Getting vaccinated every year is the best way to avoid getting sick with the flu. The flu, common cold and COVID-19 have similar symptoms. The flu and COVID-19 can be severe, but colds rarely are. What is the flu (influenza)? The flu is an illness you get from the influenza virus. Where is flu active today? Get Cold & Flu Activity Report for San Diego, CA (92101). Check Cold & Flu conditions in your area. Flu, also called influenza, is an infection of the nose, throat and lungs, which are part of the respiratory system. The flu is caused by a virus. Influenza viruses are different from the stomach flu viruses that cause diarrhea and vomiting. Most people with the flu get better on their own. This webpage provides data and reports about respiratory viruses that can cause cold and flu-like symptoms, including COVID-19, Influenza (Flu), and Respiratory Syncytial Virus (RSV). For other reportable diseases and conditions in San Diego County, visit Data and Reports. On this page: Where's the viz? During the fall and winter respiratory virus season, two types of flu can circulate: Influenza A viruses can mutate to cause novel viruses. Novel viruses are viruses that have not infected humans before. This means that humans have no immunity to novel viruses, so they cannot quickly fight them off. Flu is a contagious respiratory illness that infect the nose, throat, and sometimes the lungs. Learn about the current flu season and find resources related to flu surveillance and past seasons. Learn more about who is at higher risk of developing potentially serious flu complications. Flu activity in California (which includes San Diego) is currently moderate with 2.4% ILI. A current CDC Rt direction estimate is unavailable; use the weekly ILINet trend on the state flu page. Influenza (flu) is a contagious respiratory illness caused by influenza viruses. It spreads easily from person to person. It infects the nose, throat, and sometimes the lungs. It can cause mild to severe illness. In some cases, it can lead to death. On this page: Learn about identifying flu symptoms, how the diagnosis works, common complications, and more. Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four (typically two) days after exposure to the virus and last for about two to eight days.