The title is a reference to a disease called Swine influenza, a broad group of viruses such as H5N1 responsible for influenza outbreaks that can affect pigs, birds, and humans, which is referenced in this episode.
The birds are all sick with the flu! It's a great chance for the pigs to grab the eggs if they can make it out without getting sick themselves!
Matilda was taking care of the Eggs when suddenly the Blues fell from a nearby tree. They looked very ill with red spots all over their bodies. She screamed as Red came by to check on her. Suddenly, Matilda and Red became infected.
Meanwhile, King Pig was seen outside looking through his telescope, until he saw the Eggs and the sneezing Red on guard. He became surprised and sent Corporal Pig and a few Minion Pigs to steal the Eggs. When the Pigs arrived near the eggs, one Minion Pig was out trying to snatch the eggs. Red spotted the Pig and tried to launch an attack, but sneezed and fainted in the process, causing him to lay on the ground. Corporal Pig finally grabbed the eggs and returned to Pig City. Back to Matilda and the Blues, she was making a antidote for the flu to recover herself and the Blues together. They came back to the eggs until they realized the Pigs stole them due to Red's sickness and defeat. Matilda began to get angry at the pigs because of the flu (a thunderstorm appeared in the background), and then the Birds went to Pig City.
Meanwhile, in Pig City, King Pig was waiting for Corporal Pig and his henchmen to arrive. Although they did returned, they appeared to have caught the flu. All the Pigs gasped naturally except King Pig who wanted to continue the celebration. He snatched the Eggs and got ready to eat them. As King Pig was about to eat scrambled eggs, all the Pigs got the flu of the same kind. Suddenly, the Birds, in hazmat suits, arrived. Red rushed out to save the Eggs and succeeded in doing so barely. As the Birds left the castle, Jim blew a raspberry at King Pig before leaving. In the end, King Pig also caught the flu.