type N-glycans. The LC –MS/MS analysis also revealed three O-glycosylation sites in E1. In conclusion, the trimeric, glycosylated CHIKV spikes have been successfully produced in insect cells and are now available for vaccination studies.

Virus-Like Particles: Revolutionary Platforms for Developing Vaccines Against Emerging Infectious Diseases

Virus-like particles (VLPs) are nanostructures that possess diverse applications in therapeutics, immunization, and diagnostics. With the recent advancements in biomedical engineering technologies, commercially available VLP-based vaccines are being extensively used to combat infectious diseases, whereas many more are in different stages of development in clinical studies. Because of their desired characteristics in terms of efficacy, safety, and diversity, VLP-based approaches might become more recurrent in the years to come. However, some production and fabrication challenges must be addressed before VLP-based approaches can be widely used in therapeutics. This review offers insight into the recent VLP-based vaccines development, with an emphasis on their characteristics, expression systems, and potential applicability as ideal candidates to combat emerging virulent pathogens. Finally, the potential of VLP-based vaccine as viable and efficient immunizing agents to induce immunity against virulent infectious agents, including, SARS-CoV-2 and protein nanoparticle-based vaccines has been elaborated. Thus, VLP vaccines may serve as an effective alternative to conventional vaccine strategies in combating emerging infectious diseases.

Tomatidine reduces Chikungunya virus progeny release by controlling viral protein expression

Tomatidine, a natural steroidal alkaloid from unripe green tomatoes has been shown to exhibit many health benefits. We recently provided in vitro evidence that tomatidine reduces the infectivity of Dengue virus (DENV) and Chikungunya virus (CHIKV), two medically important arthropod-borne human infections for which no treatment options are available. We observed a potent antiviral effect with EC50 values of 0.82 μM for DENV-2 and 1.3 μM for CHIKV-LR. In this study, we investigated how tomatidine controls CHIKV infectivity. Using mass spectrometry, we identified that tomatidine induces the expression of p62, CD98, metallothionein and thioredoxin-related transmembrane protein 2 in Huh7 cells. The hits p62 and CD98 were validated, yet subsequent analysis revealed that they are not responsible for the observed antiviral effect. In parallel, we sought to identify at which step of the virus replication cycle tomatidine controls virus infectivity. A strong antiviral effect was seen when in vitro transcribed CHIKV RNA was transfected into Huh7 cells treated with tomatidine, thereby excluding a role for tomatidine during CHIKV cell entry. Subsequent determination of the number of intracellular viral RNA copies and viral protein expression levels during natural infection revealed that tomatidine reduces the RNA copy number and viral protein expression levels in infected cells. Once cells are infected, tomatidine is not able to interfere with active RNA replication yet it can reduce viral protein expression. Collectively, the results delineate that tomatidine controls viral protein expression to exert its antiviral activity. Lastly, sequential passaging of CHIKV in presence of tomatidine did not lead to viral resistance. Collectively, these results further emphasize the potential of tomatidine as an antiviral treatment towards CHIKV infection.

Chikungunya fever is a debilitating disease caused by the mosquito-borne Chikungunya virus. Over the past two decades the geographical spread of the virus and its mosquito vector has drastically increased thereby causing millions of infections. To date there is no antiviral drug and no vaccine available to treat/prevent Chikungunya virus infection. We recently showed that the natural steroidal alkaloid tomatidine has potent antiviral activity towards Chikungunya virus at submicromolar concentrations. In this study we dissected how tomatidine reduces the production of Chikungunya virus particles. We show that tomatidine lowers viral protein expression and we hypothesize that the effect of tomatidine on viral protein translation hampers the production of progeny viral RNA copies / number of infected cells thereby leading to a reduced production of secreted virus particles. Also, we show that Chikungunya virus does not readily become resistant to tomatidine. Collectively, we deciphered the mechanism by which tomatidine exerts antiviral activity to Chikungunya virus and our results strengthen the potential of tomatidine as an antiviral treatment strategy towards Chikungunya virus.

