The vaccine candidate under development at the Agriculture Research Service (ARS), part of the US Department of Agriculture (USDA) passed an important safety test required for regulatory approval, moving the vaccine one step closer to commercial availability.
In an ARS news release the development was described as “an important milestone as part of a series of safety studies.” These new results show that USDA’s vaccine candidate does not revert to its normal virulence, after being injected into swine. That “reversion to virulence” test is required to ensure that the vaccine’s weakened form of the ASF virus does not revert to its original state.
These safety studies are necessary to gain approval for use in Vietnam and eventually in other countries around the world. Future commercial use, however, will depend on approval from the department of animal health within each requesting country.
Senior ARS scientist Dr Douglas Gladue is one of the developers of the virus. In the ARS news release, he said, “It is very hard to predict how selective pressure can cause a live attenuated vaccine to return to virulence. In the case of this particular vaccine candidate, ASFV-G-DI177L, we deleted a gene, which makes it difficult for the virus to simply add the gene back. So, we expected reversion to its original form to be unlikely, but the test still has to be performed.”
An attenuated vaccine strain retains much of its genetic makeup and could genetically change when exposed to various external circumstances. All live attenuated vaccines are weakened versions of a virus and can be used as a vaccine because the live vaccine virus will not cause illness and can still provide immunity.
Results of the tests were published in the peer-reviewed scientific title Viruses, which got published late April 2022. In the article, the researchers concluded, “Results from safety studies showed that ASFV-G-ΔI177L remains genetically stable and phenotypically attenuated during a five-passage reversion to virulence study in domestic swine. In addition, large-scale experiments to detect virus shedding and transmission confirmed that even under varying conditions, ASFV-G-ΔI177L is a safe live attenuated vaccine.”
The vaccine candidate was recently selected by the Vietnamese National Veterinary Joint Stock Company (Navetco) for commercial development in Vietnam. Navetco has partnered with ARS on ASF vaccine research and development since 2020. Further development will continue once the vaccine candidate receives regulatory approval from Vietnam.
The research article in Viruses was authored by Xuan Hanh Tran, Le Thi Thu Phuong, Nguyen Quang Huy, Do Thanh Thuy, Van Dung Nguyen, Pham Hào Quang, Quách Võ Ngôn, attached to Navetco, Ho Chi Minh City, Vietnam; Ayushi Rai, Cyril G. Gay, Dr Douglas Paul Gladue and Dr Manuel Victor Borca, ARS, USDA, United States.