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Impact of Mixed Equine Influenza Vaccination on Correlate of Protection in Horses

Department of Medicine, Surgery and Reproduction, Hassan II Institute for Agronomy and Veterinary Medicine, Rabat-Institutes 10101, Morocco
M.C.I Animal Health—Lot 157, ZI South-West P.O. Box 278, Mohammedia 28810, Morocco
Normandie Univ, UniCaen, Biotargen, 3 rue Nelson Mandela, 14280 Saint-Contest, France
LABÉO Frank Duncombe, 1 route de Rosel, 14053 Caen CEDEX 4, France
Department of Statistics and Applied Informatics, Agronomic and Veterinary Institute Hassan II, Rabat-Institutes 10101, Morocco
Department of Microbiology, Immunology and Contagious Diseases, Agronomic and Veterinary Institute Hassan II-B.P 6202 Rabat-Institutes, Rabat-Institutes 10101, Morocco
Author to whom correspondence should be addressed.
Vaccines 2018, 6(4), 71;
Received: 8 August 2018 / Revised: 6 September 2018 / Accepted: 14 September 2018 / Published: 4 October 2018
PDF [492 KB, uploaded 4 October 2018]


To evaluate the humoral immune response to mixed Equine Influenza vaccination, a common practice in the field, an experimental study was carried out on 42 unvaccinated thoroughbred weanling foals divided into six groups of seven. Three groups were vaccinated using a non-mixed protocol (Equilis® Prequenza-Te, Proteqflu-Te® or Calvenza-03®) and three other groups were vaccinated using a mix of the three vaccines mentioned previously. Each weanling underwent a primary EI vaccination schedule composed of two primary immunisations (V1 and V2) four weeks apart followed by a third boost immunisation (V3) six months later. Antibody responses were monitored until one-year post-V3 by single radial haemolysis (SRH). The results showed similar antibody responses for all groups using mixed EI vaccination and the group exclusively vaccinated with Equilis® Prequenza-TE, which were significantly higher than the other two groups vaccinated with Proteqflu-TE® and Calvenza-03®. All weanlings (100%) failed to seroconvert after V1 and 21% (9/42) still had low or no SRH antibody titres two weeks post-V2. All weanlings had seroconverted and exceeded the clinical protection threshold one month after V3. The poor response to vaccination was primarily observed in groups exclusively vaccinated with Proteqflu-Te® and Calvenza-03®. A large window of susceptibility (3–4.5-month duration) usually called immunity gap was observed after V2 and prior to V3 for all groups. The SRH antibody level was maintained above the clinical protection threshold for three months post-V3 for the groups exclusively vaccinated with Proteqflu-Te® and Calvenza-03®, and six months to one year for groups using mixed EI vaccination or exclusively vaccinated with Equilis® Prequenza-Te. This study demonstrates for the first time that the mix of EI vaccines during the primary vaccination schedule has no detrimental impact on the correlate of protection against EIV infection. View Full-Text
Keywords: equine influenza; vaccination; antibody; SRH; comparison; mixed vaccination equine influenza; vaccination; antibody; SRH; comparison; mixed vaccination

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Dilai, M.; Piro, M.; El Harrak, M.; Fougerolle, S.; Dehhaoui, M.; Dikrallah, A.; Legrand, L.; Paillot, R.; Fassi Fihri, O. Impact of Mixed Equine Influenza Vaccination on Correlate of Protection in Horses. Vaccines 2018, 6, 71.

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