The Effects of Biannual Equine Influenza Vaccine on Performance in Adult Horses

PICO question

In three day event horses, does biannual routine influenza vaccination compared to annual routine influenza vaccination reduce performance levels?

Clinical bottom line

There is no evidence that biannual equine influenza vaccination compared to annual booster vaccination in three day event horses is associated with reduced performance.

A group of five studies published over an 11 year period from one were evaluated. In adult warmblood horses there is weak evidence that exercise in the 28 day period post booster vaccination for equine influenza and equine herpes virus 1 and 4 (EHV1&4), is associated with changes in physical and clinical pathophysiological parameters including total red blood cell (RBC) count, neutrophil and lymphocyte count, fibrinogen concentration and serum proteins. These changes occurred at variable time points in the 14 days post exercise and values were not outside the published reference ranges for the reporting laboratories where published. Athletic performance of the horses was not evaluated.

No recommendations for equine influenza vaccination protocols in three day event horses can be made from the evidence.