1) Swine flu is a viral infection caused by H1N1 influenza viruses that normally infect pigs but can be transmitted to humans. 2) There was a large global outbreak of a new strain of H1N1 swine flu in 2009. 3) Symptoms of swine flu in humans include fever, cough, sore throat, runny nose, body aches, headaches, chills, fatigue and vomiting.