Vaccine Licensing

Any company trying to put a new vaccine on the market must follow a specific process to obtain a license from the USDA before the product can be used in the horse population. A vaccine receives either a conditional or full license after a series of purity, safety, efficacy, and potency tests. But what does all of this licensing jargon mean? The Horse went to Larry Ludemann, DVM, a Senior Staff Veterinarian at USDA’s Center for Veterinary Biologics (CVB), where animal vaccines are reviewed and approved for use in the United States for help explaining the licensing subtleties to you.

New Viruses, New Vaccines

Vaccines are periodically developed because of new disease threats that arise in the United States, or because of new strains of diseases that are already in this country. The West Nile virus (WNV) vaccine is a good example of a vaccine developed in the face of a new disease threat.

The WNV vaccine, manufactured by Fort Dodge Animal Health, is a conditionally licensed product, meaning that in order to receive approval for distribution and use, the company had to show purity, quality, and a reasonable expectation of efficacy. (Fort Dodge did this and the vaccine was released with a conditional license on Aug. 1, 2001.) A vaccine with a conditional license is approved for use on a state-by-state basis, and the WNV vaccine is only available through a veterinarian.

Ludemann explained that for a reasonable expectation of efficacy for a WNV vaccine the company showed that horses would serologically respond to the vaccine. “There is some evidence in the literature that at a certain level, a serological titer is protective against WNV,” he said, “so based on that, if they could show that their product induces an immune response, we should have reasonable expectation that the vaccine is effective.

“A conditional license is issued on a one-year basis, and every year (the company has) to get it renewed,” explained Ludemann. “The company is generally required, as in this case, to show progress toward full licensing.” In the case of the WNV vaccine, that means making progress toward proving efficacy in a challenge study, and developing a potency test. “All vaccines have to be pure, safe, efficacious, and potent. For a potency test, every lot has to have the same level of antigen content as what was shown in the efficacy serial to be effective,” he said.

Fort Dodge completed efficacy trials on the WNV vaccine in May of this year, and the abstract of the results was presented Sept. 18 (see for a Q&A on the abstract). With completion of the study, the company showed significant progress toward attaining a full license, so the vaccine’s conditional license was renewed in July of 2002.

A challenge study of a vaccine must be a controlled study completed in a university setting or with the manufacturer. In the case of the WNV vaccine, researchers were dealing with a dangerous live virus (with which they challenged the horses), so it had to be completed in a Biosafety Level 3 containment facility.

When a vaccine is challenged in one of these studies, the USDA-CVB recommends the researchers replicate the most natural route of transmission. Horses generally contract the WNV through the bite of an infected mosquito. Researchers chose to challenge the horses by introducing the same amount of viremia to each with a needle, rather than employing mosquitoes. As long as they can demonstrate that the challenge was effective (by detecting viremia levels in the control horses that do not receive the vaccine), the route of challenge is acceptable.

“In general, we require 20 vaccinates and 10 control animals that are then challenged,” he explained. “You must show a significant difference between the vaccinates and the controls in prevention of disease. In the WNV vaccine’s case, prevention of viremia (was shown), with a significant difference between the vaccinates and the controls.”
The firm is allowed to pick whatever level (of antigen) they want to use to protect the animal--that’s what they call the minimum immunizing dose,” Ludemann explained. “Then every serial produced after that has to meet that minimal level.”

Finally, the company has to choose a time frame for which they want to assure that the vaccine is protective.

“We generally recommend one year (protection on the labels of other vaccines), but with these new antigens such as West Nile virus, they have to do a duration of immunity studies to support their (label) recommendations,” said Ludemann. In Fort Dodge’s case, scientists tested the duration of immunity to show that the vaccine product was still effective when a horse was challenged one year following vaccination.

The approval process to get a vaccine from unlicensed to fully licensed is an intricate set of requirements that takes, on average, about two to three years to complete.

According to Ludemann, the WNV vaccine received its conditional license quickly because there was such an obvious need for the vaccine with the rampant spread of WNV in horses, and because of its reasonable expectation of efficacy. Currently, Fort Dodge only has to tie up some loose ends with the potency tests before it receives a full license.

Once a vaccine receives a full license, restrictions on the distribution of the vaccine are lifted, and it will not have to be approved and distributed on a state-by-state basis. Ludemann said that under the conditional license, the WNV vaccine is restricted to use by veterinarians, but with a full licensure will probably come the ability for anyone to purchase and administer the vaccine.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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