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Elliott S, Olufemi OT, Daly JM. Systematic Review of Equine Influenza A Virus Vaccine Studies and Meta-Analysis of Vaccine Efficacy. Viruses 2023; 15:2337. [PMID: 38140577 PMCID: PMC10747572 DOI: 10.3390/v15122337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2023] [Revised: 11/21/2023] [Accepted: 11/23/2023] [Indexed: 12/24/2023] Open
Abstract
Vaccines against equine influenza have been available since the late 1960s, but outbreaks continue to occur periodically, affecting both vaccinated and unvaccinated animals. The aim of this study was to systematically evaluate the efficacy of vaccines against influenza A virus in horses (equine IAV). For this, PubMed, CAB abstracts, and Web of Science were searched for controlled trials of equine IAV vaccines published up to December 2020. Forty-three articles reporting equine IAV vaccination and challenge studies in previously naïve equids using an appropriate comparison group were included in a qualitative analysis of vaccine efficacy. A value for vaccine efficacy (VE) was calculated as the percentage reduction in nasopharyngeal virus shedding detected by virus isolation in embryonated hens' eggs from 38 articles. Among 21 studies involving commercial vaccines, the mean VE was 50.03% (95% CI: 23.35-76.71%), ranging from 0 to 100%. Among 17 studies reporting the use of experimental vaccines, the mean VE was 40.37% (95% CI: 19.64-62.44), and the range was again 0-100%. Overall, complete protection from virus shedding was achieved in five studies. In conclusion, although commercially available vaccines can, in some circumstances, offer complete protection from infection, the requirement for frequent vaccination in the field to limit virus shedding and hence transmission is apparent. Although most studies were conducted by a few centres, a lack of consistent study design made comparisons difficult.
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Affiliation(s)
| | | | - Janet M. Daly
- One Virology, Wolfson Centre for Global Virus Research, School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington LE12 5RD, UK
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Chiem K, Park JG, Morales Vasquez D, Plemper RK, Torrelles JB, Kobie JJ, Walter MR, Ye C, Martinez-Sobrido L. Monitoring SARS-CoV-2 Infection Using a Double Reporter-Expressing Virus. Microbiol Spectr 2022; 10:e0237922. [PMID: 35980204 PMCID: PMC9603146 DOI: 10.1128/spectrum.02379-22] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 08/02/2022] [Indexed: 01/04/2023] Open
Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the highly contagious agent responsible for the coronavirus disease 2019 (COVID-19) pandemic. An essential requirement for understanding SARS-CoV-2 biology and the impact of antiviral therapeutics is a robust method to detect the presence of the virus in infected cells or animal models. Despite the development and successful generation of recombinant (r)SARS-CoV-2-expressing fluorescent or luciferase reporter genes, knowledge acquired from their use in in vitro assays and/or in live animals is limited to the properties of the fluorescent or luciferase reporter genes. Herein, for the first time, we engineered a replication-competent rSARS-CoV-2 that expresses both fluorescent (mCherry) and luciferase (Nluc) reporter genes (rSARS-CoV-2/mCherry-Nluc) to overcome limitations associated with the use of a single reporter gene. In cultured cells, rSARS-CoV-2/mCherry-Nluc displayed similar viral fitness as rSARS-CoV-2 expressing single reporter fluorescent and luciferase genes (rSARS-CoV-2/mCherry and rSARS-CoV-2/Nluc, respectively) or wild-type (WT) rSARS-CoV-2, while maintaining comparable expression levels of both reporter genes. In vivo, rSARS-CoV-2/mCherry-Nluc has similar pathogenicity in K18 human angiotensin-converting enzyme 2 (hACE2) transgenic mice than rSARS-CoV-2 expressing individual reporter genes or WT rSARS-CoV-2. Importantly, rSARS-CoV-2/mCherry-Nluc facilitates the assessment of viral infection and transmission in golden Syrian hamsters using in vivo imaging systems (IVIS). Altogether, this study demonstrates the feasibility of using this novel bioreporter-expressing rSARS-CoV-2 for the study of SARS-CoV-2 in vitro and in vivo. IMPORTANCE Despite the availability of vaccines and antivirals, the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to ravage health care institutions worldwide. Previously, we generated replication-competent recombinant (r)SARS-CoV-2 expressing fluorescent or luciferase reporter proteins to track viral infection in vitro and/or in vivo. However, these rSARS-CoV-2 are restricted to express only a single fluorescent or a luciferase reporter gene, limiting or preventing their use in specific in vitro assays and/or in vivo studies. To overcome this limitation, we have engineered a rSARS-CoV-2 expressing both fluorescent (mCherry) and luciferase (Nluc) genes and demonstrated its feasibility to study the biology of SARS-CoV-2 in vitro and/or in vivo, including the identification and characterization of neutralizing antibodies and/or antivirals. Using rodent models, we visualized SARS-CoV-2 infection and transmission through in vivo imaging systems (IVIS).
