African swine fever vaccine passes regulatory approval trials

Scientists at the USDA's Agricultural Research Service (ARS) announced that an African swine fever (ASF) vaccine candidate has passed an important safety test required for regulatory approval, bringing the vaccine one step closer to commercial availability.

The test is an important milestone in a series of safety studies. These new results show that the USDA vaccine candidate does not return to its normal virulence after administration to pigs. This “reversion to virulence” test is necessary to ensure that the weakened form of the ASF virus contained in the vaccine does not revert to its original state.

“This is an important milestone for the ASF vaccine candidate. These safety studies take this vaccine one step closer to being available on the market,” said ARS Senior Scientist Manuel Borca.

These safety studies are required to obtain approval for use in Vietnam and eventually elsewhere in the world. However, future commercial use will be subject to approval from the animal HEALTH department in each requesting country.

Although the virus is causing severe economic damage to the pig industry, there have been no outbreaks in the United States. The highly contagious ASF virus spread from Africa to Georgia in 2007 and has since swept through Central Europe and Asia before reaching the Dominican Republic in 2021.

"It's very difficult to predict how selective pressure could cause a live attenuated vaccine to return to virulence," said ARS Senior Scientist Douglas Gladew. “In the case of this particular vaccine candidate, ASFV-G-DI177L, we removed the gene, making it difficult for the virus to simply add the gene back. As such, we expected a return to its original form to be unlikely, but the test has yet to be performed."

An attenuated vaccine strain retains most of its genetic makeup and can be genetically altered by various external circumstances. All live attenuated vaccines are attenuated versions of the virus and can be used as a vaccine because the live vaccine virus does not cause disease and can still confer immunity.

The research is covered in an issue of the journal Viruses. A candidate vaccine was recently selected by NAVETCO for commercial development in Vietnam. NAVETCO has been collaborating with ARS on ASF vaccine research and development since 2020. Further development will continue once the vaccine candidate receives regulatory approval in Vietnam.