Antibody effector analysis of prime versus prime-boost immunizations with a recombinant measles-vectored chikungunya virus vaccine

Chikungunya is a mosquito-borne disease that causes periodic but explosive epidemics of acute disease throughout the tropical world. Vaccine development against chikungunya virus (CHIKV) has been hampered by an inability to conduct efficacy trials due to the unpredictability of CHIKV outbreaks. Therefore, immune correlates are being explored to gain inference into vaccine-induced protection. This study is an in-depth serological characterization of Fab- and Fc-mediated antibody responses in selected phase II clinical trial participants following immunization with the recombinant measles-vectored CHIKV vaccine, MV-CHIK. Antibody comparisons were conducted between participants who received prime and those who received prime-boost vaccine regimens. MV-CHIK vaccination elicited potent Fab-mediated antibody responses (such as CHIKV-specific IgG, neutralization, and avidity), including dominant IgG3 responses, which translated into strong antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis. At 1 month, prime-boost immunization led to significantly greater responses in every measured Fab and Fc antibody parameter. Interestingly, prime-boost-elicited antibodies decreased rapidly over time, until at 6 months both vaccine regimens displayed similar antibody profiles. Nonetheless, antibody avidity and antibody-dependent cellular phagocytosis remained significantly greater following boost immunization. Our observations suggest that a prime-boost administration of MV-CHIK will be more appropriate for CHIKV-endemic regions, while a prime-only regimen may be sufficient for travel purposes or outbreak situations.

Epidemiology and Laboratory Diagnostics of Dengue, Yellow Fever, Zika, and Chikungunya Virus Infections in Africa

Arbovirus infections are widespread, and their disease burden has increased in the past decade. In Africa, arbovirus infections and fever with unknown etiology are common. Due to the lack of well-established epidemiologic surveillance systems and accurate differential diagnosis in most African countries, little is known about the prevalence of human arbovirus infections in Africa. The aim of this review is to summarize the available epidemiological data and diagnostic laboratory tools of infections with dengue, yellow fever, Zika, and chikungunya viruses, all transmitted by Aedes mosquitoes. Studies indicate that these arboviral infections are endemic in most of Africa. Surveillance of the incidence and prevalence of the infections would enable medical doctors to improve the diagnostic accuracy in patients with typical symptoms. If possible, arboviral diagnostic tests should be added to the routine healthcare systems. Healthcare providers should be informed about the prevalent arboviral diseases to identify possible cases.

Natural-Product-Based Solutions for Tropical Infectious Diseases

About half of the world's population and 80% of the world's biodiversity can be found in the tropics. Many diseases are specific to the tropics, with at least 41 diseases caused by endemic bacteria, viruses, parasites, and fungi. Such diseases are of increasing concern, as the geographic range of tropical diseases is expanding due to climate change, urbanization, change in agricultural practices, deforestation, and loss of biodiversity. While traditional medicines have been used for centuries in the treatment of tropical diseases, the active natural compounds within these medicines remain largely unknown. In this review, we describe infectious diseases specific to the tropics, including their causative pathogens, modes of transmission, recent major outbreaks, and geographic locations. We further review current treatments for these tropical diseases, carefully consider the biodiscovery potential of the tropical biome, and discuss a range of technologies being used for drug development from natural resources. We provide a list of natural products with antimicrobial activity, detailing the source organisms and their effectiveness as treatment. We discuss how technological advancements, such as next-generation sequencing, are driving high-throughput natural product screening pipelines to identify compounds with therapeutic properties. This review demonstrates the impact natural products from the vast tropical biome have in the treatment of tropical infectious diseases and how high-throughput technical capacity will accelerate this discovery process.

Modified Vaccinia Virus Ankara as a Viral Vector for Vaccine Candidates against Chikungunya Virus

There is a need to develop a highly effective vaccine against the emerging chikungunya virus (CHIKV), a mosquito-borne Alphavirus that causes severe disease in humans consisting of acute febrile illness, followed by chronic debilitating polyarthralgia and polyarthritis. In this review, we provide a brief history of the development of the first poxvirus vaccines that led to smallpox eradication and its implications for further vaccine development. As an example, we summarize the development of vaccine candidates based on the modified vaccinia virus Ankara (MVA) vector expressing different CHIKV structural proteins, paying special attention to MVA-CHIKV expressing all of the CHIKV structural proteins: C, E3, E2, 6K and E1. We review the characterization of innate and adaptive immune responses induced in mice and nonhuman primates by the MVA-CHIKV vaccine candidate and examine its efficacy in animal models, with promising preclinical findings needed prior to the approval of human clinical trials.