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Affiliation(s)
- Kevin Chiem
- Texas Biomedical Research Institute, San Antonio, Texas, USA
| | - Jun-Gyu Park
- Texas Biomedical Research Institute, San Antonio, Texas, USA
| | | | - Richard K. Plemper
- Center for Translational Antiviral Research, Institute for Biomedical Sciences, Georgia State University, Atlanta, Georgia, USA
| | | | - James J. Kobie
- Department of Medicine, Division of Infectious Diseases, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Mark R. Walter
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Chengjin Ye
- Texas Biomedical Research Institute, San Antonio, Texas, USA
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Nogales A, Steel J, Liu WC, Lowen AC, Rodriguez L, Chiem K, Cox A, García-Sastre A, Albrecht RA, Dewhurst S, Martínez-Sobrido L. Mutation L319Q in the PB1 Polymerase Subunit Improves Attenuation of a Candidate Live-Attenuated Influenza A Virus Vaccine. Microbiol Spectr 2022; 10:e0007822. [PMID: 35583364 PMCID: PMC9241597 DOI: 10.1128/spectrum.00078-22] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Accepted: 04/25/2022] [Indexed: 01/11/2023] Open
Abstract
Influenza A viruses (IAV) remain emerging threats to human public health. Live-attenuated influenza vaccines (LAIV) are one of the most effective prophylactic options to prevent disease caused by influenza infections. However, licensed LAIV remain restricted for use in 2- to 49-year-old healthy and nonpregnant people. Therefore, development of LAIV with increased safety, immunogenicity, and protective efficacy is highly desired. The U.S.-licensed LAIV is based on the master donor virus (MDV) A/Ann Arbor/6/60 H2N2 backbone, which was generated by adaptation of the virus to growth at low temperatures. Introducing the genetic signature of the U.S. MDV into the backbone of other IAV strains resulted in varying levels of attenuation. While the U.S. MDV mutations conferred an attenuated phenotype to other IAV strains, the same amino acid changes did not significantly attenuate the pandemic A/California/04/09 H1N1 (pH1N1) strain. To attenuate pH1N1, we replaced the conserved leucine at position 319 with glutamine (L319Q) in PB1 and analyzed the in vitro and in vivo properties of pH1N1 viruses containing either PB1 L319Q alone or in combination with the U.S. MDV mutations using two animal models of influenza infection and transmission, ferrets and guinea pigs. Our results demonstrated that L319Q substitution in the pH1N1 PB1 alone or in combination with the mutations of the U.S. MDV resulted in reduced pathogenicity (ferrets) and transmission (guinea pigs), and an enhanced temperature sensitive phenotype. These results demonstrate the feasibility of generating an attenuated MDV based on the backbone of a contemporary pH1N1 IAV strain. IMPORTANCE Vaccination represents the most effective strategy to reduce the impact of seasonal IAV infections. Although LAIV are superior in inducing protection and sterilizing immunity, they are not recommended for many individuals who are at high risk for severe disease. Thus, development of safer and more effective LAIV are needed. A concern with the current MDV used to generate the U.S.-licensed LAIV is that it is based on a virus isolated in 1960. Moreover, mutations that confer the temperature-sensitive, cold-adapted, and attenuated phenotype of the U.S. MDV resulted in low level of attenuation in the contemporary pandemic A/California/04/09 H1N1 (pH1N1). Here, we show that introduction of PB1 L319Q substitution, alone or in combination with the U.S. MDV mutations, resulted in pH1N1 attenuation. These findings support the development of a novel LAIV MDV based on a contemporary pH1N1 strain as a medical countermeasure against currently circulating H1N1 IAV.
