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