For an equine influenza vaccination program to be effective, it must target the most recent forms of the virus. But influenza is constantly changing into new forms. Thus, keeping on top of these changes through monitoring and veterinary feedback is critical to keeping vaccines up-to-date, says an international group of researchers, and they’ve recently published a study describing their surveillance scheme.

The genetic material in equine influenza viruses reproduces through a special enzyme (RNA-dependent-RNA polymerase) with a high error rate, which leads to frequent changes in the virus genome. This means that each time the virus reproduces, there’s a good chance that it won’t reproduce in exactly the same way—be it a big change or a slight change. Those “antigenetic” changes might be a good thing for the virus and a bad thing for the horse. If the horse’s immune system doesn’t recognize the changed form of the virus, the horse can get sick from it, and the virus can spread.

As the numbers of changes accumulate, influenza viruses can diverge into new “sublineages.” And, if sufficient antigenic changes occur as a result of these mutations, the sublineages can be so different from the originating virus that existing vaccines are no longer effective in fighting against them, said Debra Elton, PhD, of the Animal Health Trust (AHT) in Newmarket, United Kingdom.

Unfortunately, researchers are unable to control this constant evolution of the influenza virus. “This process can’t be prevented,” she said.

What researchers can do, however, is keep up with the changes and m