New West Nile Virus Vaccines for Horses Approved

New equine West Nile virus vaccines have been approved by the USDA. The vaccine line, called Vetera, is manufactured by Boehringer-Ingelheim, a privately held pharmaceutical company.

The Vetera line of West Nile virus vaccines "is the first new approach to a killed West Nile virus vaccine since 2001," stated Bob Stenbom, DVM, associate director of Equine Professional Services for Boehringer-Ingelheim.

There are three new vaccines in the Vetera West Nile virus line. The first is a monovalent that contains only a vaccine against West Nile virus. The second combines West Nile virus vaccine with Eastern equine encephalitis (EEE), Western equine encephalitis (WEE), and tetanus. The third vaccine combines all of the aforementioned plus Venezuelan equine encephalitis (VEE).

"We have color-coded the packaging and the vaccine bottles to help veterinarians quickly pick the correct vaccine from their supply," said Marion Tittle, senior brand manager for equine.

The technology used to make the new Vetera line of vaccines is unique in several ways. Stenbom noted that Vetera uses a different strain of the West Nile virus.

"We've seen a lot of changes in the genetic makeup (of the virus) since West Nile virus first entered this country in 1999," he noted. "The original strain of WNV (NY99) had a slow transmission. Then we saw a more rapid transmission as the virus made its way down the East Coast and through Florida and across the country. Genetic research since that time has shown it was a new strain (WN02) that did a much better job infecting mosquitoes and surviving in the environment. Vetera WNV vaccines incorporate an equine origin WNV strain (E159), representative of the more recent WNV strains impacting horses today."

He said all other West Nile virus vaccines on the U.S. market are based on the NY99 strain.

The second unique technology used in creating the Vetera line of vaccines is Ultrafil purification technique.

"You will hear a lot about this in the future," stated Stenbom. "Efficacy with few post-vaccination reactions is the goal of every vaccine. Extraneous proteins in vaccines from cell cultures and nutrients used in cell culture (used to grow the initial virus to make the vaccine) may cause problems with systemic vaccination reactions. Those reactions are not always caused by the desired vaccine components."

"Extraneous proteins should be filtered out as completely as possible from the finished vaccine to allow the immune system to remain 'undistracted' by irrelevant antigens," said Stenbom. "Ultrafil purification is a patent-pending process that allows optimal antigen loads in minimal dosage volumes and decreases the risk of post-vaccination reactions."

The third unique technology used in manufacturing Vetera is the Carbimmune adjuvant system that was developed about 10 years ago when Boehringer-Ingelheim used it in creating Calvenza equine influenza vaccines.

Adjuvants enhance the immune response to vaccine antigens. "Carbimmune adjuvant contains no sensitizing material of plant or animal origins," noted Stenbom. "It's a safe, flexible adjuvant system that is effective with a variety of antigens."

Stenbom explained that Carbimmune has the potential "to elicit higher levels of humoral antibody and cellular immunity than conventional aluminum hydroxide-based adjuvant systems."

He said Carbimmune acts like a sponge, so the antigens are dispersed on the surface and are drawn into the matrix of the molecule. The antigens on the surface of the Carbimmune matrix are available immediately when administered to give rapid onset of immunity. Then the "trapped" antigens deeper in the matrix offer a slow release of antigen that provide a longer duration of immunity.

The final piece of technology employed in the new Vetera vaccine line was how the vaccine was challenged with the intrathecal challenge model.

"Intrathecal challenge is considered to be the 'gold standard' for West Nile virus efficacy studies and the most aggressive challenge model," stated Stenbom.

The company noted that, according to information published by the American Association of Equine Practitioners in their "Guidelines for the Vaccination of Horses," the mosquito and needle challenge were the two models used in early West Nile virus studies. These methods resulted in only 10% of unvaccinated (control) horses showing signs of clinical disease when challenged. More recently, however, the intrathecal challenge model has been used, resulting in 90% to 100% of unvaccinated control horses developing grave signs of encephalomyelitis.

The name of the vaccines were derived because Boehringer-Ingelheim only sells vaccines to veterinarians (Vet-) and this new approach to creating equine vaccines launches a new era (-era) "in how equine vaccines should be made," Tittle said.

For more information ask your veterinarian or visit

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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