Antigenic differences between equine influenza virus vaccine strains and Florida sublineage clade 1 strains isolated in Europe in 2019.
Authors: Nemoto Manabu, Ohta Minoru, Yamanaka Takashi, Kambayashi Yoshinori, Bannai Hiroshi, Tsujimura Koji, Yamayoshi Seiya, Kawaoka Yoshihiro, Cullinane Ann
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Equine Influenza Vaccine Efficacy Against Emerging European Strains Between 2018 and 2019, Florida sublineage clade 1 (Fc1) equine influenza viruses—previously confined largely to the United States—unexpectedly emerged across Europe, prompting concerns about vaccine coverage; this study examined whether current OIE-recommended vaccine strains retain adequate neutralising capacity against these novel European isolates. Researchers generated virus neutralisation assays using horse antisera collected after experimental infection with the vaccine reference strains A/equine/South Africa/4/2003 (used internationally) and A/equine/Ibaraki/2007 (used in Japanese vaccines), then tested these sera against the naturally occurring Irish strain A/equine/Tipperary/1/2019, a British strain A/equine/Essex/1/2019, and recombinant viruses expressing their surface glycoproteins. Antibody titres against all three 2019 European isolates were substantially reduced—between 2.5- and 6.3-fold lower than homologous responses—indicating meaningful antigenic drift within the circulating Fc1 population. Although current vaccines still generated cross-protective neutralising antibodies against the 2019 strains, the magnitude of reduction signals that ongoing viral evolution warrants continuous surveillance and periodic reassessment of vaccine strain selection to maintain optimal immune coverage and prevent further attenuation of field protection.
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Practical Takeaways
- •Current EIV vaccines provide some protection against 2019 European strains, but reduced antibody responses suggest vaccine efficacy may be compromised; consider supplementary vaccination strategies if exposure risk is high
- •The gap between vaccine strains (2003-2007) and circulating strains (2019) demonstrates the need for regular vaccine updates; work with your veterinarian to ensure your vaccination protocol includes the most current recommended strains
- •Implement rigorous biosecurity and health monitoring protocols, as vaccine protection against newer strains may not be optimal; stay informed of OIE vaccine recommendations which are periodically updated based on circulating virus surveillance
Key Findings
- •Antibody titers against 2019 European Fc1 strains (A/equine/Tipperary/1/2019 and A/equine/Essex/1/2019) were 2.5- to 6.3-fold lower than against vaccine strains A/equine/South Africa/4/2003 or A/equine/Ibaraki/2007
- •Current vaccine strains still neutralize 2019 European Fc1 strains despite antigenic drift, but protection may be reduced
- •Florida sublineage clade 1 viruses have undergone antigenic evolution since the 2003-2007 vaccine strain derivation, warranting ongoing surveillance for vaccine strain selection