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Affiliation(s)
- Aitor Nogales
- Department of Microbiology and Immunology, School of Medicine and Dentistry, University of Rochester, Rochester, New York, USA
- Animal Health Research Centre (CISA), Centro Nacional Instituto de Investigación y Tecnología Agraria y Alimentaria (INIA, CSIC), Madrid, Spain
| | - John Steel
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Wen-Chun Liu
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA
- Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
- Biomedical Translation Research Center, Academia Sinica, Taipei, Taiwan
| | - Anice C. Lowen
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Laura Rodriguez
- Department of Microbiology and Immunology, School of Medicine and Dentistry, University of Rochester, Rochester, New York, USA
- Agencia Española de Medicamentos y Productos Sanitarios, Madrid, Spain
| | - Kevin Chiem
- Department of Microbiology and Immunology, School of Medicine and Dentistry, University of Rochester, Rochester, New York, USA
- Texas Biomedical Research Institute, San Antonio, Texas, USA
| | - Andrew Cox
- Department of Microbiology and Immunology, School of Medicine and Dentistry, University of Rochester, Rochester, New York, USA
| | - Adolfo García-Sastre
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA
- Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
- Department of Medicine, Division of Infectious Diseases, Icahn School of Medicine at Mount Sinai, New York, New York, USA
- The Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
- Department of Pathology, Molecular and Cell-Based Medicine, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Randy A. Albrecht
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA
- Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Stephen Dewhurst
- Department of Microbiology and Immunology, School of Medicine and Dentistry, University of Rochester, Rochester, New York, USA
| | - Luis Martínez-Sobrido
- Department of Microbiology and Immunology, School of Medicine and Dentistry, University of Rochester, Rochester, New York, USA
- Texas Biomedical Research Institute, San Antonio, Texas, USA
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Experimental Infection of Horses with Influenza D Virus. Viruses 2022; 14:v14040661. [PMID: 35458390 PMCID: PMC9029652 DOI: 10.3390/v14040661] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Revised: 03/19/2022] [Accepted: 03/20/2022] [Indexed: 02/04/2023] Open
Abstract
Antibodies to influenza D virus (IDV) have been detected in horses, but no evidence of disease in the field has been reported. To determine whether IDV is infectious, immunogenic, and pathogenic in horses, four 2-year-old horses seronegative for both influenza A (H3N8) and D viruses were intranasally inoculated with 6.25 × 107 TCID50/animal of D/bovine/California/0363/2019 (D/CA2019) virus, using a portable equine nebulizer system. Horses were observed daily for clinical signs including rectal temperature, nasal discharge, coughing, lung sounds, tachycardia, and tachypnea. No horses exhibited clinical signs of disease. Nasopharyngeal swabs collected from 1–8 days post-infection demonstrated virus shedding by qRT-PCR. The horses showed evidence of seroconversion as early as 13 days post-infection (dpi) and the geometric mean of the antibody titers (GMT) of all four horses ranged from 16.82–160 as demonstrated by the microneutralization assay. Further, deep RNA sequencing of the virus isolated in embryonated chicken eggs revealed no adaptive mutations indicating that IDV can replicate in horses, suggesting the possibility of interspecies transmission of IDV with bovine reservoir into equids in nature.
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Equine Influenza Virus and Vaccines. Viruses 2021; 13:v13081657. [PMID: 34452521 PMCID: PMC8402878 DOI: 10.3390/v13081657] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 07/27/2021] [Accepted: 07/28/2021] [Indexed: 01/01/2023] Open
Abstract
Equine influenza virus (EIV) is a constantly evolving viral pathogen that is responsible for yearly outbreaks of respiratory disease in horses termed equine influenza (EI). There is currently no evidence of circulation of the original H7N7 strain of EIV worldwide; however, the EIV H3N8 strain, which was first isolated in the early 1960s, remains a major threat to most of the world's horse populations. It can also infect dogs. The ability of EIV to constantly accumulate mutations in its antibody-binding sites enables it to evade host protective immunity, making it a successful viral pathogen. Clinical and virological protection against EIV is achieved by stimulation of strong cellular and humoral immunity in vaccinated horses. However, despite EI vaccine updates over the years, EIV remains relevant, because the protective effects of vaccines decay and permit subclinical infections that facilitate transmission into susceptible populations. In this review, we describe how the evolution of EIV drives repeated EI outbreaks even in horse populations with supposedly high vaccination coverage. Next, we discuss the approaches employed to develop efficacious EI vaccines for commercial use and the existing system for recommendations on updating vaccines based on available clinical and virological data to improve protective immunity in vaccinated horse populations. Understanding how EIV biology can be better harnessed to improve EI vaccines is central to controlling EI.