Mode-Dependent Antiviral Activity of Medicinal Plant Extracts against the Mosquito-Borne Chikungunya Virus

The lack of specific treatment for chikungunya fever makes the need for anti-chikungunya virus agents more crucial. This study was conducted to evaluate 132 extracts obtained by sequential solvent extraction from 21 medicinal plants for cytopathic effect inhibitory activity using virus-infected Vero cells in two different sample introduction modes. Among the extracts, 42 extracts (31.8%) from 12 plants in the concurrent mode and three extracts (2.3%) from a plant in the non-concurrent mode displayed strong cytopathic effect inhibitory activity (cell viability ≥70%). Viral load quantification analysis unveiled that the extracts of Clinacanthus nutans (chloroform, ethyl acetate, and ethanol), Hydrocotyle sibthorpioides (ethanol), and Ocimum americanum (ethanol and methanol) hindered the release of viral progeny from the infected cells while the extracts of Ficus deltoidea (ethanol), Gynura bicolor (water), H. sibthorpioides (water), and O. americanum (chloroform and ethyl acetate) blocked the entry of virus into the cells. The extracts of Diodella sarmentosa (ethyl acetate), Diplazium esculentum (chloroform, ethyl acetate, and ethanol), and G. bicolor (ethanol) possessed virucidal effect and caused 5.41-log to 6.63-log reductions of viral load compared to the virus control. The results indicate that these medicinal plants are potential sources of anti-chikungunya virus agents that have varied modes of action.

Interactions between capsid and viral RNA regulate Chikungunya virus translation in a host-specific manner

Alphaviruses are positive sense, RNA viruses commonly transmitted by an arthropod vector to a mammalian or avian host. In recent years, a number of the Alphavirus members have reemerged as public health concerns. Transmission from mosquito vector to vertebrate hosts requires an understanding of the interaction between the virus and both vertebrate and insect hosts to develop rational intervention strategies. The current study uncovers a novel role for capsid protein during Chikungunya virus replication whereby the interaction with viral RNA in the E1 coding region regulates protein synthesis processes early in infection. Studies done in both the mammalian and mosquito cells indicate that interactions between viral RNA and capsid protein have functional consequences that are host species specific. Our data support a vertebrate-specific role for capsid:vRNA interaction in temporally regulating viral translation in a manner dependent on the PI3K-AKT-mTOR pathway.

Current Status of Chikungunya in India

Chikungunya fever (CHIKF) is an arbovirus disease caused by chikungunya virus (CHIKV), an alphavirus of Togaviridae family. Transmission follows a human-mosquito-human cycle starting with a mosquito bite. Subsequently, symptoms develop after 2-6 days of incubation, including high fever and severe arthralgia. The disease is self-limiting and usually resolve within 2 weeks. However, chronic disease can last up to several years with persistent polyarthralgia. Overlapping symptoms and common vector with dengue and malaria present many challenges for diagnosis and treatment of this disease. CHIKF was reported in India in 1963 for the first time. After a period of quiescence lasting up to 32 years, CHIKV re-emerged in India in 2005. Currently, every part of the country has become endemic for the disease with outbreaks resulting in huge economic and productivity losses. Several mutations have been identified in circulating strains of the virus resulting in better adaptations or increased fitness in the vector(s), effective transmission, and disease severity. CHIKV evolution has been a significant driver of epidemics in India, hence, the need to focus on proper surveillance, and implementation of prevention and control measure in the country. Presently, there are no licensed vaccines or antivirals available; however, India has initiated several efforts in this direction including traditional medicines. In this review, we present the current status of CHIKF in India.

Ebola, Dengue, Chikungunya, and Zika Infections in Neonates and Infants

Emerging infectious diseases, including Ebola, chikungunya, Zika, and dengue, may have significant impacts on maternal-fetal dyads and neonatal outcomes. Pregnant women infected with Ebola demonstrate high mortality and very low evidence of neonatal survival. Maternal chikungunya infection can result in high rates of perinatal transmission, and infected neonates demonstrate variable disease severity. Dengue can be transmitted to neonates via vertical transmission or perinatal transmission. Zika is characterized by mild disease in pregnant women, but congenital infection can be severe. Treatment largely is supportive for these diseases, and vaccine development remains under way, with promising recent advances, notably for Ebola.

