Flu is a viral infection that is caused by influenza virus that involves the nose, throat and lungs. There are two types of influenza virus that can cause flu. They are influenza A and influenza B virus. Influenza A usually causes the infection between early winter and early spring, but the infection with influenza B can occur at any time of the year.
Expected duration of flu
Symptoms of flu start within 2 - 3 days (ranges from 1 to 7 days) of getting infected. The time period from getting infected to the appearance of symptoms is called incubation period. Incubation period of flu is very short and spreads easily from one person to another. So in a closed community like a school or workplace, most people develop symptoms within 2 or 3 weeks of the flu's arrival in the place.
Most cases of flu are mild, have an uncomplicated course and the prognosis is excellent. The symptoms start to improve in a week or two without long-term complications. Infection with flu does not provide life-long immunity i.e. after recovering from flu, you are at the risk of getting flu again in the next season.
During flu, infection symptoms such as fever, body pain, malaise and headache start to improve by day 2 and day 4 of the illness. After these symptoms begin to improve, you may develop symptoms, such as cough, sore throat, runny nose and sneezing. In most people these symptoms (except cough) usually improve in a few days and resolve in 4 - 7 days. Some people, however, may continue to have cough and malaise (feeling tired) for weeks.
Antiviral medications are not needed for everyone with flu. These medications are usually prescribed to people, who get very sick or are likely to develop complication of flu. The antiviral medicines when started within 2 days of the first symptoms work better and can shorten the time duration of illness by about 1 day.