Immunogenicity of calvenza‐03 eiv/ehv® vaccine in horses: Comparative in vivo study

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.