Equine Influenza Vaccine Remains Effective Against Mutated Virus, Study Shows

Equine influenza virus mutates as it travels around the world from one animal to the next, and equine influenza vaccine must be updated periodically if the virus mutates to the point that the current vaccine does not adequately protect horses.

Romain Paillot, PhD, and his colleagues have been testing EI vaccines against a recent strain that caused outbreaks in Japan and Australia in 2007. They found that a non-updated EI vaccine (Duvaxyn IE T, which is available in Europe) does reduce clinical signs and virus shedding in previously unvaccinated ponies after two doses of vaccine. (The Duvaxyn vaccine was not used in either outbreak, but researchers wanted to know if it would protect against those EI strains.)

"The current equine influenza vaccines reduce the risk of infection, but an adequate update of vaccine strain is the best way to provide optimal vaccine protection against equine influenza," said Paillot, of the Animal Health Trust in Newmarket, UK.

Vaccines need to be modified when the differences between the influenza virus strain contained in the vaccine and the circulating influenza virus causing disease are too great (antigenic drift) and weaken protection induced by vaccination. The OIE (World Organization for Animal Health) expert surveillance panel on EI vaccine annually reviews worldwide information on EI virus circulation and antigenic variation and makes recommendations on vaccine strain composition and modification.

"It usually takes several years for vaccine manufacturers to update their equine influenza vaccines," he said, but it is still important to vaccinate against EI virus.

"In Japan, horses were vaccinated with an outdated equine influenza vaccine. The protection induced by vaccination was therefore sub-optimal but the outbreak was limited and only around 2,000 cases of equine influenza were reported. In Australia, where horses were unvaccinated, more than 75,000 to 100,000 horses were infected with equine influenza virus. The benefit of vaccination is very clear."

The study, "Efficacy of a whole inactivated EI vaccine against a recent EIV outbreak isolate and comparative detection of virus shedding" was published online ahead of print in March in Veterinary Immunology and Immunopathology.

The abstract is available on PubMed.

About the Author

Marie Rosenthal, MS

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