How long does the flu last? For most healthy people, the flu is an uncomfortable but short-term illness that resolves itself as the immune system fights it off. Symptoms usually appear from one to four days after exposure to the virus, and they last five to seven days. For people who've had a flu shot, the symptoms may last a shorter amount of time, or be less severe. For other people, the symptoms may last longer. Even when symptoms resolve, you may continue to feel fatigued. Some people are at increased risk for complications from influenza. 1  These people include: 2  the very young. 3  people 65 or older. 4  people with chronic illnesses, such as asthma, heart disease, HIV, or diabetes. 5  pregnant women. 6  people with a body mass index (BMI) of 40 or higher.