Duration of Immunity following oral and intramuscular Immunization with ASFV-G-ΔI177L

African swine fever is a devastating disease that has no cure and no widely approved vaccine, leaving pig farmers and wildlife managers with few options other than strict containment and culling of infected herds. The virus spreads easily among pigs and wild boar, causing a severe, often fatal illness that has disrupted global food supplies and threatened biodiversity. For years, scientists have been hunting for a safe way to stop the virus, with a particular focus on live attenuated vaccines. These are vaccines made from a weakened version of the virus itself; they train the animal's immune system to recognize the threat without causing the full-blown disease. One such candidate, a modified virus called ASFV-G-ΔI177L, has shown promise in earlier tests, but regulators need to know how long the protection lasts and whether the method of delivery matters. Specifically, they need to determine if giving the vaccine through a needle or through the mouth provides lasting safety, a question that is critical for protecting both domestic farms and free-roaming wild populations.

In a recent study conducted at the Friedrich-Loeffler-Institut in Germany, researchers set out to answer these questions by testing this specific vaccine on domestic pigs over a six-month period. They divided thirty young pigs into two groups: one group received the vaccine through a needle in the muscle, while the other group received it orally, mimicking how a wild boar might eat a bait containing the vaccine. The goal was to see if the vaccine would protect the animals for the entire typical lifespan of a fattening pig, which is roughly six months. After the initial vaccination, the scientists monitored the animals closely, checking their blood and swabs to see if the vaccine virus was present and if the pigs were developing antibodies, which are the proteins the immune system creates to fight infection. They found that the vaccine was well-tolerated by all the animals. The pigs given the shot developed antibodies quickly, while the oral group was a bit slower to respond, requiring a second dose to ensure most of them built up a defense. Over the following months, the vaccine virus remained detectable in some animals for up to four months, and antibody levels, though they dipped slightly over time, stayed present throughout the study.

Six months after the first vaccination, the true test began. The researchers introduced a highly virulent, or deadly, strain of the African swine fever virus to all the vaccinated pigs, as well as a small group of unvaccinated pigs to serve as a control. The results were stark. The unvaccinated control pigs and those in the oral group that had failed to respond to the vaccine developed high fevers and severe illness, forcing the researchers to humanely end their suffering within a week. However, the situation was very different for the pigs that had successfully responded to the vaccine. Every single pig that had responded to the oral vaccination survived the challenge, and most of the pigs that received the shot also survived. The survivors did show some mild symptoms, such as lethargy and coughing, but these were not caused by the African swine fever virus itself; further testing revealed they were suffering from a separate, unrelated respiratory infection. Crucially, the pigs that survived the deadly challenge were able to clear the virus from their bodies within twenty-eight days, whereas the unprotected animals carried massive amounts of the virus in their blood and tissues until the end.

The study also provided important insights into how the vaccine works depending on how it is given. While the oral route was less efficient at getting every animal to respond initially, those that did respond were protected just as well as, and in some cases better than, the animals that received the injection. The orally vaccinated survivors showed lower levels of virus in their blood and shed less virus through their noses and mouths compared to the injected group. This suggests that giving the vaccine by mouth might trigger a stronger defense at the point where the virus naturally enters the body, such as the nose and mouth, effectively blocking the infection before it can spread throughout the body. However, the study also highlighted that immunity is not a permanent shield for everyone. Two pigs that received the injection and had developed antibodies still fell ill and had to be euthanized, suggesting that for some individuals, the protective immunity may begin to fade around the six-month mark.

These findings offer a clear picture of the potential and the limitations of this vaccine candidate. The research demonstrates that ASFV-G-ΔI177L can provide substantial protection against a lethal viral challenge for at least six months, which covers the typical life of a market pig. The fact that oral vaccination can be just as effective as an injection for those who respond makes it a particularly attractive option for protecting wild boar populations, where delivering a needle is impossible. Yet, the study also confirms that the science is not yet perfect; the protection is not absolute for every single animal, and the duration of immunity may vary. As scientists continue to refine these vaccines, this work provides the essential data needed to move toward a licensed product that could finally help control this global threat to pig production and wildlife.