Ocular manifestations of emerging viral diseases

Emerging infectious diseases (EIDs) are an increasing threat to public health on a global scale. In recent times, the most prominent outbreaks have constituted RNA viruses, spreading via droplets (COVID-19 and Influenza A H1N1), directly between humans (Ebola and Marburg), via arthropod vectors (Dengue, Zika, West Nile, Chikungunya, Crimean Congo) and zoonotically (Lassa fever, Nipah, Rift Valley fever, Hantaviruses). However, specific approved antiviral therapies and vaccine availability are scarce, and public health measures remain critical. Patients can present with a spectrum of ocular manifestations. Emerging infectious diseases should therefore be considered in the differential diagnosis of ocular inflammatory conditions in patients inhabiting or returning from endemic territories, and more general vigilance is advisable in the context of a global pandemic. Eye specialists are in a position to facilitate swift diagnosis, improve clinical outcomes, and contribute to wider public health efforts during outbreaks. This article reviews those emerging viral diseases associated with reports of ocular manifestations and summarizes details pertinent to practicing eye specialists.

Nanocarrier vaccines for SARS-CoV-2

The SARS-CoV-2 global pandemic has seen rapid spread, disease morbidities and death associated with substantive social, economic and societal impacts. Treatments rely on re-purposed antivirals and immune modulatory agents focusing on attenuating the acute respiratory distress syndrome. No curative therapies exist. Vaccines remain the best hope for disease control and the principal global effort to end the pandemic. Herein, we summarize those developments with a focus on the role played by nanocarrier delivery.

Co-Immunization With CHIKV VLP and DNA Vaccines Induces a Promising Humoral Response in Mice

Chikungunya fever is an acute infectious disease that is mediated by the mosquito-transmitted chikungunya virus (CHIKV), for which no licensed vaccines are currently available. Here, we explored several immunization protocols and investigated their immunity and protective effects in mice, with DNA- and virus-like particle (VLP)- vaccines, both alone and in combination. Both DNA and VLP vaccine candidates were developed and characterized, which express CHIKV structural genes (C-E3-E2-6K-E1). Mice were immunized twice, with different protocols, followed by immunological detection and CHIKV Ross challenge. The highest antigen-specific IgG and neutralizing activity were induced by DNA and VLP co-immunization, while the highest cellular immunity was induced by DNA vaccination alone. Although all vaccine groups could protect mice from lethal CHIKV challenge, demonstrated as reduced viral load in various tissues, without weight loss, mice co-immunized with DNA and VLP exhibited the mildest histopathological changes and lowest International Harmonization of Nomenclature and Diagnostic Criteria (INHAND) scores, in comparison to mice with either DNA or VLP vaccination alone. We concluded that co-immunization with DNA and VLP is a promising strategy to inducing better protective immunity against CHIKV infection.

Legal and Health Response to COVID-19 in the Arab Countries

BACKGROUND

Arab countries account for almost 6% of the global population, yet they make up only 5% of the total cases and less than 3% of the global death toll attributed to COVID-19. COVID-19 has put the health systems in the various Arab Countries and their ability to deliver healthcare services under tremendous strain. The capacity and stability of any health system is important in any type of response to the pandemic, in order to ensure an effective and efficient delivery of care to the public through COVID-19 and beyond. The objective of this study is to identify the various response of health systems in Arab Countries to COVID-19, and highlight the legal and health challenges faced during the pandemic. The study identified both gaps and good practices that may be utilized in order to guide the efforts in response to COVID-19 and the recovery efforts once the pandemic is over.

METHODS

To determine why the response of some health systems in Arab Countries responses are more effective than others, a three-step framework is adopted which includes, detection, containment, and treatment stages. In order to identify which countries are excelling at detection, containment, and treatment stages, several indicators were selected for each stage. To be able to understand the legal and health challenges of response to the COVID-19 pandemic, an analysis of the health systems, the resources in terms of quality and access, health workforce, and finance was conducted. Secondary data published by the Global Burden of Disease Study, and the Global Change Data Lab of the University of Oxford was used to study identified gaps and good practices to guide the responses to COVID-19 and recovery efforts once the pandemic is over.

