Recently published in Science, this research focused on creating transgenic chickens that did not transmit avian influenza virus to other chickens. The genetically modified chicken interferes with the viral replication machinery and stops the chickens from spreading the influenza virus. Although these "mutant" chickens were susceptible and did get sick from the infections, they did not transmit the virus.
The genetic modification comes in the form of introducing a new gene that produces a "decoy" molecule. Instead of the viral genome itself, the virus gets tricked into recognizing the decoy molecule. And thus, without proper recognition, the virus cannot replicate. The decoy plays a significant role in the flu virus genome and is present in all strains of influenza A. This is important because the mutant is not limited to one strain but has consequences for ALL strains of influenza A, which indicates that the researchers found and targeted a certain part of the genome that is conserved throughout the strains. This will free up many resources because the introduction of this new gene will no longer require constantly updated vaccines due to viral evolution and will efficiently help prevent spread of the virus.