Equine influenza causes significant respiratory disease and can spread rapidly through horse populations. Vaccination is a fundamental welfare protection and biosecurity measure.
Equine influenza causes genuine respiratory distress — affected horses experience fever, severe cough, and debilitation that can persist for weeks. Seriously affected horses may develop pneumonia and in some cases die. The welfare case for vaccination is clear: the disease is preventable, the vaccine is safe and effective, and protection of the individual also protects the wider horse population through herd immunity. Outbreaks in unvaccinated populations spread rapidly through sharing of equipment, transport, and facilities. The welfare cost of a population-level outbreak — thousands of horses experiencing respiratory disease simultaneously — argues strongly for maintaining high vaccination coverage.