RESULTS

The epidemiologic record demonstrates that that certain Arab countries are managing to control the pandemic, through a combination of mitigation strategies, suppression strategy and elimination strategy. There are several barriers and challenges in Arab health systems which have been amplified due to COVID-19 and if ignored may pose a further significant challenge in the future. Health systems in Arab countries are not sufficiently equipped to handle all healthcare needs related to COVID-19, in particular issues relating to administration, equity, finances, the supply side of healthcare, and usage of information technology.

CONCLUSION

In Arab counties, the standard response to COVID-19 was enforced by new health laws, which consist of a combination of the traditional disease control measures (testing, contact-tracing, social distancing), population-based physical distancing (including stay-at-home orders, school and business closures, and social gathering bans), travel limits (including travel bans, and border closures), and economic support measures. Acceptable healthcare quality and access, sufficient health workforce, and sufficient funds are the most imperative needs in the health system in Arab counties to provide a sustainable response to the COVID-19 pandemic.

Perspectives on New Vaccines against Arboviruses Using Insect-Specific Viruses as Platforms

Arthropod-borne viruses (arboviruses) are global pathogens circulating endemically with local explosive outbreaks and constant encroachment into new locations. Few vaccines against arboviruses exist; most for humans are in development or clinical trials. Insect-specific viruses (ISVs) offer a unique platform for expression of arbovirus proteins, through the creation of ISV/arbovirus chimeras. Studies have shown promising results of these vaccines with several advantages over their wild-type counterparts. In this review, we discuss the current status of these potential vaccines using ISVs.

Arbovirus Rash in the Febrile Returning Traveler as a Diagnostic Clue

Purpose of Review

This review aims to describe briefly the general information of arboviruses dengue, Zika, and chikungunya infections and emphasize the clinical manifestations of each, to help identify and make a quick diagnosis of each.

Recent Findings

The most relevant advances in the study of these arboviruses’ infections have been in the epidemiological distribution, mainly due to international travel, migration, and climate change; in the clinical manifestations of these diseases, the development of clinical decision-making software, which can help improve the management and outcomes of these patients; and in the prevention of this disease.

Summary

Although arboviruses infections constitute a clinical challenge for the attending physician in the scope of a febrile returning traveler, a thorough clinical history and exam can help to aid diagnostic reasoning. The characteristics of the rash are a very helpful clue in the evaluation of these patients. Currently, there are clinical decision aid tools that help to get the diagnosis more quickly.

A phase 1 trial of lipid-encapsulated mRNA encoding a monoclonal antibody with neutralizing activity against Chikungunya virus

Chikungunya virus (CHIKV) infection causes acute disease characterized by fever, rash and arthralgia, which progresses to severe and chronic arthritis in up to 50% of patients. Moreover, CHIKV infection can be fatal in infants or immunocompromised individuals and has no approved therapy or prevention. This phase 1, first-in-human, randomized, placebo-controlled, proof-of-concept trial conducted from January 2019 to June 2020 evaluated the safety and pharmacology of mRNA-1944, a lipid nanoparticle-encapsulated messenger RNA encoding the heavy and light chains of a CHIKV-specific monoclonal neutralizing antibody, CHKV-24 ( NCT03829384 ). The primary outcome was to evaluate the safety and tolerability of escalating doses of mRNA-1944 administered via intravenous infusion in healthy participants aged 18-50 years. The secondary objectives included determination of the pharmacokinetics of mRNA encoding for CHKV-24 immunoglobulin heavy and light chains and ionizable amino lipid component and the pharmacodynamics of mRNA-1944 as assessed by serum concentrations of mRNA encoding for CHKV-24 immunoglobulin G (IgG), plasma concentrations of ionizable amino lipid and serum concentrations of CHKV-24 IgG. Here we report the results of a prespecified interim analysis of 38 healthy participants who received intravenous single doses of mRNA-1944 or placebo at 0.1, 0.3 and 0.6 mg kg^-1, or two weekly doses at 0.3 mg kg^-1. At 12, 24 and 48 h after single infusions, dose-dependent levels of CHKV-24 IgG with neutralizing activity were observed at titers predicted to be therapeutically relevant concentrations (≥1 µg ml^-1) across doses that persisted for ≥16 weeks at 0.3 and 0.6 mg kg^-1 (mean t_1/2 approximately 69 d). A second 0.3 mg kg^-1 dose 1 week after the first increased CHKV-24 IgG levels 1.8-fold. Adverse effects were mild to moderate in severity, did not worsen with a second mRNA-1944 dose and none were serious. To our knowledge, mRNA-1944 is the first mRNA-encoded monoclonal antibody showing in vivo expression and detectable ex vivo neutralizing activity in a clinical trial and may offer a treatment option for CHIKV infection. Further evaluation of the potential therapeutic use of mRNA-1944 in clinical trials for the treatment of CHIKV infection is warranted.

