This article, The Flu, is a candidate for deletion.
It was never actually revealed in the show what the flu was, but on Talking Dead they revealed the flu was something that could infect you that day and you would be dead by night. In the actual show Rick says that we either gave the pigs the flu or the pigs gave it to us. After careful research I have made a conclusion on what the flu actually was. The Swine Flu! The swine flu was also known as The Spanish Flu. In the show whenever someone is bitten by a walker it takes minuets before the reanimate into a walker. Because of this we can think that the symptoms of the swine flu would be more deadly. The symptoms of the swine flu are as follows: watery, red eyes, vomiting, cough, fever, fatigue, etc. If we go along the route of the symptoms being more deadly, it would explain the bleeding eyes, vomiting of blood, cough, fever, and the fact that they are very tired. I feel that I have cracked the code on the flu in the walking dead during season 4.