Success and Limitation of Equine Influenza Vaccination: The First Incursion in a Decade of a Florida Clade 1 Equine Influenza Virus that Shakes Protection Despite High Vaccine Coverage

Stéphanie Fougerolle (1, 2) , Christine Fortier (1, 2) , Loïc Legrand (1, 2) , Marion Jourdan (3) , Christel Marcillaud Pitel (3) , Stéphane Pronost (1, 2) , Romain Paillot (1, 2)

1 LABÉO - LABÉO, Pôle d’analyses et de recherche de Normandie
2 BIOTARGEN - Biologie, génétique et thérapies ostéoarticulaires et respiratoires
3 RESPE - Réseau d'Epidémio-Surveillance en Pathologie Équine

Every year, several epizooties of equine influenza (EI) are reported worldwide. However, noEI case has been identified in France between 2015 and late 2018, despite an effective field surveillanceof the pathogen and the disease. Vaccination against equine influenza virus (EIV) remains to thisday one of the most effective methods to prevent or limit EI outbreaks and the lack of detectionof the pathogen could be linked to vaccination coverage. The aim of this study was to evaluateEI immunity and vaccine coverage in France through a large-scale serological study. A total of3004 archived surplus serums from French horses of all ages, breeds and sexes were selected fromfour different geographical regions and categories (i.e., sanitary check prior to exportation, sale,breeding protocol or illness diagnosis). EIV-specific antibody response was measured by single radialhemolysis (SRH) and an EIV-nucleoprotein (NP) ELISA (used as a DIVA test). Overall immunitycoverage against EIV infection (i.e., titers induced by vaccination and/or natural infection above theclinical protection threshold) reached 87.6%. The EIV NP ELISA results showed that 83% of SRHpositive serum samples from young horses (≤3 years old) did not have NP antibodies, which indicatesthat the SRH antibody response was likely induced by EI vaccination alone (the HA recombinantcanarypoxvirus-based EI vaccine is mostly used in France) and supports the absence of EIV circulationin French horse populations between 2015 and late 2018, as reported by the French equine infectiousdiseases surveillance network (RESPE). Results from this study confirm a strong EI immunity in a largecohort of French horses, which provides an explanation to the lack of clinical EI in France in recentyears and highlights the success of vaccination against this disease. However, such EI protectionhas been challenged since late 2018 by the incursion in the EU of a Florida Clade 1 sub-lineage EIV(undetected in France since 2009), which is also reported here.

Mots clés: Equine influenza virus; Horse; Vaccination; Immune coverage; DIVA test; Surveillance; Epizooty; Florida Clade 1 (FC1)

Domaines: Médecine vétérinaire et santé animale

Stéphanie Fougerolle, Christine Fortier, Loïc Legrand, Marion Jourdan, Christel Marcillaud Pitel, et al.. Success and Limitation of Equine Influenza Vaccination: The First Incursion in a Decade of a Florida Clade 1 Equine Influenza Virus that Shakes Protection Despite High Vaccine Coverage. Vaccines, 2019, 7 (4), pp.174. ⟨10.3390/vaccines7040174⟩. ⟨hal-02372315⟩