Novel insights into the treatment of SARS-CoV-2 infection: An overview of current clinical trials

The emergence of the global pandemic caused by the novel SARS-CoV-2 virus has motivated scientists to find a definitive treatment or a vaccine against it in the shortest possible time. Current efforts towards this goal remain fruitless without a full understanding of the behavior of the virus and its adaptor proteins. This review provides an overview of the biological properties, functional mechanisms, and molecular components of SARS-CoV-2, along with investigational therapeutic and preventive approaches for this virus. Since the proteolytic cleavage of the S protein is critical for virus penetration into cells, a set of drugs, such as chloroquine, hydroxychloroquine, camostat mesylate have been tested in clinical trials to suppress this event. In addition to angiotensin-converting enzyme 2, the role of CD147 in the viral entrance has also been proposed. Mepolizumab has shown to be effective in blocking the virus's cellular entrance. Antiviral drugs, such as remdesivir, ritonavir, oseltamivir, darunavir, lopinavir, zanamivir, peramivir, and oseltamivir, have also been tested as treatments for COVID-19. Regarding preventive vaccines, the whole virus, vectors, nucleic acids, and structural subunits have been suggested for vaccine development. Mesenchymal stem cells and natural killer cells could also be used against SARS-CoV-2. All the above-mentioned strategies, as well as the role of nanomedicine for the diagnosis and treatment of SARS-CoV-2 infection, have been discussed in this review.

Viral Emerging Diseases: Challenges in Developing Vaccination Strategies

In the last decades, a number of infectious viruses have emerged from wildlife or re-emerged, generating serious threats to the global health and to the economy worldwide. Ebola and Marburg hemorrhagic fevers, Lassa fever, Dengue fever, Yellow fever, West Nile fever, Zika, and Chikungunya vector-borne diseases, Swine flu, Severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and the recent Coronavirus disease 2019 (COVID-19) are examples of zoonoses that have spread throughout the globe with such a significant impact on public health that the scientific community has been called for a rapid intervention in preventing and treating emerging infections. Vaccination is probably the most effective tool in helping the immune system to activate protective responses against pathogens, reducing morbidity and mortality, as proven by historical records. Under health emergency conditions, new and alternative approaches in vaccine design and development are imperative for a rapid and massive vaccination coverage, to manage a disease outbreak and curtail the epidemic spread. This review gives an update on the current vaccination strategies for some of the emerging/re-emerging viruses, and discusses challenges and hurdles to overcome for developing efficacious vaccines against future pathogens.

An overview of COVID-19

Pneumonia caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection emerged in Wuhan City, Hubei Province, China in December 2019. By Feb. 11, 2020, the World Health Organization (WHO) officially named the disease resulting from infection with SARS-CoV-2 as coronavirus disease 2019 (COVID-19). COVID-19 represents a spectrum of clinical manifestations that typically include fever, dry cough, and fatigue, often with pulmonary involvement. SARS-CoV-2 is highly contagious and most individuals within the population at large are susceptible to infection. Wild animal hosts and infected patients are currently the main sources of disease which is transmitted via respiratory droplets and direct contact. Since the outbreak, the Chinese government and scientific community have acted rapidly to identify the causative agent and promptly shared the viral gene sequence, and have carried out measures to contain the epidemic. Meanwhile, recent research has revealed critical aspects of SARS-CoV-2 biology and disease pathogenesis; other studies have focused on epidemiology, clinical features, diagnosis, management, as well as drug and vaccine development. This review aims to summarize the latest research findings and to provide expert consensus. We will also share ongoing efforts and experience in China, which may provide insight on how to contain the epidemic and improve our understanding of this emerging infectious disease, together with updated guidance for prevention, control, and critical management of this pandemic.