Equine influenza is a highly contagious respiratory disease causing significant suffering in unvaccinated horses — vaccination is inexpensive and effective but coverage remains incomplete.
Horses with influenza experience debilitating respiratory illness — the cough is severe, persistent, and painful, and the systemic illness causes fatigue and inappetence over weeks. Secondary pneumonia causes additional suffering and can be fatal. The welfare harm is entirely preventable in vaccinated horses. Outbreaks in unvaccinated populations spread rapidly through the horse community because social contact in competition, trail riding, and boarding creates constant exposure opportunities.