Equine influenza causes severe respiratory disease in susceptible horses and is preventable through vaccination, with outbreaks at equine events causing significant welfare consequences.
Equine influenza causes high fever, severe coughing, and profound malaise — the equine equivalent of severe human influenza — lasting up to two weeks in unvaccinated horses. Secondary bacterial pneumonia complicates some cases and can be fatal. Outbreaks at equine events spread infection rapidly through close proximity and shared water sources, affecting dozens to thousands of horses within days. The 2007 Australian outbreak demonstrated the catastrophic welfare scale of EIV outbreaks in unvaccinated populations. Regular vaccination that maintains immunity prevents individual horses from experiencing the significant suffering of clinical EIV disease, making vaccination one of the clearest welfare investments available to horse owners.