The vaccine development project is led by Dr. Erwin van den Born, Senior Project Leader for Swine Biologicals R&D, and Dr. Ruud Segers, Head of R&D for Swine and Ruminant Biologicals at MSD Animal Health.
Dr. van den Born recalls a defining moment during trials with multiple vaccine candidates:
“We decided to include a strain with three deleted genes in one of our safety trials. While other candidates failed to meet safety standards, this one proved safe — the piglets remained healthy and protected. That’s when we knew we were on the right track.”
The so-called triple gene deletion mutant is a modified live ASF virus with deletions in three genes — Δ9GL, ΔUK, and ΔEP153R. This approach helps reduce virulence, improve viral stability, and preserve protective immunity.
According to Dr. Segers, ASF is an extremely complex virus with a large genome and high recombination potential, which makes creating a safe live vaccine a long-term challenge.
“We tested various vaccine types — subunit, vector, inactivated, DNA, and mRNA vaccines. None of them worked, except for live ones,” he explained.
To assess the stability of the vaccine strain, the MSD team conducted reversion-to-virulence trials in a Biosafety Level 3 (BSL-3) facility in the Netherlands. No signs of the virus reverting to a virulent form were found — a milestone that cleared the way for further development.
According to van den Born, the third gene deletion added an important benefit: it enables the creation of diagnostic tests that can differentiate the vaccine strain from the wild-type ASF virus.
The next phase involves field trials, currently underway at several farms in the Philippines, one of the countries hardest hit by ASF in Southeast Asia.
In cooperation with the Philippine government, MSD has already completed a tenfold overdose test, which showed no adverse clinical effects. The company is now conducting a large-scale trial involving 537 piglets and 76 pregnant sows across four farms.
Despite the promising progress, researchers refrain from giving even approximate timelines for commercialization.
“The process is complex and requires not only successful field trials but also production scale-up, GMP certification, and EU regulatory approval,” said Dr. Segers.
The MSD team has already achieved a key technical breakthrough — the ability to produce the vaccine in a clean, controlled cell line instead of relying on freshly isolated swine macrophages, simplifying production and improving consistency.
“We’ve assembled a multidisciplinary team — experts in biotechnology, molecular genetics, regulatory affairs, and intellectual property. The journey has been challenging, but we feel we’re getting close to the goal,” concluded Dr. van den Born.
The MSD Animal Health vaccine is considered one of the most promising ASF vaccine candidates worldwide. Successful completion of trials could mark a major milestone for the global swine industry, which continues to suffer from the devastating effects of African swine fever.
PigUA.info based on materials from Pig Progress