Published in npj Vaccines, the study raises concerns about the safety and efficacy of a vaccine that has already been used commercially. Researchers observed that after the vaccine was administered to pregnant sows, one of them exhibited moderate clinical signs of ASF.
Study Details
Researchers conducted three main experiments:
- Experiment 1 – Effects of ASFV-G-∆I177L Vaccination on Pregnant Sows and Their Offspring
Pregnant sows vaccinated with ASFV-G-∆I177L exhibited viremia and clinical signs of ASF, including fever and bluish discoloration of the teats. The offspring of vaccinated sows suffered significant losses: 43% of piglets were stillborn, and only 4 out of 23 live-born piglets survived. All piglets showed symptoms of ASF, and the virus was transmitted through the placenta.
- Experiment 2 – Reversion of ASFV-G-∆I177L to a Virulent Form Over Three Passages in Pigs
After multiple passages of the virus between animals, researchers observed a gradual loss of its attenuated phenotype. By the third passage, pigs exhibited severe ASF symptoms, including fever, lethargy, loss of appetite, neurological disorders, and high mortality rates.
- Experiment 3 – Safety Assessment of the Attenuated Virus After Four Passages
Even after significant dilution (up to 100,000 times), the ASFV-G-∆I177L strain that had undergone four passages remained virulent, causing severe clinical manifestations in pigs. This confirmed its ability to revert to a dangerous form.
Key Findings of the Study:
- ASFV-G-∆I177L is not genetically stable.
- The vaccine is not safe for use.
- The vaccine strain can revert to virulence when passaged in pigs.
- C257L mutations may contribute to increased virulence.
- ASF vaccine candidates must be tested for safety in pregnant animals.
This study highlights the importance of rigorous testing of ASF vaccines for safety and genetic stability. The findings raise concerns about the use of ASFV-G-∆I177L in commercial vaccines. Researchers recommend that ASF vaccine candidates undergo safety testing in pregnant animals to prevent potential adverse effects.
Background on ASF Vaccination Efforts
In June 2022, Vietnam announced the successful development of a vaccine to combat African swine fever, aiming to become the first country to commercially produce and export it. However, by August 2022, Vietnam temporarily suspended the use of its first domestically developed ASF vaccine, NAVET-ASFVAC, produced by Navetco (a company under the Ministry of Agriculture), after dozens of vaccinated pigs died.
The affected pigs were among approximately 600 pigs on several farms in Phu Yen province that received the NAVET-ASFVAC vaccine. The Ministry of Agriculture established a task force to investigate the pig deaths.
These events highlight the potential risks associated with live attenuated vaccines and the necessity for thorough safety testing and monitoring.
PigUA.info based on materials from www.nature.com