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A New Master Donor Virus for the Development of Live-Attenuated Influenza B Virus Vaccines. Viruses 2021; 13:v13071278. [PMID: 34208979 PMCID: PMC8310163 DOI: 10.3390/v13071278] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2021] [Revised: 06/27/2021] [Accepted: 06/27/2021] [Indexed: 12/23/2022] Open
Abstract
Influenza B viruses (IBV) circulate annually, with young children, the elderly and immunocompromised individuals being at high risk. Yearly vaccinations are recommended to protect against seasonally influenza viruses, including IBV. Live attenuated influenza vaccines (LAIV) provide the unique opportunity for direct exposure to the antigenically variable surface glycoproteins as well as the more conserved internal components. Ideally, LAIV Master Donor Viruses (MDV) should accurately reflect seasonal influenza strains. Unfortunately, the continuous evolution of IBV have led to significant changes in conserved epitopes compared to the IBV MDV based on B/Ann Arbor/1/1966 strain. Here, we propose a recent influenza B/Brisbane/60/2008 as an efficacious MDV alternative, as its internal viral proteins more accurately reflect those of circulating IBV strains. We introduced the mutations responsible for the temperature sensitive (ts), cold adapted (ca) and attenuated (att) phenotype of B/Ann Arbor/1/1966 MDV LAIV into B/Brisbane/60/2008 to generate a new MDV LAIV. In vitro and in vivo analysis demonstrated that the mutations responsible of the ts, ca, and att phenotype of B/Ann Arbor/1/1966 MDV LAIV were able to infer the same phenotype to B/Brisbane/60/2008, demonstrating its potential as a new MDV for the development of LAIV to protect against contemporary IBV strains.
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Pavulraj S, Bergmann T, Trombetta CM, Marchi S, Montomoli E, Alami SSE, Ragni-Alunni R, Osterrieder N, Azab W. Immunogenicity of Calvenza-03 EIV/EHV ® Vaccine in Horses: Comparative In Vivo Study. Vaccines (Basel) 2021; 9:vaccines9020166. [PMID: 33671378 PMCID: PMC7922102 DOI: 10.3390/vaccines9020166] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 02/10/2021] [Accepted: 02/12/2021] [Indexed: 01/20/2023] Open
Abstract
Equine influenza (EI) is a highly contagious acute respiratory disease of equines that is caused mainly by the H3N8 subtype of influenza A virus. Vaccinating horses against EI is the most effective strategy to prevent the infection. The current study aimed to compare the kinetics of EI-specific humoral- and cell-mediated immunity (CMI) in horses receiving either identical or mixed vaccinations. Two groups of horses were previously (six months prior) vaccinated with either Calvenza 03 EIV EHV® (G1) or Fluvac Innovator® (G2) vaccine. Subsequently, both groups received a booster single dose of Calvenza 03 EIV EHV®. Immune responses were assessed after 10 weeks using single radial hemolysis (SRH), virus neutralization (VN), and EliSpot assays. Our results revealed that Calvenza-03 EIV/EHV®-immunized horses had significantly higher protective EI-specific SRH antibodies and VN antibodies. Booster immunization with Calvenza-03 EIV/EHV® vaccine significantly stimulated cell-mediated immune response as evidenced by significant increase in interferon-γ-secreting peripheral blood mononuclear cells. In conclusion, Calvenza-03 EIV/EHV® vaccine can be safely and effectively used for booster immunization to elicit optimal long persisting humoral and CMI responses even if the horses were previously immunized with a heterogeneous vaccine.
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Affiliation(s)
- Selvaraj Pavulraj
- Institut für Virologie, Robert von Ostertag-Haus, Zentrum für Infektionsmedizin, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany; (S.P.); (T.B.); (N.O.)
| | - Tobias Bergmann
- Institut für Virologie, Robert von Ostertag-Haus, Zentrum für Infektionsmedizin, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany; (S.P.); (T.B.); (N.O.)
| | - Claudia Maria Trombetta
- Department of Molecular and Developmental Medicine, University of Siena, 53100 Siena, Italy; (C.M.T.); (S.M.); (E.M.)
| | - Serena Marchi
- Department of Molecular and Developmental Medicine, University of Siena, 53100 Siena, Italy; (C.M.T.); (S.M.); (E.M.)
| | - Emanuele Montomoli
- Department of Molecular and Developmental Medicine, University of Siena, 53100 Siena, Italy; (C.M.T.); (S.M.); (E.M.)
