An international team of scientists has found that a leading African swine fever (ASF) vaccine candidate can protect pigs against some virus strains but fails against others. This shows the need for region-tailored vaccines to control one of the world’s most devastating animal diseases.
The study, jointly conducted by the U.S. Department of Agriculture’s Plum Island Animal Disease Center and Nairobi-based International Livestock Research Institute (ILRI), evaluated a commercial live-attenuated vaccine known as ASFV-G-ΔI177L. Results revealed stark differences in its effectiveness depending on the viral strain.
Mixed Results Across Africa
When pigs were vaccinated and exposed to the same virus strain used to develop the vaccine, they remained healthy, while unvaccinated pigs quickly succumbed. The vaccine also provided partial protection, with about 80% of pigs surviving infection from a genetically distinct strain identified in Ghana.
However, it failed to protect against several other strains collected from Malawi, Kenya, South Africa, and Uganda—even though vaccinated pigs displayed strong immune responses.
“These findings reinforce the need to rethink our ASF vaccine strategies,” said Dr. Anna Lacasta, ILRI Senior Scientist. “A one-size-fits-all solution is unlikely. We need targeted vaccines aligned with the regional virus biotypes to maximize protection and control outbreaks.”
Rethinking Classification
The research also challenged current methods of classifying ASF viruses. Traditionally, strains have been grouped by a single gene, known as p72. But scientists discovered that two viruses with identical p72 sequences, Georgia2010 and Pret4, produced dramatically different outcomes in vaccinated pigs.
USDA scientists have since developed a new classification system that examines the entire set of protein-coding genes, offering a more accurate tool for predicting vaccine effectiveness.
“Although much further corroborative work is needed, the classification developed will likely be the only available rational approach for deciding vaccination procedures to control and manage ASFV outbreaks,” explained Dr. Manuel Borca, USDA scientist.
A Global Threat to Food Security
ASF is a highly contagious and often fatal disease affecting domestic and wild pigs. With no globally licensed vaccine currently available, the virus has ravaged pig populations across Africa, Asia, and Europe, inflicting massive economic losses and destabilizing food security.
Smallholder farmers in low and middle-income countries, especially women and youth reliant on backyard pig farming, are among the hardest hit. Beyond Africa, ASF poses an urgent threat to North America’s swine industries, which are valued at over USD 27 billion in the U.S. (2023) and CAD 6.3 billion in Canada (2024).
The research team recommends continued work to match vaccines to circulating virus types and to explore new vaccine designs with broader protection potential.
“Region-specific vaccines, informed by better genetic classification of the virus, represent the most promising pathway to safeguarding pig populations and protecting livelihoods,” Lacasta said.
