EVANSVILLE, Ind., Feb. 25 (UPI) -- The latest of the three vaccine candidates developed by U.S. government scientists to prevent African swine fever in pigs seems to show the most promise, those scientist say, but it might be years before any becomes commercially available.
"This vaccine was 100 percent effective at a very low dose," said Douglas Gladue, a U.S. Department of Agriculture research microbiologist who developed the vaccine candidate with colleague Manuel Borca. "There was no sign of disease or fever in the animals."
Although these results -- announced in January -- are encouraging, Gladue said that getting a vaccine to work in a lab is just the first of many hurdles to mass producing one and distributing it to hog farmers across the country -- and the world.
First, the vaccine must go to a private company that has the manufacturing capability. The USDA is negotiating "licensing" agreements with unnamed private partners.
Once the companies have access to the vaccine, it must undergo more testing and work before it can be grown in larger quantities, said Liz Wagstrom, chief veterinarian at the National Pork Producers Council.
The three USDA vaccines were grown by using freshly harvested cells collected from live pigs. But, for a vaccine to be mass produced, it must be grown in a different kind of cell.
"Right now, every time you want to grow [a vaccine], you have to euthanize a pig and collect the cells," Wagstrom said. "That's not sustainable for mass production."
Vaccine companies maintain "banks" of what are called "immortal cells" in which they grow vaccines. These "immortal cell lines" grow in cultures and, as the name indicates, don't die, Wagstrom said.
The immortal cell lines differ from the live cells in which current vaccine candidates are grown, Wagstrom said. And vaccines created using live pig cells don't always survive the transfer to "immortal" cell lines.
If they do, they must be widely tested to ensure they are effective and don't harm the pigs.
After that, it could still take months -- if not years -- to grow enough vaccine to inoculate the nearly 75 million domestic hogs in the United States, much less the more than 500 million animals throughout the world.
"If vaccines can be developed from these candidates, it will take at least two to five years before it could reach the commercial market," said Tanya Brown, a USDA spokeswoman.
In the meantime, U.S. government scientists continue to try to create new -- more protective -- vaccine candidates, Gladue said. Private companies and universities around the world are doing their own research, as well.
In Spain, researchers have developed an oral vaccine that successfully immunized wild boars against African swine fever in early tests. In China, the Harbin Veterinary Research Institute is testing two potential vaccine candidates -- though many more unauthorized experimental vaccines are circulating among Chinese hog farmers.
With a viable vaccine likely still years away, the American swine industry is focusing its efforts on keeping the virus out by stepping up border protection efforts, as well as biosecurity measures on farms.
"I have a lot of confidence we are doing everything we can to keep it out," the pork producers' Wagstrom said.
The African swine fever virus continues to spread, decimating hog populations across the globe.
Before its appearance in China in August 2018, that nation raised more than half of the world's pigs. Estimates vary between 25 and 50 percent of those hogs have perished from the disease and culling.
Beyond China, the virus has spread to more than a dozen countries in Asia and eastern Europe. It recently spread into Indonesia and South Korea in Asia. In Europe, outbreaks in places like Poland threaten Germany's hogs. An outbreak in Belgium among wild pigs is moving closer to the French border.