- VisMederi srl, 53100 Siena, Italy
| | | | - Roberto Ragni-Alunni
- Equine Marketing Division, Boehringer Ingelheim META, Dubai P.O. Box 507066, United Arab Emirates;
| | - Nikolaus Osterrieder
- Institut für Virologie, Robert von Ostertag-Haus, Zentrum für Infektionsmedizin, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany; (S.P.); (T.B.); (N.O.)
- Department of Infectious Diseases and Public Health, Jockey Club College of Veterinary Medicine and Life Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong 999077, China
| | - Walid Azab
- Institut für Virologie, Robert von Ostertag-Haus, Zentrum für Infektionsmedizin, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany; (S.P.); (T.B.); (N.O.)
- Correspondence:
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Ohta M, Bannai H, Kambayashi Y, Tamura N, Tsujimura K, Yamayoshi S, Kawaoka Y, Nemoto M. Growth properties and immunogenicity of a virus generated by reverse genetics for an inactivated equine influenza vaccine. Equine Vet J 2021; 54:139-144. [PMID: 33527477 DOI: 10.1111/evj.13431] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Revised: 01/09/2021] [Accepted: 01/22/2021] [Indexed: 12/01/2022]
Abstract
BACKGROUND Keeping vaccine strains up to date is the key to controlling equine influenza (EI). Viruses generated by reverse genetics (RG) are likely to be effective for quickly updating a vaccine strain. OBJECTIVES To evaluate the growth properties of an RG virus in embryonated chicken eggs, and to evaluate antibody responses to a formalin-inactivated vaccine derived from the RG virus in Thoroughbred horses. STUDY DESIGN In vitro and in vivo experiments. METHODS Wild-type (WT) viruses (A/equine/Ibaraki/1/2007) or RG viruses (consisting of haemagglutinin [HA] and neuraminidase genes derived from A/equine/Ibaraki/1/2007 and the six other genes derived from high-growth A/Puerto Rico/8/34) were inoculated into embryonated chicken eggs, and the allantoic fluids were harvested at every 24 hours after inoculation. WT and RG viruses were inactivated by formalin for vaccine use. Ten unvaccinated yearlings (five each for WT or RG vaccine) received the first two doses of a primary vaccination course 4 weeks apart followed by their third dose 12 weeks later. Twenty vaccinated adult horses (10 each for WT or RG vaccine) received a single dose of a booster vaccination. RESULTS The RG virus had high growth properties in embryonated chicken eggs. Unvaccinated yearlings responded poorly to the first vaccination, especially those that received the RG vaccine, but mounted better responses to the second and the third vaccinations, and maintained relatively high haemagglutination inhibition (HI) titres up to 28 weeks after the first vaccination. Vaccinated adult horses did not respond remarkably to the booster vaccination, but no horses showed titres below their pre-booster values even at 12 weeks after vaccination. The RG virus elicited immunogenicity in horses adequate for vaccine use. MAIN LIMITATIONS No virus challenge study was performed. CONCLUSIONS The RG viruses are useful as an EI vaccine strain, and quick updates of an EI vaccine strain can be achieved by using RG techniques.
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Affiliation(s)
- Minoru Ohta
- Molecular Biology Division, Equine Research Institute, Japan Racing Association, Tochigi, Japan
| | - Hiroshi Bannai
- Molecular Biology Division, Equine Research Institute, Japan Racing Association, Tochigi, Japan
| | - Yoshinori Kambayashi
- Molecular Biology Division, Equine Research Institute, Japan Racing Association, Tochigi, Japan
| | - Norihisa Tamura
- Clinical Veterinary Medicine Division, Equine Research Institute, Japan Racing Association, Tochigi, Japan
| | - Koji Tsujimura
- Molecular Biology Division, Equine Research Institute, Japan Racing Association, Tochigi, Japan
| | - Seiya Yamayoshi
- Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan
| | - Yoshihiro Kawaoka
- Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.,Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI, USA
| | - Manabu Nemoto
- Molecular Biology Division, Equine Research Institute, Japan Racing Association, Tochigi, Japan
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